US20190284592A1

US20190284592A1 - Microorganisms and methods for the production of caprolactone

Info

Publication number: US20190284592A1
Application number: US16/433,804
Authority: US
Inventors: Anthony P. Burgard; Robin E. Osterhout; Priti Pharkya; Mark J. Burk
Original assignee: Genomatica Inc
Current assignee: Genomatica Inc
Priority date: 2011-11-02
Filing date: 2019-06-06
Publication date: 2019-09-19
Also published as: EP2773767A4; MY197970A; BR112014010448A2; WO2013067432A1; US9267162B2; US9719118B2; US20130144029A1; US8940509B2; MY171760A; US20210363556A1; US10351887B2; US20160355855A1; US20150353975A1; US20180135087A1; EP2773767A1; US11708592B2

Abstract

The invention provides non-naturally occurring microbial organisms containing caprolactone pathways having at least one exogenous nucleic acid encoding a butadiene pathway enzyme expressed in a sufficient amount to produce caprolactone. The invention additionally provides methods of using such microbial organisms to produce caprolactone by culturing a non-naturally occurring microbial organism containing caprolactone pathways as described herein under conditions and for a sufficient period of time to produce caprolactone.

Description

This application is a continuation of U.S. patent application Ser. No. 15/634,726, filed Jun. 27, 2017, which is a continuation of U.S. patent application Ser. No. 14/995,069 (now U.S. Pat. No. 9,719,118), filed Jan. 13, 2016, which is a continuation of U.S. patent application Ser. No. 14/596,072 (now U.S. Pat. No. 9,267,162), filed Jan. 13, 2015, which is a continuation of U.S. patent application Ser. No. 13/668,117 (now U.S. Pat. No. 8,940,509), filed Nov. 2, 2012 which claims the benefit of priority of U.S. Provisional application Ser. No. 61/554,920, filed Nov. 2, 2011, all of which are incorporated herein by reference in their entirety and for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates generally to biosynthetic processes, and more specifically to organisms having caprolactone capability.
Caprolactone (ε-Caprolactone) is a cyclic ester with a seven-membered ring having the formula (CH₂)₅CO₂. This colorless liquid is miscible with most organic solvents. It is produced as a precursor to caprolactam. The caprolactone monomer is used in the manufacture of highly specialized polymers because of its ring-opening potential. Ring-opening polymerization, for example, results in the production of polycaprolactone. Caprolactone is typically prepared by oxidation of cyclohexanone with peracetic acid.
Caprolactone undergoes reactions typical for primary alcohols. Downstream applications of these product groups include protective and industrial coatings, polyurethanes, cast elastomers, adhesives, colorants, pharmaceuticals and many more. Other useful properties of caprolactone include high resistance to hydrolysis, excellent mechanical properties, and low glass transition temperature.
Thus, there exists a need for methods for effectively producing compounds such as caprolactone. The present invention satisfies this need and provides related advantages as well.

SUMMARY OF INVENTION

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows exemplary pathways from adipate or adipyl-CoA to caprolactone. Enzymes are A. adipyl-CoA reductase, B. adipate semialdehyde reductase, C. 6-hydroxyhexanoyl-CoA transferase or synthetase, D. 6-hydroxyhexanoyl-CoA cyclase or spontaneous cyclization, E. adipate reductase, F. adipyl-CoA transferase, synthetase or hydrolase, G. 6-hydroxyhexanoate cyclase, H. 6-hydroxyhexanoate kinase, I. 6-hydroxyhexanoyl phosphate cyclase or spontaneous cyclization, J. phosphotrans-6-hydroxyhexanoylase.

FIG. 2 shows exemplary pathways from 4-hydroxybutyryl-CoA to caprolactone. Enzymes are A. 4-hydroxybutyryl-CoA:acetyl-CoA acyltransferase, B. 3-oxo-6-hydroxyhexanoyl-CoA reductase, C. 3,6-dihydroxyhexanoyl-CoA dehydratase, D. 6-hydroxyhex-2-enoyl-CoA reductase, E. 6-hydroxyhexanoyl-CoA transferase, synthetase or hydrolase, F. 6-hydroxyhexanoate cyclase, G. 6-hydroxyhexanoyl-CoA cyclase or spontaneous, H. phosphotrans-6-hydroxyhexanoylase, I. 6-hydroxyhexanoyl phosphate cyclase or spontaneous, J. 6-hydroxyhexanoate kinase.

FIG. 3 shows conversion of cyclohexanone to caprolactone by cyclohexanone monooxygenase.

FIG. 4 shows exemplary pathways to cyclohexanone from adipate semialdehyde. Enzymes are A. adipate semialdehyde dehydratase, B. cyclohexane-1,2-dione reductase, C. 2-hydroxycyclohexanone reductase, D. cyclohexane-1,2-diol dehydratase.

FIG. 5 shows exemplary pathways to cyclohexanone from pimeloyl-CoA. Enzymes are A. 2-ketocyclohexane-1-carboxoyl-CoA hydrolase (acting on C—C), B. 2-ketocyclohexane-1-carboxoyl-CoA transferase, synthetase or hydrolase, C. 2-ketocyclohexane-1-carboxylate decarboxylase.

FIG. 6 shows the reverse TCA cycle for fixation of CO₂on carbohydrates as substrates. The enzymatic transformations are carried out by the enzymes as shown.

FIG. 7 shows the pathway for the reverse TCA cycle coupled with carbon monoxide dehydrogenase and hydrogenase for the conversion of syngas to acetyl-CoA.

FIG. 8 shows Western blots of 10 micrograms ACS90 (lane 1), ACS91 (lane2), Mta98/99 (lanes 3 and 4) cell extracts with size standards (lane 5) and controls of M. thermoacetica CODH (Moth_1202/1203) or Mtr (Moth_1197) proteins (50, 150, 250, 350, 450, 500, 750, 900, and 1000 ng).

FIG. 9 shows CO oxidation assay results. Cells (M. thermoacetica or E. coli with the CODH/ACS operon; ACS90 or ACS91 or empty vector: pZA33S) were grown and extracts prepared. Assays were performed at 55° C. at various times on the day the extracts were prepared. Reduction of methylviologen was followed at 578 nm over a 120 sec time course.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to the design and production of cells and organisms having biosynthetic production capabilities for caprolactone. The invention, in particular, relates to the design of microbial organism capable of producing caprolactone by introducing one or more nucleic acids encoding a caprolactone pathway enzyme.
In one embodiment, the invention utilizes in silico stoichiometric models of Escherichia coli metabolism that identify metabolic designs for biosynthetic production of caprolactone. The results described herein indicate that metabolic pathways can be designed and recombinantly engineered to achieve the biosynthesis of caprolactone in Escherichia coli and other cells or organisms. Biosynthetic production of caprolactone, for example, for the in silico designs can be confirmed by construction of strains having the designed metabolic genotype. These metabolically engineered cells or organisms also can be subjected to adaptive evolution to further augment caprolactone biosynthesis, including under conditions approaching theoretical maximum growth.
In certain embodiments, the caprolactone biosynthesis characteristics of the designed strains make them genetically stable and particularly useful in continuous bioprocesses. Separate strain design strategies were identified with incorporation of different non-native or heterologous reaction capabilities into E. coli or other host organisms leading to caprolactone producing metabolic pathways from either adipyl-CoA, adipate, 4-hydroxybutyryl-CoA, adipate semialdehyde and pimeloyl-CoA. In silico metabolic designs were identified that resulted in the biosynthesis of caprolactone in microorganisms from each of these substrates or metabolic intermediates.
Strains identified via the computational component of the platform can be put into actual production by genetically engineering any of the predicted metabolic alterations, which lead to the biosynthetic production of caprolactone or other intermediate and/or downstream products. In yet a further embodiment, strains exhibiting biosynthetic production of these compounds can be further subjected to adaptive evolution to further augment product biosynthesis. The levels of product biosynthesis yield following adaptive evolution also can be predicted by the computational component of the system.
The maximum theoretical caprolactone yield from glucose is 0.80 mol/mol (0.51 g/g), according to the equation:
5C₆H₁₂O₆→4C₆H₁₀O₂+6CO₂+10H₂O
The pathways presented in FIGS. 1-5 achieve a yield of 0.80 moles caprolactone per mole of glucose utilized. Increasing product yields is possible if cells are capable of fixing CO₂through pathways such as the reductive TCA cycle or the Wood-Ljungdahl pathway and additional reducing equivalents are provided.
As used herein, the term “non-naturally occurring” when used in reference to a microbial organism or microorganism of the invention is intended to mean that the microbial organism has at least one genetic alteration not normally found in a naturally occurring strain of the referenced species, including wild-type strains of the referenced species. Genetic alterations include, for example, modifications introducing expressible nucleic acids encoding metabolic polypeptides, other nucleic acid additions, nucleic acid deletions and/or other functional disruption of the microbial organism's genetic material. Such modifications include, for example, coding regions and functional fragments thereof, for heterologous, homologous or both heterologous and homologous polypeptides for the referenced species. Additional modifications include, for example, non-coding regulatory regions in which the modifications alter expression of a gene or operon. Exemplary metabolic polypeptides include enzymes or proteins within a caprolactone biosynthetic pathway.
A metabolic modification refers to a biochemical reaction that is altered from its naturally occurring state. Therefore, non-naturally occurring microorganisms can have genetic modifications to nucleic acids encoding metabolic polypeptides, or functional fragments thereof. Exemplary metabolic modifications are disclosed herein.
As used herein, the term “isolated” when used in reference to a microbial organism is intended to mean an organism that is substantially free of at least one component as the referenced microbial organism is found in nature. The term includes a microbial organism that is removed from some or all components as it is found in its natural environment. The term also includes a microbial organism that is removed from some or all components as the microbial organism is found in non-naturally occurring environments. Therefore, an isolated microbial organism is partly or completely separated from other substances as it is found in nature or as it is grown, stored or subsisted in non-naturally occurring environments. Specific examples of isolated microbial organisms include partially pure microbes, substantially pure microbes and microbes cultured in a medium that is non-naturally occurring.
As used herein, the terms “microbial,” “microbial organism” or “microorganism” are intended to mean any organism that exists as a microscopic cell that is included within the domains of archaea, bacteria or eukarya. Therefore, the term is intended to encompass prokaryotic or eukaryotic cells or organisms having a microscopic size and includes bacteria, archaea and eubacteria of all species as well as eukaryotic microorganisms such as yeast and fungi. The term also includes cell cultures of any species that can be cultured for the production of a biochemical.
As used herein, the term “CoA” or “coenzyme A” is intended to mean an organic cofactor or prosthetic group (nonprotein portion of an enzyme) whose presence is required for the activity of many enzymes (the apoenzyme) to form an active enzyme system. Coenzyme A functions in certain condensing enzymes, acts in acetyl or other acyl group transfer and in fatty acid synthesis and oxidation, pyruvate oxidation and in other acetylation.
As used herein, the term “substantially anaerobic” when used in reference to a culture or growth condition is intended to mean that the amount of oxygen is less than about 10% of saturation for dissolved oxygen in liquid media. The term also is intended to include sealed chambers of liquid or solid medium maintained with an atmosphere of less than about 1% oxygen.
“Exogenous” as it is used herein is intended to mean that the referenced molecule or the referenced activity is introduced into the host microbial organism. The molecule can be introduced, for example, by introduction of an encoding nucleic acid into the host genetic material such as by integration into a host chromosome or as non-chromosomal genetic material such as a plasmid. Therefore, the term as it is used in reference to expression of an encoding nucleic acid refers to introduction of the encoding nucleic acid in an expressible form into the microbial organism. When used in reference to a biosynthetic activity, the term refers to an activity that is introduced into the host reference organism. The source can be, for example, a homologous or heterologous encoding nucleic acid that expresses the referenced activity following introduction into the host microbial organism. Therefore, the term “endogenous” refers to a referenced molecule or activity that is present in the host. Similarly, the term when used in reference to expression of an encoding nucleic acid refers to expression of an encoding nucleic acid contained within the microbial organism. The term “heterologous” refers to a molecule or activity derived from a source other than the referenced species whereas “homologous” refers to a molecule or activity derived from the host microbial organism. Accordingly, exogenous expression of an encoding nucleic acid of the invention can utilize either or both a heterologous or homologous encoding nucleic acid.
It is understood that when more than one exogenous nucleic acid is included in a microbial organism that the more than one exogenous nucleic acids refers to the referenced encoding nucleic acid or biosynthetic activity, as discussed above. It is further understood, as disclosed herein, that such more than one exogenous nucleic acids can be introduced into the host microbial organism on separate nucleic acid molecules, on polycistronic nucleic acid molecules, or a combination thereof, and still be considered as more than one exogenous nucleic acid. For example, as disclosed herein a microbial organism can be engineered to express two or more exogenous nucleic acids encoding a desired pathway enzyme or protein. In the case where two exogenous nucleic acids encoding a desired activity are introduced into a host microbial organism, it is understood that the two exogenous nucleic acids can be introduced as a single nucleic acid, for example, on a single plasmid, on separate plasmids, can be integrated into the host chromosome at a single site or multiple sites, and still be considered as two exogenous nucleic acids. Similarly, it is understood that more than two exogenous nucleic acids can be introduced into a host organism in any desired combination, for example, on a single plasmid, on separate plasmids, can be integrated into the host chromosome at a single site or multiple sites, and still be considered as two or more exogenous nucleic acids, for example three exogenous nucleic acids. Thus, the number of referenced exogenous nucleic acids or biosynthetic activities refers to the number of encoding nucleic acids or the number of biosynthetic activities, not the number of separate nucleic acids introduced into the host organism.
The non-naturally occurring microbial organisms of the invention can contain stable genetic alterations, which refers to microorganisms that can be cultured for greater than five generations without loss of the alteration. Generally, stable genetic alterations include modifications that persist greater than 10 generations, particularly stable modifications will persist more than about 25 generations, and more particularly, stable genetic modifications will be greater than 50 generations, including indefinitely.
Those skilled in the art will understand that the genetic alterations, including metabolic modifications exemplified herein, are described with reference to a suitable host organism such as E. coli and their corresponding metabolic reactions or a suitable source organism for desired genetic material such as genes for a desired metabolic pathway. However, given the complete genome sequencing of a wide variety of organisms and the high level of skill in the area of genomics, those skilled in the art will readily be able to apply the teachings and guidance provided herein to essentially all other organisms. For example, the E. coli metabolic alterations exemplified herein can readily be applied to other species by incorporating the same or analogous encoding nucleic acid from species other than the referenced species. Such genetic alterations include, for example, genetic alterations of species homologs, in general, and in particular, orthologs, paralogs or nonorthologous gene displacements.
An ortholog is a gene or genes that are related by vertical descent and are responsible for substantially the same or identical functions in different organisms. For example, mouse epoxide hydrolase and human epoxide hydrolase can be considered orthologs for the biological function of hydrolysis of epoxides. Genes are related by vertical descent when, for example, they share sequence similarity of sufficient amount to indicate they are homologous, or related by evolution from a common ancestor. Genes can also be considered orthologs if they share three-dimensional structure but not necessarily sequence similarity, of a sufficient amount to indicate that they have evolved from a common ancestor to the extent that the primary sequence similarity is not identifiable. Genes that are orthologous can encode proteins with sequence similarity of about 25% to 100% amino acid sequence identity. Genes encoding proteins sharing an amino acid similarity less that 25% can also be considered to have arisen by vertical descent if their three-dimensional structure also shows similarities. Members of the serine protease family of enzymes, including tissue plasminogen activator and elastase, are considered to have arisen by vertical descent from a common ancestor.
Orthologs include genes or their encoded gene products that through, for example, evolution, have diverged in structure or overall activity. For example, where one species encodes a gene product exhibiting two functions and where such functions have been separated into distinct genes in a second species, the three genes and their corresponding products are considered to be orthologs. For the production of a biochemical product, those skilled in the art will understand that the orthologous gene harboring the metabolic activity to be introduced or disrupted is to be chosen for construction of the non-naturally occurring microorganism. An example of orthologs exhibiting separable activities is where distinct activities have been separated into distinct gene products between two or more species or within a single species. A specific example is the separation of elastase proteolysis and plasminogen proteolysis, two types of serine protease activity, into distinct molecules as plasminogen activator and elastase. A second example is the separation of mycoplasma 5′-3′ exonuclease and Drosophila DNA polymerase III activity. The DNA polymerase from the first species can be considered an ortholog to either or both of the exonuclease or the polymerase from the second species and vice versa.
In contrast, paralogs are homologs related by, for example, duplication followed by evolutionary divergence and have similar or common, but not identical functions. Paralogs can originate or derive from, for example, the same species or from a different species. For example, microsomal epoxide hydrolase (epoxide hydrolase I) and soluble epoxide hydrolase (epoxide hydrolase II) can be considered paralogs because they represent two distinct enzymes, co-evolved from a common ancestor, that catalyze distinct reactions and have distinct functions in the same species. Paralogs are proteins from the same species with significant sequence similarity to each other suggesting that they are homologous, or related through co-evolution from a common ancestor. Groups of paralogous protein families include HipA homologs, luciferase genes, peptidases, and others.
A nonorthologous gene displacement is a nonorthologous gene from one species that can substitute for a referenced gene function in a different species. Substitution includes, for example, being able to perform substantially the same or a similar function in the species of origin compared to the referenced function in the different species. Although generally, a nonorthologous gene displacement will be identifiable as structurally related to a known gene encoding the referenced function, less structurally related but functionally similar genes and their corresponding gene products nevertheless will still fall within the meaning of the term as it is used herein. Functional similarity requires, for example, at least some structural similarity in the active site or binding region of a nonorthologous gene product compared to a gene encoding the function sought to be substituted. Therefore, a nonorthologous gene includes, for example, a paralog or an unrelated gene.
Therefore, in identifying and constructing the non-naturally occurring microbial organisms of the invention having caprolactone biosynthetic capability, those skilled in the art will understand with applying the teaching and guidance provided herein to a particular species that the identification of metabolic modifications can include identification and inclusion or inactivation of orthologs. To the extent that paralogs and/or nonorthologous gene displacements are present in the referenced microorganism that encode an enzyme catalyzing a similar or substantially similar metabolic reaction, those skilled in the art also can utilize these evolutionally related genes.
Orthologs, paralogs and nonorthologous gene displacements can be determined by methods well known to those skilled in the art. For example, inspection of nucleic acid or amino acid sequences for two polypeptides will reveal sequence identity and similarities between the compared sequences. Based on such similarities, one skilled in the art can determine if the similarity is sufficiently high to indicate the proteins are related through evolution from a common ancestor. Algorithms well known to those skilled in the art, such as Align, BLAST, Clustal W and others compare and determine a raw sequence similarity or identity, and also determine the presence or significance of gaps in the sequence which can be assigned a weight or score. Such algorithms also are known in the art and are similarly applicable for determining nucleotide sequence similarity or identity. Parameters for sufficient similarity to determine relatedness are computed based on well known methods for calculating statistical similarity, or the chance of finding a similar match in a random polypeptide, and the significance of the match determined. A computer comparison of two or more sequences can, if desired, also be optimized visually by those skilled in the art. Related gene products or proteins can be expected to have a high similarity, for example, 25% to 100% sequence identity. Proteins that are unrelated can have an identity which is essentially the same as would be expected to occur by chance, if a database of sufficient size is scanned (about 5%). Sequences between 5% and 24% may or may not represent sufficient homology to conclude that the compared sequences are related. Additional statistical analysis to determine the significance of such matches given the size of the data set can be carried out to determine the relevance of these sequences.
Exemplary parameters for determining relatedness of two or more sequences using the BLAST algorithm, for example, can be as set forth below. Briefly, amino acid sequence alignments can be performed using BLASTP version 2.0.8 (Jan. 5, 1999) and the following parameters: Matrix: 0 BLOSUM62; gap open: 11; gap extension: 1; x_dropoff: 50; expect: 10.0; wordsize: 3; filter: on. Nucleic acid sequence alignments can be performed using BLASTN version 2.0.6 (Sep. 16, 1998) and the following parameters: Match: 1; mismatch: −2; gap open: 5; gap extension: 2; x_dropoff: 50; expect: 10.0; wordsize: 11; filter: off. Those skilled in the art will know what modifications can be made to the above parameters to either increase or decrease the stringency of the comparison, for example, and determine the relatedness of two or more sequences.
In some embodiments, the invention provides a non-naturally occurring microbial organism having a caprolactone pathway and including at least one exogenous nucleic acid encoding a caprolactone pathway enzyme expressed in a sufficient amount to produce caprolactone. In some aspects of the invention, the caprolactone pathway includes a pathway selected from: (1) 1A, 1B, 1C and 1D; (2) 1E, 1B, 1C and 1D; (3) 1F, 1A, 1B, 1C and 1D; (4) 1F, 1E, 1B, 1C and 1D; (5) 1A, 1B and 1G; (6) 1E, 1B and 1G; (7) 1F, 1A, 1B and 1G; (8) 1F, 1E, 1B and 1G; (9) 1A, 1B, 1C, 1J and 1I; (10) 1E, 1B, 1C, 1J and 1I; (11) 1F, 1A, 1B, 1C, 1J and 1I; (12) 1F, 1E, 1B, 1C, 1J and 1I; (13) 1A, 1B, 1H and 1I; (14) 1E, 1B, 1H and 1I; (15) 1F, 1A, 1B, 1H and 1I; (16) 1F, 1E, 1B, 1H and 1I; (17) 2A, 2B, 2C, 2D, 2E and 2F; (18) 2A, 2B, 2C, 2D and 2G; (19) 2A, 2B, 2C, 2D, 2E, 2J and 2I; (20) 2A, 2B, 2C, 2D, 2H and 2I; (2I) 4A, 4B, 4C, 4D and 3A; and (22) 5A, 5B, 5C an 3A, wherein 1A is an adipyl-CoA reductase, wherein 1B is an adipate semialdehyde reductase, wherein 1C is a 6-hydroxyhexanoyl-CoA transferase or a 6-hydroxyhexanoyl-CoA synthetase, wherein 1D is a 6-hydroxyhexanoyl-CoA cyclase or spontaneous cyclization, wherein 1E is an adipate reductase, wherein 1F is an adipyl-CoA transferase, an adipyl-CoA synthetase or an adipyl-CoA hydrolase, wherein 1G is a 6-hydroxyhexanoate cyclase, wherein 1H is a 6-hydroxyhexanoate kinase, wherein 1I is a 6-hydroxyhexanoyl phosphate cyclase or spontaneous cyclization, wherein 1J is a phosphotrans-6-hydroxyhexanoylase, wherein 2A is a 4-hydroxybutyryl-CoA:acetyl-CoA acyltransferase, wherein 2B is a 3-oxo-6-hydroxyhexanoyl-CoA reductase, wherein 2C is a 3,6-dihydroxyhexanoyl-CoA dehydratase, wherein 2D is a 6-hydroxyhex-2-enoyl-CoA reductase, wherein 2E is a 6-hydroxyhexanoyl-CoA transferase, a 6-hydroxyhexanoyl-CoA synthetase or a 6-hydroxyhexanoyl-CoA hydrolase, wherein 2F is a 6-hydroxyhexanoate cyclase, wherein 2G is a 6-hydroxyhexanoyl-CoA cyclase or spontaneous cyclization, wherein 2H is a phosphotrans-6-hydroxyhexanoylase, wherein 2I is a 6-hydroxyhexanoyl phosphate cyclase or spontaneous cyclization, wherein 2J is a 6-hydroxyhexanoate kinase, wherein 3A is a cyclohexanone monooxygenase, wherein 4A is an adipate semialdehyde dehydratase, wherein 4B is a cyclohexane-1,2-dione reductase, wherein 4C is a 2-hydroxycyclohexanone reductase, wherein 4D is a cyclohexane-1,2-diol dehydratase, wherein 5A is a 2-ketocyclohexane-1-carboxoyl-CoA hydrolase (acting on C—C), wherein 5B is a 2-ketocyclohexane-1-carboxoyl-CoA transferase, a 2-ketocyclohexane-1-carboxoyl-CoA synthetase or a 2-ketocyclohexane-1-carboxoyl-CoA hydrolase, and wherein 5C is a 2-ketocyclohexane-1-carboxylate decarboxylase.
In one embodiment, the invention provides a non-naturally occurring microbial organism as described herein, wherein the microbial organism includes two, three, four, five, six or seven exogenous nucleic acids each encoding a caprolactone pathway enzyme. For example, the microbial organism can include exogenous nucleic acids encoding each of the enzymes of at least one of the pathways selected from (1)-(22) as described above.
In one embedment, at least one exogenous nucleic acid included within the microbial organism is a heterologous nucleic acid. In another aspect, the non-naturally occurring microbial organism as disclosed herein is in a substantially anaerobic culture medium.
In one embodiment, the non-naturally occurring microbial organism as disclosed herein further includes (i) a reductive TCA pathway comprising at least one exogenous nucleic acid encoding a reductive TCA pathway enzyme, wherein said at least one exogenous nucleic acid is selected from an ATP-citrate lyase, citrate lyase, a fumarate reductase, and an alpha-ketoglutarate:ferredoxin oxidoreductase; (ii) a reductive TCA pathway comprising at least one exogenous nucleic acid encoding a reductive TCA pathway enzyme, wherein said at least one exogenous nucleic acid is selected from a pyruvate:ferredoxin oxidoreductase, a phosphoenolpyruvate carboxylase, a phosphoenolpyruvate carboxykinase, a CO dehydrogenase, and an H₂hydrogenase; or (iii) at least one exogenous nucleic acid encodes an enzyme selected from a CO dehydrogenase, an H₂hydrogenase, and combinations thereof.
In another aspect of the invention, non-naturally occurring microbial organism having (i) above, further includes an exogenous nucleic acid encoding an enzyme selected from a pyruvate:ferredoxin oxidoreductase, an aconitase, an isocitrate dehydrogenase, a succinyl-CoA synthetase, a succinyl-CoA transferase, a fumarase, a malate dehydrogenase, an acetate kinase, a phosphotransacetylase, an acetyl-CoA synthetase, an NAD(P)H:ferredoxin oxidoreductase, ferredoxin, and combinations thereof. In another aspect, the non-naturally occurring microbial organism including (ii) as described above further includes an exogenous nucleic acid encoding an enzyme selected from an aconitase, an isocitrate dehydrogenase, a succinyl-CoA synthetase, a succinyl-CoA transferase, a fumarase, a malate dehydrogenase, and combinations thereof.
In one aspect of the invention, the non-naturally occurring microbial organism having (i) as described above further comprises four exogenous nucleic acids encoding an ATP-citrate lyase, citrate lyase, a fumarate reductase, and an alpha-ketoglutarate:ferredoxin oxidoreductase. In one aspect of the invention, the non-naturally occurring microbial organism having (ii) as described above further comprises five exogenous nucleic acids encoding a pyruvate:ferredoxin oxidoreductase, a phosphoenolpyruvate carboxylase, a phosphoenolpyruvate carboxykinase, a CO dehydrogenase, and an H₂hydrogenase. In one aspect of the invention, the non-naturally occurring microbial organism having (iii) as described above further comprises two exogenous nucleic acids encoding a CO dehydrogenase and an H₂hydrogenase.
In an additional embodiment, the invention provides a non-naturally occurring microbial organism having a caprolactone pathway, wherein the non-naturally occurring microbial organism comprises at least one exogenous nucleic acid encoding an enzyme or protein that converts a substrate to a product selected from the group consisting of adipyl-CoA to adipate, adipyl-CoA to adipate semialdehyde, adipate to adipate semialdehyde, adipate semialdehyde to 6-hydroxyhexanoate, 6-hydroxyhexanoate to 6-hydroxyhexanoyl-CoA, 6-hydroxyhexanoate to 6-hydroxyhexanoyl-phosphate, 6-hydroxyhexanoate to caprolactone, 6-hydroxyhexanoyl-CoA to 6-hydroxyhexanoyl phosphate, 6-hydroxyhexanoyl phosphate to caprolactone, 6-hydroxyhexanoyl-CoA to caprolactone, 4-hydroxybutyryl-CoA to 3-oxo-6-hydroxy hexanoyl-CoA, to 3-oxo-6-hydroxy hexanoyl-CoA to 3,6-dihydroxy hexanoyl-CoA, 3,6-dihydroxy hexanoyl-CoA to 6-hydroxyhex-2-enoyl-CoA, 6-hydroxyhex-2-enoyl-CoA to 6-hydroxyhexanoyl-CoA, 6-hydroxyhexanoyl-CoA to 6-hydroxyhexanoate, cyclohexanon to caprolactone, adipate semialdehyde to cyclohexane-1,2-dione, cyclohexane-1,2-dione to 2-hydroxycyclohexanone, to 2-hydroxycyclohexanone to cyclohexane-1,2-diol, cyclohexane-1,2-diol to cyclohexone, pimeloyl-CoA to 2-ketocyclohexone-1-carboxoyl-CoA, 2-ketocyclohexone-1-carboxoyl-CoA to 2-ketocyclohexane-1-carboxylate, and 2-ketocyclohexane-1-carboxylate to cyclohexanone. One skilled in the art will understand that these are merely exemplary and that any of the substrate-product pairs disclosed herein suitable to produce a desired product and for which an appropriate activity is available for the conversion of the substrate to the product can be readily determined by one skilled in the art based on the teachings herein. Thus, the invention provides a non-naturally occurring microbial organism containing at least one exogenous nucleic acid encoding an enzyme or protein, where the enzyme or protein converts the substrates and products of a caprolactone pathway, such as that shown in FIGS. 1-5.
While generally described herein as a microbial organism that contains a caprolactone pathway, it is understood that the invention additionally provides a non-naturally occurring microbial organism comprising at least one exogenous nucleic acid encoding a caprolactone pathway enzyme expressed in a sufficient amount to produce an intermediate of a caprolactone pathway. For example, as disclosed herein, a caprolactone pathway is exemplified in FIGS. 1-5. Therefore, in addition to a microbial organism containing a caprolactone pathway that produces caprolactone, the invention additionally provides a non-naturally occurring microbial organism comprising at least one exogenous nucleic acid encoding a caprolactone pathway enzyme, where the microbial organism produces a caprolactone pathway intermediate, for example, 6-hydroxyhexanoate, 6-hydroxyhexanoyl-CoA, 6-hydroxyhexanoyl phosphate, 3-oxo-6-hydroxy hexanoyl-CoA, 3,6-dihydroxy hexanoyl-CoA, 6-hydroxyhex-2-enoyl-CoA, cyclohexanone, cyclohexane-1,2-dione, 2-hydroxycyclohexanone, cyclohexane-1,2-diol, 2-ketocyclohexane-1-carboxyoyl-CoA, or 2-ketocyclohexane-1-carboxylate.
It is understood that any of the pathways disclosed herein, as described in the Examples and exemplified in the Figures, including the pathways of FIGS. 1-5, can be utilized to generate a non-naturally occurring microbial organism that produces any pathway intermediate or product, as desired. As disclosed herein, such a microbial organism that produces an intermediate can be used in combination with another microbial organism expressing downstream pathway enzymes to produce a desired product. However, it is understood that a non-naturally occurring microbial organism that produces a caprolactone pathway intermediate can be utilized to produce the intermediate as a desired product.
This invention is also directed, in part to engineered biosynthetic pathways to improve carbon flux through a central metabolism intermediate en route to caprolactone. The present invention provides non-naturally occurring microbial organisms having one or more exogenous genes encoding enzymes that can catalyze various enzymatic transformations en route to caprolactone. In some embodiments, these enzymatic transformations are part of the reductive tricarboxylic acid (RTCA) cycle and are used to improve product yields, including but not limited to, from carbohydrate-based carbon feedstock.
In numerous engineered pathways, realization of maximum product yields based on carbohydrate feedstock is hampered by insufficient reducing equivalents or by loss of reducing equivalents and/or carbon to byproducts. In accordance with some embodiments, the present invention increases the yields of caprolactone by (i) enhancing carbon fixation via the reductive TCA cycle, and/or (ii) accessing additional reducing equivalents from gaseous carbon sources and/or syngas components such as CO, CO₂, and/or H₂. In addition to syngas, other sources of such gases include, but are not limited to, the atmosphere, either as found in nature or generated.
The CO₂-fixing reductive tricarboxylic acid (RTCA) cycle is an endergenic anabolic pathway of CO₂assimilation which uses reducing equivalents and ATP (FIG. 6). One turn of the RTCA cycle assimilates two moles of CO₂into one mole of acetyl-CoA, or four moles of CO₂into one mole of oxaloacetate. This additional availability of acetyl-CoA improves the maximum theoretical yield of product molecules derived from carbohydrate-based carbon feedstock. Exemplary carbohydrates include but are not limited to glucose, sucrose, xylose, arabinose and glycerol.
In some embodiments, the reductive TCA cycle, coupled with carbon monoxide dehydrogenase and/or hydrogenase enzymes, can be employed to allow syngas, CO₂, CO, H₂, and/or other gaseous carbon source utilization by microorganisms. Synthesis gas (syngas), in particular is a mixture of primarily H₂and CO, sometimes including some amounts of CO₂, that can be obtained via gasification of any organic feedstock, such as coal, coal oil, natural gas, biomass, or waste organic matter. Numerous gasification processes have been developed, and most designs are based on partial oxidation, where limiting oxygen avoids full combustion, of organic materials at high temperatures (500-1500° C.) to provide syngas as a 0.5:1-3:1 H₂/CO mixture. In addition to coal, biomass of many types has been used for syngas production and represents an inexpensive and flexible feedstock for the biological production of renewable chemicals and fuels. Carbon dioxide can be provided from the atmosphere or in condensed from, for example, from a tank cylinder, or via sublimation of solid CO₂. Similarly, CO and hydrogen gas can be provided in reagent form and/or mixed in any desired ratio. Other gaseous carbon forms can include, for example, methanol or similar volatile organic solvents.
The components of synthesis gas and/or other carbon sources can provide sufficient CO₂, reducing equivalents, and ATP for the reductive TCA cycle to operate. One turn of the RTCA cycle assimilates two moles of CO₂into one mole of acetyl-CoA and requires 2 ATP and 4 reducing equivalents. CO and/or H₂can provide reducing equivalents by means of carbon monoxide dehydrogenase and hydrogenase enzymes, respectively. Reducing equivalents can come in the form of NADH, NADPH, FADH, reduced quinones, reduced ferredoxins, reduced flavodoxins and thioredoxins. The reducing equivalents, particularly NADH, NADPH, and reduced ferredoxin, can serve as cofactors for the RTCA cycle enzymes, for example, malate dehydrogenase, fumarate reductase, alpha-ketoglutarate:ferredoxin oxidoreductase (alternatively known as 2-oxoglutarate:ferredoxin oxidoreductase, alpha-ketoglutarate synthase, or 2-oxoglutarate synthase), pyruvate:ferredoxin oxidoreductase and isocitrate dehydrogenase. The electrons from these reducing equivalents can alternatively pass through an ion-gradient producing electron transport chain where they are passed to an acceptor such as oxygen, nitrate, oxidized metal ions, protons, or an electrode. The ion-gradient can then be used for ATP generation via an ATP synthase or similar enzyme.
The reductive TCA cycle was first reported in the green sulfur photosynthetic bacterium Chlorobium limicola (Evans et al., Proc. Natl. Acad. Sci. U.S.A. 55:928-934 (1966)). Similar pathways have been characterized in some prokaryotes (proteobacteria, green sulfur bacteria and thermophillic Knallgas bacteria) and sulfur-dependent archaea (Hugler et al., J. Bacteriol. 187:3020-3027 (2005; Hugler et al., Environ. Microbiol. 9:81-92 (2007). In some cases, reductive and oxidative (Krebs) TCA cycles are present in the same organism (Hugler et al., supra (2007); Siebers et al., J. Bacteriol. 186:2179-2194 (2004)). Some methanogens and obligate anaerobes possess incomplete oxidative or reductive TCA cycles that may function to synthesize biosynthetic intermediates (Ekiel et al., J. Bacteriol. 162:905-908 (1985); Wood et al., FEMS Microbiol. Rev. 28:335-352 (2004)).
The key carbon-fixing enzymes of the reductive TCA cycle are alpha-ketoglutarate:ferredoxin oxidoreductase, pyruvate:ferredoxin oxidoreductase and isocitrate dehydrogenase. Additional carbon may be fixed during the conversion of phosphoenolpyruvate to oxaloacetate by phosphoenolpyruvate carboxylase or phosphoenolpyruvate carboxykinase or by conversion of pyruvate to malate by malic enzyme.
Many of the enzymes in the TCA cycle are reversible and can catalyze reactions in the reductive and oxidative directions. However, some TCA cycle reactions are irreversible in vivo and thus different enzymes are used to catalyze these reactions in the directions required for the reverse TCA cycle. These reactions are: (1) conversion of citrate to oxaloacetate and acetyl-CoA, (2) conversion of fumarate to succinate, and (3) conversion of succinyl-CoA to alpha-ketoglutarate. In the TCA cycle, citrate is formed from the condensation of oxaloacetate and acetyl-CoA. The reverse reaction, cleavage of citrate to oxaloacetate and acetyl-CoA, is ATP-dependent and catalyzed by ATP-citrate lyase, or citryl-CoA synthetase and citryl-CoA lyase. Alternatively, citrate lyase can be coupled to acetyl-CoA synthetase, an acetyl-CoA transferase, or phosphotransacetylase and acetate kinase to form acetyl-CoA and oxaloacetate from citrate. The conversion of succinate to fumarate is catalyzed by succinate dehydrogenase while the reverse reaction is catalyzed by fumarate reductase. In the TCA cycle succinyl-CoA is formed from the NAD(P)⁺ dependent decarboxylation of alpha-ketoglutarate by the alpha-ketoglutarate dehydrogenase complex. The reverse reaction is catalyzed by alpha-ketoglutarate:ferredoxin oxidoreductase.
An organism capable of utilizing the reverse tricarboxylic acid cycle to enable production of acetyl-CoA-derived products on 1) CO, 2) CO₂and H₂, 3) CO and CO₂, 4) synthesis gas comprising CO and H₂, and 5) synthesis gas or other gaseous carbon sources comprising CO, CO₂, and H₂can include any of the following enzyme activities: ATP-citrate lyase, citrate lyase, aconitase, isocitrate dehydrogenase, alpha-ketoglutarate:ferredoxin oxidoreductase, succinyl-CoA synthetase, succinyl-CoA transferase, fumarate reductase, fumarase, malate dehydrogenase, acetate kinase, phosphotransacetylase, acetyl-CoA synthetase, acetyl-CoA transferase, pyruvate:ferredoxin oxidoreductase, NAD(P)H:ferredoxin oxidoreductase, carbon monoxide dehydrogenase, hydrogenase, and ferredoxin (see FIG. 7). Enzymes and the corresponding genes required for these activities are described herein.
Carbon from syngas or other gaseous carbon sources can be fixed via the reverse TCA cycle and components thereof. Specifically, the combination of certain carbon gas-utilization pathway components with the pathways for formation of caprolactone from acetyl-CoA results in high yields of these products by providing an efficient mechanism for fixing the carbon present in carbon dioxide, fed exogenously or produced endogenously from CO, into acetyl-CoA.
In some embodiments, a caprolactone pathway in a non-naturally occurring microbial organism of the invention can utilize any combination of (1) CO, (2) CO₂, (3) H₂, or mixtures thereof to enhance the yields of biosynthetic steps involving reduction, including addition to driving the reductive TCA cycle.
In some embodiments a non-naturally occurring microbial organism having an caprolactone pathway includes at least one exogenous nucleic acid encoding a reductive TCA pathway enzyme. The at least one exogenous nucleic acid is selected from an ATP-citrate lyase, citrate lyase, a fumarate reductase, isocitrate dehydrogenase, aconitase, and an alpha-ketoglutarate:ferredoxin oxidoreductase; and at least one exogenous enzyme selected from a carbon monoxide dehydrogenase, a hydrogenase, a NAD(P)H:ferredoxin oxidoreductase, and a ferredoxin, expressed in a sufficient amount to allow the utilization of (1) CO, (2) CO₂, (3) H₂, (4) CO₂and H₂, (5) CO and CO₂, (6) CO and H₂, or (7) CO, CO₂, and H₂.
In some embodiments a method includes culturing a non-naturally occurring microbial organism having a caprolactone pathway also comprising at least one exogenous nucleic acid encoding a reductive TCA pathway enzyme. The at least one exogenous nucleic acid is selected from an ATP-citrate lyase, citrate lyase, a fumarate reductase, isocitrate dehydrogenase, aconitase, and an alpha-ketoglutarate:ferredoxin oxidoreductase. Additionally, such an organism can also include at least one exogenous enzyme selected from a carbon monoxide dehydrogenase, a hydrogenase, a NAD(P)H:ferredoxin oxidoreductase, and a ferredoxin, expressed in a sufficient amount to allow the utilization of (1) CO, (2) CO₂, (3) H₂, (4) CO₂and H₂, (5) CO and CO₂, (6) CO and H₂, or (7) CO, CO₂, and H₂to produce a product.
In some embodiments a non-naturally occurring microbial organism having an caprolactone pathway further includes at least one exogenous nucleic acid encoding a reductive TCA pathway enzyme expressed in a sufficient amount to enhance carbon flux through acetyl-CoA. The at least one exogenous nucleic acid is selected from an ATP-citrate lyase, citrate lyase, a fumarate reductase, a pyruvate:ferredoxin oxidoreductase, isocitrate dehydrogenase, aconitase and an alpha-ketoglutarate:ferredoxin oxidoreductase.
In some embodiments a non-naturally occurring microbial organism having an caprolactone pathway includes at least one exogenous nucleic acid encoding an enzyme expressed in a sufficient amount to enhance the availability of reducing equivalents in the presence of carbon monoxide and/or hydrogen, thereby increasing the yield of redox-limited products via carbohydrate-based carbon feedstock. The at least one exogenous nucleic acid is selected from a carbon monoxide dehydrogenase, a hydrogenase, an NAD(P)H:ferredoxin oxidoreductase, and a ferredoxin. In some embodiments, the present invention provides a method for enhancing the availability of reducing equivalents in the presence of carbon monoxide or hydrogen thereby increasing the yield of redox-limited products via carbohydrate-based carbon feedstock, such as sugars or gaseous carbon sources, the method includes culturing this non-naturally occurring microbial organism under conditions and for a sufficient period of time to produce caprolactone.
In some embodiments, the non-naturally occurring microbial organism having an caprolactone pathway includes two exogenous nucleic acids, each encoding a reductive TCA pathway enzyme. In some embodiments, the non-naturally occurring microbial organism having an caprolactone pathway includes three exogenous nucleic acids each encoding a reductive TCA pathway enzyme. In some embodiments, the non-naturally occurring microbial organism includes three exogenous nucleic acids encoding an ATP-citrate lyase, a fumarate reductase, and an alpha-ketoglutarate:ferredoxin oxidoreductase. In some embodiments, the non-naturally occurring microbial organism includes three exogenous nucleic acids encoding a citrate lyase, a fumarate reductase, and an alpha-ketoglutarate:ferredoxin oxidoreductase. In some embodiments, the non-naturally occurring microbial organism includes four exogenous nucleic acids encoding a pyruvate:ferredoxin oxidoreductase; a phosphoenolpyruvate carboxylase or a phosphoenolpyruvate carboxykinase, a CO dehydrogenase; and an H₂hydrogenase. In some embodiments, the non-naturally occurring microbial organism includes two exogenous nucleic acids encoding a CO dehydrogenase and an H₂hydrogenase.
In some embodiments, the non-naturally occurring microbial organisms having an caprolactone pathway further include an exogenous nucleic acid encoding an enzyme selected from a pyruvate:ferredoxin oxidoreductase, an aconitase, an isocitrate dehydrogenase, a succinyl-CoA synthetase, a succinyl-CoA transferase, a fumarase, a malate dehydrogenase, an acetate kinase, a phosphotransacetylase, an acetyl-CoA synthetase, an NAD(P)H:ferredoxin oxidoreductase, and combinations thereof.
In some embodiments, the non-naturally occurring microbial organism having an caprolactone pathway further includes an exogenous nucleic acid encoding an enzyme selected from carbon monoxide dehydrogenase, acetyl-CoA synthase, ferredoxin, NAD(P)H:ferredoxin oxidoreductase and combinations thereof.
In some embodiments, the non-naturally occurring microbial organism having an caprolactone pathway utilizes a carbon feedstock selected from (1) CO, (2) CO₂, (3) CO₂and H₂, (4) CO and H₂, or (5) CO, CO₂, and H₂. In some embodiments, the non-naturally occurring microbial organism having an caprolactone pathway utilizes hydrogen for reducing equivalents. In some embodiments, the non-naturally occurring microbial organism having an caprolactone pathway utilizes CO for reducing equivalents. In some embodiments, the non-naturally occurring microbial organism having an caprolactone pathway utilizes combinations of CO and hydrogen for reducing equivalents.
In some embodiments, the non-naturally occurring microbial organism having an caprolactone pathway further includes one or more nucleic acids encoding an enzyme selected from a phosphoenolpyruvate carboxylase, a phosphoenolpyruvate carboxykinase, a pyruvate carboxylase, and a malic enzyme.
In some embodiments, the non-naturally occurring microbial organism having an caprolactone pathway further includes one or more nucleic acids encoding an enzyme selected from a malate dehydrogenase, a fumarase, a fumarate reductase, a succinyl-CoA synthetase, and a succinyl-CoA transferase.
In some embodiments, the non-naturally occurring microbial organism having an caprolactone pathway further includes at least one exogenous nucleic acid encoding a citrate lyase, an ATP-citrate lyase, a citryl-CoA synthetase, a citryl-CoA lyase an aconitase, an isocitrate dehydrogenase, a succinyl-CoA synthetase, a succinyl-CoA transferase, a fumarase, a malate dehydrogenase, an acetate kinase, a phosphotransacetylase, an acetyl-CoA synthetase, and a ferredoxin.
The invention is described herein with general reference to the metabolic reaction, reactant or product thereof, or with specific reference to one or more nucleic acids or genes encoding an enzyme associated with or catalyzing, or a protein associated with, the referenced metabolic reaction, reactant or product. Unless otherwise expressly stated herein, those skilled in the art will understand that reference to a reaction also constitutes reference to the reactants and products of the reaction. Similarly, unless otherwise expressly stated herein, reference to a reactant or product also references the reaction, and reference to any of these metabolic constituents also references the gene or genes encoding the enzymes that catalyze or proteins involved in the referenced reaction, reactant or product. Likewise, given the well known fields of metabolic biochemistry, enzymology and genomics, reference herein to a gene or encoding nucleic acid also constitutes a reference to the corresponding encoded enzyme and the reaction it catalyzes or a protein associated with the reaction as well as the reactants and products of the reaction.
As disclosed herein, the product 6-hydroxyhexanoate or 2-ketocyclohexane-1-carboxylate, as well as other intermediates, are carboxylic acids, which can occur in various ionized forms, including fully protonated, partially protonated, and fully deprotonated forms. Accordingly, the suffix “-ate,” or the acid form, can be used interchangeably to describe both the free acid form as well as any deprotonated form, in particular since the ionized form is known to depend on the pH in which the compound is found. It is understood that carboxylate products or intermediates includes ester forms of carboxylate products or pathway intermediates, such as O-carboxylate and S-carboxylate esters. O- and S-carboxylates can include lower alkyl, that is C1 to C6, branched or straight chain carboxylates. Some such O- or S-carboxylates include, without limitation, methyl, ethyl, n-propyl, n-butyl, i-propyl, sec-butyl, and tert-butyl, pentyl, hexyl O- or S-carboxylates, any of which can further possess an unsaturation, providing for example, propenyl, butenyl, pentyl, and hexenyl O- or S-carboxylates. O-carboxylates can be the product of a biosynthetic pathway. Exemplary O-carboxylates accessed via biosynthetic pathways can include, without limitation, methyl 6-hydroxyhexanoate, ethyl 6-hydroxyhexanoate, and n-propyl 6-hydroxyhexanoate. Other biosynthetically accessible O-carboxylates can include medium to long chain groups, that is C7-C22, O-carboxylate esters derived from fatty alcohols, such heptyl, octyl, nonyl, decyl, undecyl, lauryl, tridecyl, myristyl, pentadecyl, cetyl, palmitolyl, heptadecyl, stearyl, nonadecyl, arachidyl, heneicosyl, and behenyl alcohols, any one of which can be optionally branched and/or contain unsaturations. O-carboxylate esters can also be accessed via a biochemical or chemical process, such as esterification of a free carboxylic acid product or transesterification of an O- or S-carboxylate. S-carboxylates are exemplified by CoA S-esters, cysteinyl S-esters, alkylthioesters, and various aryl and heteroaryl thioesters.
The non-naturally occurring microbial organisms of the invention can be produced by introducing expressible nucleic acids encoding one or more of the enzymes or proteins participating in one or more caprolactone biosynthetic pathways. Depending on the host microbial organism chosen for biosynthesis, nucleic acids for some or all of a particular caprolactone biosynthetic pathway can be expressed. For example, if a chosen host is deficient in one or more enzymes or proteins for a desired biosynthetic pathway, then expressible nucleic acids for the deficient enzyme(s) or protein(s) are introduced into the host for subsequent exogenous expression. Alternatively, if the chosen host exhibits endogenous expression of some pathway genes, but is deficient in others, then an encoding nucleic acid is needed for the deficient enzyme(s) or protein(s) to achieve caprolactone biosynthesis. Thus, a non-naturally occurring microbial organism of the invention can be produced by introducing exogenous enzyme or protein activities to obtain a desired biosynthetic pathway or a desired biosynthetic pathway can be obtained by introducing one or more exogenous enzyme or protein activities that, together with one or more endogenous enzymes or proteins, produces a desired product such as caprolactone.
Host microbial organisms can be selected from, and the non-naturally occurring microbial organisms generated in, for example, bacteria, yeast, fungus or any of a variety of other microorganisms applicable or suitable to fermentation processes. Exemplary bacteria include any species selected from the order Enterobacteriales, family Enterobacteriaceae, including the genera Escherichia and Klebsiella; the order Aeromonadales, family Succinivibrionaceae, including the genus Anaerobiospirillum; the order Pasteurellales, family Pasteurellaceae, including the genera Actinobacillus and Mannheimia; the order Rhizobiales, family Bradyrhizobiaceae, including the genus Rhizobium; the order Bacillales, family Bacillaceae, including the genus Bacillus; the order Actinomycetales, families Corynebacteriaceae and Streptomycetaceae, including the genus Corynebacterium and the genus Streptomyces, respectively; order Rhodospirillales, family Acetobacteraceae, including the genus Gluconobacter; the order Sphingomonadales, family Sphingomonadaceae, including the genus Zymomonas; the order Lactobacillales, families Lactobacillaceae and Streptococcaceae, including the genus Lactobacillus and the genus Lactococcus, respectively; the order Clostridiales, family Clostridiaceae, genus Clostridium; and the order Pseudomonadales, family Pseudomonadaceae, including the genus Pseudomonas. Non-limiting species of host bacteria include Escherichia coli, Klebsiella oxytoca, Anaerobiospirillum succiniciproducens, Actinobacillus succinogenes, Mannheimia succiniciproducens, Rhizobium etli, Bacillus subtilis, Corynebacterium glutamicum, Gluconobacter oxydans, Zymomonas mobilis, Lactococcus lactis, Lactobacillus plantarum, Streptomyces coelicolor, Clostridium acetobutylicum, Pseudomonas fluorescens, and Pseudomonas putida.
Similarly, exemplary species of yeast or fungi species include any species selected from the order Saccharomycetales, family Saccaromycetaceae, including the genera Saccharomyces, Kluyveromyces and Pichia; the order Saccharomycetales, family Dipodascaceae, including the genus Yarrowia; the order Schizosaccharomycetales, family Schizosaccaromycetaceae, including the genus Schizosaccharomyces; the order Eurotiales, family Trichocomaceae, including the genus Aspergillus; and the order Mucorales, family Mucoraceae, including the genus Rhizopus. Non-limiting species of host yeast or fungi include Saccharomyces cerevisiae, Schizosaccharomyces pombe, Kluyveromyces lactis, Kluyveromyces marxianus, Aspergillus terreus, Aspergillus niger, Pichia pastoris, Rhizopus arrhizus, Rhizopus oryzae, Yarrowia lipolytica, and the like. E. coli is a particularly useful host organism since it is a well characterized microbial organism suitable for genetic engineering. Other particularly useful host organisms include yeast such as Saccharomyces cerevisiae. It is understood that any suitable microbial host organism can be used to introduce metabolic and/or genetic modifications to produce a desired product.
Depending on the caprolactone biosynthetic pathway constituents of a selected host microbial organism, the non-naturally occurring microbial organisms of the invention will include at least one exogenously expressed caprolactone pathway-encoding nucleic acid and up to all encoding nucleic acids for one or more caprolactone biosynthetic pathways. For example, caprolactone biosynthesis can be established in a host deficient in a pathway enzyme or protein through exogenous expression of the corresponding encoding nucleic acid. In a host deficient in all enzymes or proteins of a caprolactone pathway, exogenous expression of all enzyme or proteins in the pathway can be included, although it is understood that all enzymes or proteins of a pathway can be expressed even if the host contains at least one of the pathway enzymes or proteins. For example, exogenous expression of all enzymes or proteins in a pathway for production of caprolactone can be included, such as an adipyl-CoA reductase, an adipate semialdehyde reductase, a 6-hydroxyhexanoyl-CoA transferase or synthetase, and a 6-hydroxyhexanoyl-CoA cyclase.
Given the teachings and guidance provided herein, those skilled in the art will understand that the number of encoding nucleic acids to introduce in an expressible form will, at least, parallel the caprolactone pathway deficiencies of the selected host microbial organism. Therefore, a non-naturally occurring microbial organism of the invention can have one, two, three, four, five, six, seven up to all nucleic acids encoding the enzymes or proteins constituting a caprolactone biosynthetic pathway disclosed herein. In some embodiments, the non-naturally occurring microbial organisms also can include other genetic modifications that facilitate or optimize caprolactone biosynthesis or that confer other useful functions onto the host microbial organism. One such other functionality can include, for example, augmentation of the synthesis of one or more of the caprolactone pathway precursors such as adipyl-CoA, adipate, adipate semialdehyde, 4-hydroxybutyryl-CoA, cyclohexanone, or pimeloyl-CoA.
Generally, a host microbial organism is selected such that it produces the precursor of a caprolactone pathway, either as a naturally produced molecule or as an engineered product that either provides de novo production of a desired precursor or increased production of a precursor naturally produced by the host microbial organism. For example, adipyl-CoA is produced naturally in a host organism such as E. coli. A host organism can be engineered to increase production of a precursor, as disclosed herein. In addition, a microbial organism that has been engineered to produce a desired precursor can be used as a host organism and further engineered to express enzymes or proteins of a caprolactone pathway.
In some embodiments, a non-naturally occurring microbial organism of the invention is generated from a host that contains the enzymatic capability to synthesize caprolactone. In this specific embodiment it can be useful to increase the synthesis or accumulation of a caprolactone pathway product to, for example, drive caprolactone pathway reactions toward caprolactone production. Increased synthesis or accumulation can be accomplished by, for example, overexpression of nucleic acids encoding one or more of the above-described caprolactone pathway enzymes or proteins. Overexpression of the enzyme or enzymes and/or protein or proteins of the caprolactone pathway can occur, for example, through exogenous expression of the endogenous gene or genes, or through exogenous expression of the heterologous gene or genes. Therefore, naturally occurring organisms can be readily generated to be non-naturally occurring microbial organisms of the invention, for example, producing caprolactone, through overexpression of one, two, three, four, five, six, seven, that is, up to all nucleic acids encoding caprolactone biosynthetic pathway enzymes or proteins. In addition, a non-naturally occurring organism can be generated by mutagenesis of an endogenous gene that results in an increase in activity of an enzyme in the caprolactone biosynthetic pathway.
In particularly useful embodiments, exogenous expression of the encoding nucleic acids is employed. Exogenous expression confers the ability to custom tailor the expression and/or regulatory elements to the host and application to achieve a desired expression level that is controlled by the user. However, endogenous expression also can be utilized in other embodiments such as by removing a negative regulatory effector or induction of the gene's promoter when linked to an inducible promoter or other regulatory element. Thus, an endogenous gene having a naturally occurring inducible promoter can be up-regulated by providing the appropriate inducing agent, or the regulatory region of an endogenous gene can be engineered to incorporate an inducible regulatory element, thereby allowing the regulation of increased expression of an endogenous gene at a desired time. Similarly, an inducible promoter can be included as a regulatory element for an exogenous gene introduced into a non-naturally occurring microbial organism.
It is understood that, in methods of the invention, any of the one or more exogenous nucleic acids can be introduced into a microbial organism to produce a non-naturally occurring microbial organism of the invention. The nucleic acids can be introduced so as to confer, for example, a caprolactone biosynthetic pathway onto the microbial organism. Alternatively, encoding nucleic acids can be introduced to produce an intermediate microbial organism having the biosynthetic capability to catalyze some of the required reactions to confer caprolactone biosynthetic capability. For example, a non-naturally occurring microbial organism having a caprolactone biosynthetic pathway can comprise at least two exogenous nucleic acids encoding desired enzymes or proteins, such as the combination of adipyl-CoA reductase and a 6-hydroxyhexanoate cyclase, or alternatively a 6-hydroxyhexanoate kinase and a 6-hydroxyhexanoyl phosphate cyclase, or alternatively a 3,6-dihydroxyhexanoyl-CoA dehydratase and a 6-hydroxyhex-2-enoyl-CoA reductase, or alternatively a cyclohexane-1,2-diol dehydratase and a cyclohexanone monooxygenase, and the like. Thus, it is understood that any combination of two or more enzymes or proteins of a biosynthetic pathway can be included in a non-naturally occurring microbial organism of the invention. Similarly, it is understood that any combination of three or more enzymes or proteins of a biosynthetic pathway can be included in a non-naturally occurring microbial organism of the invention, for example, an adipyl-CoA reductase, an adipate semialdehyde reductase and a 6-hydroxyhexanoate cyclase, or alternatively an adipate semialdehyde reductase, a 6-hydroxyhexanoyl-CoA transferase, and a 6-hydroxyhexanoyl-CoA cyclase, or alternatively a 3-oxo-6-hydroxyhexanoyl-CoA reductase, a 6-hydroxyhex-2-enoyl-CoA reductase and a 6-hydroxyhexanoate cyclase, and so forth, as desired, so long as the combination of enzymes and/or proteins of the desired biosynthetic pathway results in production of the corresponding desired product. Similarly, any combination of four, five, six, seven or more enzymes or proteins of a biosynthetic pathway as disclosed herein can be included in a non-naturally occurring microbial organism of the invention, as desired, so long as the combination of enzymes and/or proteins of the desired biosynthetic pathway results in production of the corresponding desired product.
In addition to the biosynthesis of caprolactone as described herein, the non-naturally occurring microbial organisms and methods of the invention also can be utilized in various combinations with each other and with other microbial organisms and methods well known in the art to achieve product biosynthesis by other routes. For example, one alternative to produce caprolactone other than use of the caprolactone producers is through addition of another microbial organism capable of converting a caprolactone pathway intermediate to caprolactone. One such procedure includes, for example, the fermentation of a microbial organism that produces a caprolactone pathway intermediate. The caprolactone pathway intermediate can then be used as a substrate for a second microbial organism that converts the caprolactone pathway intermediate to caprolactone. The caprolactone pathway intermediate can be added directly to another culture of the second organism or the original culture of the caprolactone pathway intermediate producers can be depleted of these microbial organisms by, for example, cell separation, and then subsequent addition of the second organism to the fermentation broth can be utilized to produce the final product without intermediate purification steps.
In other embodiments, the non-naturally occurring microbial organisms and methods of the invention can be assembled in a wide variety of subpathways to achieve biosynthesis of, for example, caprolactone. In these embodiments, biosynthetic pathways for a desired product of the invention can be segregated into different microbial organisms, and the different microbial organisms can be co-cultured to produce the final product. In such a biosynthetic scheme, the product of one microbial organism is the substrate for a second microbial organism until the final product is synthesized. For example, the biosynthesis of caprolactone can be accomplished by constructing a microbial organism that contains biosynthetic pathways for conversion of one pathway intermediate to another pathway intermediate or the product. Alternatively, caprolactone also can be biosynthetically produced from microbial organisms through co-culture or co-fermentation using two organisms in the same vessel, where the first microbial organism produces a caprolactone intermediate and the second microbial organism converts the intermediate to caprolactone.
Given the teachings and guidance provided herein, those skilled in the art will understand that a wide variety of combinations and permutations exist for the non-naturally occurring microbial organisms and methods of the invention together with other microbial organisms, with the co-culture of other non-naturally occurring microbial organisms having subpathways and with combinations of other chemical and/or biochemical procedures well known in the art to produce caprolactone.
Sources of encoding nucleic acids for a caprolactone pathway enzyme or protein can include, for example, any species where the encoded gene product is capable of catalyzing the referenced reaction. Such species include both prokaryotic and eukaryotic organisms including, but not limited to, bacteria, including archaea and eubacteria, and eukaryotes, including yeast, plant, insect, animal, and mammal, including human. Exemplary species for such sources include, for example, Escherichia coli, Acinetobacter sp. NCIMB9871, Acetobacter aceti, Acidaminococcus fermentans, Acinetobacter baylyi, Acinetobacter calcoaceticus, Acinetobacter sp NCIMB9871, Acinetobacter sp. ADP1, Acinetobacter sp. NCIMB9871, Acinetobacter sp. SE19, Acinetobacter sp. strain M-1, Actinobacillus succinogenes, Aeropyrum pernix, Allochromatium vinosum DSM 180, Anaerobiospirillum succiniciproducens, Aquifex aeolicus, Arabidopsis thaliana, Archaeoglobus fulgidus, Aromatoleum aromaticum EbN1, Arthrobacter sp. BP2, Ascaris suum, Aspergillus nidulans, Aspergillus terreus NIH2624, Azoarcus sp. Strain 22Lin, Azoarcus sp. T, Azotobacter vinelandii DJ, Bacillus cereus, Bacillus megaterium, Bacillus megaterium WSH-002, Bacillus sphaericus, Bacillus subtilis, Balnearium lithotrophicum, Bos taurus, Brevibacerium sp. HCU, Burkholderia ambifaria AMD, Burkholderia phymatum, butyrate-producing bacterium L2-50, butyrate-producing bacterium L2-50, Campylobacter curvus 525.92, Campylobacter jejuni, Candida albicans, Candida tropicalis, Carboxydothermus hydrogenoformans, Chlorobium phaeobacteroides DSM 266, Chlorobium limicola, Chlorobium tepidum, Citrobacter feundii, Citrobacter youngae, Citrobacter youngae ATCC 29220, Clostridium acetobutylicum, Clostridium beijerinckii, Clostridium botulinum, Clostridium butyricum, Clostridium carboxidivorans P7, Clostridium carboxidivorans P7, Clostridium cellulolyticum H10, Clostridium kluyveri, Clostridium kluyveri DSM 555, Clostridium novyi NT, Clostridium pasteurianum, Clostridium propionicum, Clostridium saccharoperbutylacetonicum, Clostridium symbiosum, Comamonas testosterone, Corynebacterium glutamicum, Cupriavidus taiwanensis, Cyanobium PCC7001, Desulfarculus baarsii DSM 2075, Desulfovibrio africanus, DesulfoVibrio desulfuricans G20, Desulfovibrio desulfuricans subsp. desulfuricans str. A TCC 27774, Desulfovibrio fructosovorans JJ, Desulfovibrio vulgaris str. Hildenborough, Dictyostelium discoideum AX4, Escherichia coli K12 sp. MG1655, Eubacterium rectale, Fusobacterium nucleatum, Geobacillus kaustophilus, Geobacillus thermoglucosidasius, Geobacter metallireducens GS-15, Geobacter sulfurreducens, Haemophilus influenza, Haloarcula marismortui, Helicobacter pylori, Helicobacter pylori 26695, Homo sapiens, Hydrogenobacter thermophilus, Klebsiella oxytoca, Klebsiella pneumoniae, Klebsiella pneumoniae subsp. rhinoscleromatis, Lactobacillus collinoides, Leuconostoc mesenteroides, Mannheimia succiniciproducens, Metallosphaera sedula, Methanosarcina thermophila, Methanothermobacter thermautotrophicus, Methylobacterium extorquens, Moorella thermoacetica, Mus musculus, Mycobacterium avium subsp. paratuberculosis K-10, Mycobacterium bovis BCG, Mycobacterium marinum M, Mycobacterium smegmatis, Mycobacterium smegmatis MC2 155, Mycobacterium tuberculosis, Neurospora crassa, Nocardia farcinica IFM 10152, Nocardia iowensis, Nostoc sp. PCC 7120, Oryza sativa, Paracoccus denitrificans, Pelobacter carbinolicus DSM 2380, Pelotomaculum thermopropionicum, Penicillium chrysogenum. Porphyromonas gingivalis, Pseudomonas aeruginosa PA 01, Pseudomonas fluorescens, Pseudomonas knackmussii, Pseudomonas knackmussii (B13), Pseudomonas mendocina, Pseudomonas putida, Pseudomonas sp, Pyrobaculum aerophilum str. IM2, Ralstonia eutropha, Ralstonia eutropha H16, Ralstonia metallidurans, Ralstonia metallireducens, Rattus norvegicus, Rhizobium leguminosarum, Rhodobacter capsulatus, Rhodobacter sphaeroides, Rhodococcus sp. Phi1, Rhodococcus sp. Phi2, Rhodopseudomonas palustris, Rhodopseudomonas palustris CGA009, Rhodospirillum rubrum, Roseburia intestinalis, Roseburia inulinivorans, Roseburia sp. A2-183, Saccharomyces cerevisiae, Salmonella enteric, Salmonella enterica subsp. arizonae serovar, Salmonella typhimurium, Salmonella typhimurium LT2, Schizosaccharomyces pombe, Sinorhizobium fredii, Sordaria macrospora, Staphylococcus aureus, Streptomyces coelicolor, Streptomyces griseus subsp. griseus NBRC 13350, Sulfolobus acidocalarius, Sulfolobus solfataricus, Sulfolobus sp. strain 7, Sulfolobus tokodaii, Sulfurihydrogenibium subterraneum, Sulfurimonas denitrificans, Synechocystis str. PCC 6803, Syntrophus aciditrophicus, Thauera aromatic, Thermocrinis albus, Thermoproteus neutrophilus, Thermotoga maritima, Thermus thermophilus, Thiobacillus denitrificans, Thiocapsa roseopersicina, Trichomonas vaginalis G3, Trypanosoma brucei, Tsukamurella paurometabola DSM 20162, Xanthobacter flavus, Yarrowia lipolytica, Yersinia intermedia, Yersinia intermedia A TCC 29909, Zea mays, Zoogloea ramigera, Zymomonas mobilis, as well as other exemplary species disclosed herein or available as source organisms for corresponding genes. However, with the complete genome sequence available for now more than 550 species (with more than half of these available on public databases such as the NCBI), including 395 microorganism genomes and a variety of yeast, fungi, plant, and mammalian genomes, the identification of genes encoding the requisite caprolactone biosynthetic activity for one or more genes in related or distant species, including for example, homologues, orthologs, paralogs and nonorthologous gene displacements of known genes, and the interchange of genetic alterations between organisms is routine and well known in the art. Accordingly, the metabolic alterations allowing biosynthesis of caprolactone described herein with reference to a particular organism such as E. coli can be readily applied to other microorganisms, including prokaryotic and eukaryotic organisms alike. Given the teachings and guidance provided herein, those skilled in the art will know that a metabolic alteration exemplified in one organism can be applied equally to other organisms.
In some instances, such as when an alternative caprolactone biosynthetic pathway exists in an unrelated species, caprolactone biosynthesis can be conferred onto the host species by, for example, exogenous expression of a paralog or paralogs from the unrelated species that catalyzes a similar, yet non-identical metabolic reaction to replace the referenced reaction. Because certain differences among metabolic networks exist between different organisms, those skilled in the art will understand that the actual gene usage between different organisms may differ. However, given the teachings and guidance provided herein, those skilled in the art also will understand that the teachings and methods of the invention can be applied to all microbial organisms using the cognate metabolic alterations to those exemplified herein to construct a microbial organism in a species of interest that will synthesize caprolactone.
Methods for constructing and testing the expression levels of a non-naturally occurring caprolactone-producing host can be performed, for example, by recombinant and detection methods well known in the art. Such methods can be found described in, for example, Sambrook et al., Molecular Cloning: A Laboratory Manual, Third Ed., Cold Spring Harbor Laboratory, New York (2001); and Ausubel et al., Current Protocols in Molecular Biology, John Wiley and Sons, Baltimore, Md. (1999).
Exogenous nucleic acid sequences involved in a pathway for production of caprolactone can be introduced stably or transiently into a host cell using techniques well known in the art including, but not limited to, conjugation, electroporation, chemical transformation, transduction, transfection, and ultrasound transformation. For exogenous expression in E. coli or other prokaryotic cells, some nucleic acid sequences in the genes or cDNAs of eukaryotic nucleic acids can encode targeting signals such as an N-terminal mitochondrial or other targeting signal, which can be removed before transformation into prokaryotic host cells, if desired. For example, removal of a mitochondrial leader sequence led to increased expression in E. coli (Hoffmeister et al., J. Biol. Chem. 280:4329-4338 (2005)). For exogenous expression in yeast or other eukaryotic cells, genes can be expressed in the cytosol without the addition of leader sequence, or can be targeted to mitochondrion or other organelles, or targeted for secretion, by the addition of a suitable targeting sequence such as a mitochondrial targeting or secretion signal suitable for the host cells. Thus, it is understood that appropriate modifications to a nucleic acid sequence to remove or include a targeting sequence can be incorporated into an exogenous nucleic acid sequence to impart desirable properties. Furthermore, genes can be subjected to codon optimization with techniques well known in the art to achieve optimized expression of the proteins.
An expression vector or vectors can be constructed to include one or more caprolactone biosynthetic pathway encoding nucleic acids as exemplified herein operably linked to expression control sequences functional in the host organism. Expression vectors applicable for use in the microbial host organisms of the invention include, for example, plasmids, phage vectors, viral vectors, episomes and artificial chromosomes, including vectors and selection sequences or markers operable for stable integration into a host chromosome. Additionally, the expression vectors can include one or more selectable marker genes and appropriate expression control sequences. Selectable marker genes also can be included that, for example, provide resistance to antibiotics or toxins, complement auxotrophic deficiencies, or supply critical nutrients not in the culture media. Expression control sequences can include constitutive and inducible promoters, transcription enhancers, transcription terminators, and the like which are well known in the art. When two or more exogenous encoding nucleic acids are to be co-expressed, both nucleic acids can be inserted, for example, into a single expression vector or in separate expression vectors. For single vector expression, the encoding nucleic acids can be operationally linked to one common expression control sequence or linked to different expression control sequences, such as one inducible promoter and one constitutive promoter. The transformation of exogenous nucleic acid sequences involved in a metabolic or synthetic pathway can be confirmed using methods well known in the art. Such methods include, for example, nucleic acid analysis such as Northern blots or polymerase chain reaction (PCR) amplification of mRNA, or immunoblotting for expression of gene products, or other suitable analytical methods to test the expression of an introduced nucleic acid sequence or its corresponding gene product. It is understood by those skilled in the art that the exogenous nucleic acid is expressed in a sufficient amount to produce the desired product, and it is further understood that expression levels can be optimized to obtain sufficient expression using methods well known in the art and as disclosed herein.
In one embodiment, the invention provides a method for producing caprolactone, by culturing the non-naturally occurring microbial organism as described herein under conditions and for a sufficient period of time to produce caprolactone. In some embodiments, the method includes a non-naturally occurring microbial organism having a caprolactone pathway, wherein the microbial organism includes at least one exogenous nucleic acid encoding a caprolactone pathway enzyme expressed in a sufficient amount to produce caprolactone. In some aspects of the invention, the caprolactone pathway includes a pathway selected from: (1) 1A, 1B, 1C and 1D; (2) 1E, 1B, 1C and 1D; (3) 1F, 1A, 1B, 1C and 1D; (4) 1F, 1E, 1B, 1C and 1D; (5) 1A, 1B and 1G; (6) 1E, 1B and 1G; (7) 1F, 1A, 1B and 1G; (8) 1F, 1E, 1B and 1G; (9) 1A, 1B, 1C, 1J and 1I; (10) 1E, 1B, 1C, 1J and 1I; (11) 1F, 1A, 1B, 1C, 1J and 1I; (12) 1F, 1E, 1B, 1C, 1J and 1I; (13) 1A, 1B, 1H and 1I; (14) 1E, 1B, 1H and 1I; (15) 1F, 1A, 1B, 1H and 1I; (16) 1F, 1E, 1B, 1H and 1I; (17) 2A, 2B, 2C, 2D, 2E and 2F; (18) 2A, 2B, 2C, 2D and 2G; (19) 2A, 2B, 2C, 2D, 2E, 2J and 2I; (20) 2A, 2B, 2C, 2D, 2H and 2I; (2I) 4A, 4B, 4C, 4D and 3A; and (22) 5A, 5B, 5C an 3A, wherein 1A is an adipyl-CoA reductase, wherein 1B is an adipate semialdehyde reductase, wherein 1C is a 6-hydroxyhexanoyl-CoA transferase or a 6-hydroxyhexanoyl-CoA synthetase, wherein 1D is a 6-hydroxyhexanoyl-CoA cyclase or spontaneous cyclization, wherein 1E is an adipate reductase, wherein 1F is an adipyl-CoA transferase, an adipyl-CoA synthetase or an adipyl-CoA hydrolase, wherein 1G is a 6-hydroxyhexanoate cyclase, wherein 1H is a 6-hydroxyhexanoate kinase, wherein 1I is a 6-hydroxyhexanoyl phosphate cyclase or spontaneous cyclization, wherein 1J is a phosphotrans-6-hydroxyhexanoylase, wherein 2A is a 4-hydroxybutyryl-CoA:acetyl-CoA acyltransferase, wherein 2B is a 3-oxo-6-hydroxyhexanoyl-CoA reductase, wherein 2C is a 3,6-dihydroxyhexanoyl-CoA dehydratase, wherein 2D is a 6-hydroxyhex-2-enoyl-CoA reductase, wherein 2E is a 6-hydroxyhexanoyl-CoA transferase, a 6-hydroxyhexanoyl-CoA synthetase or a 6-hydroxyhexanoyl-CoA hydrolase, wherein 2F is a 6-hydroxyhexanoate cyclase, wherein 2G is a 6-hydroxyhexanoyl-CoA cyclase or spontaneous cyclization, wherein 2H is a phosphotrans-6-hydroxyhexanoylase, wherein 2I is a 6-hydroxyhexanoyl phosphate cyclase or spontaneous cyclization, wherein 2J is a 6-hydroxyhexanoate kinase, wherein 3A is a cyclohexanone monooxygenase, wherein 4A is an adipate semialdehyde dehydratase, wherein 4B is a cyclohexane-1,2-dione reductase, wherein 4C is a 2-hydroxycyclohexanone reductase, wherein 4D is a cyclohexane-1,2-diol dehydratase, wherein 5A is a 2-ketocyclohexane-1-carboxoyl-CoA hydrolase (acting on C—C), wherein 5B is a 2-ketocyclohexane-1-carboxoyl-CoA transferase, a 2-ketocyclohexane-1-carboxoyl-CoA synthetase or a 2-ketocyclohexane-1-carboxoyl-CoA hydrolase, and wherein 5C is a 2-ketocyclohexane-1-carboxylate decarboxylase.
In one embodiment, the invention provides a method for producting caprolactone using a non-naturally occurring microbial organism as described herein, wherein the microbial organism includes two, three, four, five, six or seven exogenous nucleic acids each encoding a caprolactone pathway enzyme. For example, the microbial organism can include exogenous nucleic acids encoding each of the enzymes of at least one of the pathways selected from (1)-(22) as described above.
In one embodiment, the invention provides a method for producting caprolactone using a microbial organism wherein at least one exogenous nucleic acid is a heterologous nucleic acid. In another aspect, the non-naturally occurring microbial organism as disclosed herein is in a substantially anaerobic culture medium.
In one embodiment, the invention provides a method for producing caprolactone wherein the non-naturally occurring microbial organism as disclosed herein further includes (i) a reductive TCA pathway comprising at least one exogenous nucleic acid encoding a reductive TCA pathway enzyme, wherein said at least one exogenous nucleic acid is selected from an ATP-citrate lyase, citrate lyase, a fumarate reductase, and an alpha-ketoglutarate:ferredoxin oxidoreductase; (ii) a reductive TCA pathway comprising at least one exogenous nucleic acid encoding a reductive TCA pathway enzyme, wherein said at least one exogenous nucleic acid is selected from a pyruvate:ferredoxin oxidoreductase, a phosphoenolpyruvate carboxylase, a phosphoenolpyruvate carboxykinase, a CO dehydrogenase, and an H₂hydrogenase; or (iii) at least one exogenous nucleic acid encodes an enzyme selected from a CO dehydrogenase, an H₂hydrogenase, and combinations thereof.
In one embodiment, the invention provides a method for producing caprolactone wherein the non-naturally occurring microbial organism having (i) above, further includes an exogenous nucleic acid encoding an enzyme selected from a pyruvate:ferredoxin oxidoreductase, an aconitase, an isocitrate dehydrogenase, a succinyl-CoA synthetase, a succinyl-CoA transferase, a fumarase, a malate dehydrogenase, an acetate kinase, a phosphotransacetylase, an acetyl-CoA synthetase, an NAD(P)H:ferredoxin oxidoreductase, ferredoxin, and combinations thereof. In another aspect, the non-naturally occurring microbial organism including (ii) as described above further includes an exogenous nucleic acid encoding an enzyme selected from an aconitase, an isocitrate dehydrogenase, a succinyl-CoA synthetase, a succinyl-CoA transferase, a fumarase, a malate dehydrogenase, and combinations thereof.
In one embodiment, the invention provides a method for producing caprolactone wherein the non-naturally occurring microbial organism having (i) as described above further comprises four exogenous nucleic acids encoding an ATP-citrate lyase, citrate lyase, a fumarate reductase, and an alpha-ketoglutarate:ferredoxin oxidoreductase. In one aspect of the invention, the non-naturally occurring microbial organism having (ii) as described above further comprises five exogenous nucleic acids encoding a pyruvate:ferredoxin oxidoreductase, a phosphoenolpyruvate carboxylase, a phosphoenolpyruvate carboxykinase, a CO dehydrogenase, and an H₂hydrogenase. In one aspect of the invention, the non-naturally occurring microbial organism having (iii) as described above further comprises two exogenous nucleic acids encoding a CO dehydrogenase and an H₂hydrogenase.
Suitable purification and/or assays to test for the production of caprolactone can be performed using well known methods. Suitable replicates such as triplicate cultures can be grown for each engineered strain to be tested. For example, product and byproduct formation in the engineered production host can be monitored. The final product and intermediates, and other organic compounds, can be analyzed by methods such as HPLC (High Performance Liquid Chromatography), GC-MS (Gas Chromatography-Mass Spectroscopy) and LC-MS (Liquid Chromatography-Mass Spectroscopy) or other suitable analytical methods using routine procedures well known in the art. The release of product in the fermentation broth can also be tested with the culture supernatant. Byproducts and residual glucose can be quantified by HPLC using, for example, a refractive index detector for glucose and alcohols, and a UV detector for organic acids (Lin et al., Biotechnol. Bioeng. 90:775-779 (2005)), or other suitable assay and detection methods well known in the art. The individual enzyme or protein activities from the exogenous DNA sequences can also be assayed using methods well known in the art.
The caprolactone can be separated from other components in the culture using a variety of methods well known in the art. Such separation methods include, for example, extraction procedures as well as methods that include continuous liquid-liquid extraction, pervaporation, membrane filtration, membrane separation, reverse osmosis, electrodialysis, distillation, crystallization, centrifugation, extractive filtration, ion exchange chromatography, size exclusion chromatography, adsorption chromatography, and ultrafiltration. All of the above methods are well known in the art.
Any of the non-naturally occurring microbial organisms described herein can be cultured to produce and/or secrete the biosynthetic products of the invention. For example, the caprolactone producers can be cultured for the biosynthetic production of caprolactone. Accordingly, in some embodiments, the invention provides culture medium having the caprolactone or caprolactone pathway intermediate described herein. In some aspects, the culture mediums can also be separated from the non-naturally occurring microbial organisms of the invention that produced the caprolactone or caprolactone pathway intermediate. Methods for separating a microbial organism from culture medium are well known in the art. Exemplary methods include filtration, flocculation, precipitation, centrifugation, sedimentation, and the like.
For the production of caprolactone, the recombinant strains are cultured in a medium with carbon source and other essential nutrients. It is sometimes desirable and can be highly desirable to maintain anaerobic conditions in the fermenter to reduce the cost of the overall process. Such conditions can be obtained, for example, by first sparging the medium with nitrogen and then sealing the flasks with a septum and crimp-cap. For strains where growth is not observed anaerobically, microaerobic or substantially anaerobic conditions can be applied by perforating the septum with a small hole for limited aeration. Exemplary anaerobic conditions have been described previously and are well-known in the art. Exemplary aerobic and anaerobic conditions are described, for example, in United State publication 2009/0047719, filed Aug. 10, 2007. Fermentations can be performed in a batch, fed-batch or continuous manner, as disclosed herein. Fermentations can also be conducted in two phases, if desired. The first phase can be aerobic to allow for high growth and therefore high productivity, followed by an anaerobic phase of high caprolactone yields.
If desired, the pH of the medium can be maintained at a desired pH, in particular neutral pH, such as a pH of around 7 by addition of a base, such as NaOH or other bases, or acid, as needed to maintain the culture medium at a desirable pH. The growth rate can be determined by measuring optical density using a spectrophotometer (600 nm), and the glucose uptake rate by monitoring carbon source depletion over time.
The growth medium can include, for example, any carbohydrate source which can supply a source of carbon to the non-naturally occurring microorganism. Such sources include, for example, sugars such as glucose, xylose, arabinose, galactose, mannose, fructose, sucrose and starch. Other sources of carbohydrate include, for example, renewable feedstocks and biomass. Exemplary types of biomasses that can be used as feedstocks in the methods of the invention include cellulosic biomass, hemicellulosic biomass and lignin feedstocks or portions of feedstocks. Such biomass feedstocks contain, for example, carbohydrate substrates useful as carbon sources such as glucose, xylose, arabinose, galactose, mannose, fructose and starch. Given the teachings and guidance provided herein, those skilled in the art will understand that renewable feedstocks and biomass other than those exemplified above also can be used for culturing the microbial organisms of the invention for the production of caprolactone.
In addition to renewable feedstocks such as those exemplified above, the caprolactone microbial organisms of the invention also can be modified for growth on syngas as its source of carbon. In this specific embodiment, one or more proteins or enzymes are expressed in the caprolactone producing organisms to provide a metabolic pathway for utilization of syngas or other gaseous carbon source.
Synthesis gas, also known as syngas or producer gas, is the major product of gasification of coal and of carbonaceous materials such as biomass materials, including agricultural crops and residues. Syngas is a mixture primarily of H₂and CO and can be obtained from the gasification of any organic feedstock, including but not limited to coal, coal oil, natural gas, biomass, and waste organic matter. Gasification is generally carried out under a high fuel to oxygen ratio. Although largely H₂and CO, syngas can also include CO₂and other gases in smaller quantities. Thus, synthesis gas provides a cost effective source of gaseous carbon such as CO and, additionally, CO₂.
The Wood-Ljungdahl pathway catalyzes the conversion of CO and H₂to acetyl-CoA and other products such as acetate. Organisms capable of utilizing CO and syngas also generally have the capability of utilizing CO₂and CO₂/H₂mixtures through the same basic set of enzymes and transformations encompassed by the Wood-Ljungdahl pathway. H₂-dependent conversion of CO₂to acetate by microorganisms was recognized long before it was revealed that CO also could be used by the same organisms and that the same pathways were involved. Many acetogens have been shown to grow in the presence of CO₂and produce compounds such as acetate as long as hydrogen is present to supply the necessary reducing equivalents (see for example, Drake, Acetogenesis, pp. 3-60 Chapman and Hall, New York, (1994)). This can be summarized by the following equation:
2CO₂+4H₂ +nADP+nPi→CH₃COOH+2H₂O+nATP
Hence, non-naturally occurring microorganisms possessing the Wood-Ljungdahl pathway can utilize CO₂and H₂mixtures as well for the production of acetyl-CoA and other desired products.
The Wood-Ljungdahl pathway is well known in the art and consists of 12 reactions which can be separated into two branches: (1) methyl branch and (2) carbonyl branch. The methyl branch converts syngas to methyl-tetrahydrofolate (methyl-THF) whereas the carbonyl branch converts methyl-THF to acetyl-CoA. The reactions in the methyl branch are catalyzed in order by the following enzymes or proteins:ferredoxin oxidoreductase, formate dehydrogenase, formyltetrahydrofolate synthetase, methenyltetrahydrofolate cyclodehydratase, methylenetetrahydrofolate dehydrogenase and methylenetetrahydrofolate reductase. The reactions in the carbonyl branch are catalyzed in order by the following enzymes or proteins: methyltetrahydrofolate:corrinoid protein methyltransferase (for example, AcsE), corrinoid iron-sulfur protein, nickel-protein assembly protein (for example, AcsF), ferredoxin, acetyl-CoA synthase, carbon monoxide dehydrogenase and nickel-protein assembly protein (for example, CooC). Following the teachings and guidance provided herein for introducing a sufficient number of encoding nucleic acids to generate a caprolactone pathway, those skilled in the art will understand that the same engineering design also can be performed with respect to introducing at least the nucleic acids encoding the Wood-Ljungdahl enzymes or proteins absent in the host organism. Therefore, introduction of one or more encoding nucleic acids into the microbial organisms of the invention such that the modified organism contains the complete Wood-Ljungdahl pathway will confer syngas utilization ability.
Additionally, the reductive (reverse) tricarboxylic acid cycle coupled with carbon monoxide dehydrogenase and/or hydrogenase activities can also be used for the conversion of CO, CO₂and/or H₂to acetyl-CoA and other products such as acetate. Organisms capable of fixing carbon via the reductive TCA pathway can utilize one or more of the following enzymes: ATP citrate-lyase, citrate lyase, aconitase, isocitrate dehydrogenase, alpha-ketoglutarate:ferredoxin oxidoreductase, succinyl-CoA synthetase, succinyl-CoA transferase, fumarate reductase, fumarase, malate dehydrogenase, NAD(P)H:ferredoxin oxidoreductase, carbon monoxide dehydrogenase, and hydrogenase. Specifically, the reducing equivalents extracted from CO and/or H₂by carbon monoxide dehydrogenase and hydrogenase are utilized to fix CO₂via the reductive TCA cycle into acetyl-CoA or acetate. Acetate can be converted to acetyl-CoA by enzymes such as acetyl-CoA transferase, acetate kinase/phosphotransacetylase, and acetyl-CoA synthetase. Acetyl-CoA can be converted to the caprolactone precursors, glyceraldehyde-3-phosphate, phosphoenolpyruvate, and pyruvate, by pyruvate:ferredoxin oxidoreductase and the enzymes of gluconeogenesis. Following the teachings and guidance provided herein for introducing a sufficient number of encoding nucleic acids to generate a caprolactone pathway, those skilled in the art will understand that the same engineering design also can be performed with respect to introducing at least the nucleic acids encoding the reductive TCA pathway enzymes or proteins absent in the host organism. Therefore, introduction of one or more encoding nucleic acids into the microbial organisms of the invention such that the modified organism contains a reductive TCA pathway can confer syngas utilization ability.
Accordingly, given the teachings and guidance provided herein, those skilled in the art will understand that a non-naturally occurring microbial organism can be produced that secretes the biosynthesized compounds of the invention when grown on a carbon source such as a carbohydrate. Such compounds include, for example, caprolactone and any of the intermediate metabolites in the caprolactone pathway. All that is required is to engineer in one or more of the required enzyme or protein activities to achieve biosynthesis of the desired compound or intermediate including, for example, inclusion of some or all of the caprolactone biosynthetic pathways. Accordingly, the invention provides a non-naturally occurring microbial organism that produces and/or secretes caprolactone when grown on a carbohydrate or other carbon source and produces and/or secretes any of the intermediate metabolites shown in the caprolactone pathway when grown on a carbohydrate or other carbon source. The caprolactone producing microbial organisms of the invention can initiate synthesis from an intermediate, for example, 6-hydroxyhexanoate, 6-hydroxyhexanoyl-CoA, 6-hydroxyhexanoyl phosphate, 3-oxo-6-hydroxy hexanoyl-CoA, 3,6-dihydroxy hexanoyl-CoA, 6-hydroxyhex-2-enoyl-CoA, cyclohexanone, cyclohexane-1,2-dione, 2-hydroxycyclohexanone, cyclohexane-1,2-diol, 2-ketocyclohexane-1-carboxyoyl-CoA, or 2-ketocyclohexane-1-carboxylate.
The non-naturally occurring microbial organisms of the invention are constructed using methods well known in the art as exemplified herein to exogenously express at least one nucleic acid encoding a caprolactone pathway enzyme or protein in sufficient amounts to produce caprolactone. It is understood that the microbial organisms of the invention are cultured under conditions sufficient to produce caprolactone. Following the teachings and guidance provided herein, the non-naturally occurring microbial organisms of the invention can achieve biosynthesis of caprolactone resulting in intracellular concentrations between about 0.1-200 mM or more. Generally, the intracellular concentration of caprolactone is between about 3-150 mM, particularly between about 5-125 mM and more particularly between about 8-100 mM, including about 10 mM, 20 mM, 50 mM, 80 mM, or more. Intracellular concentrations between and above each of these exemplary ranges also can be achieved from the non-naturally occurring microbial organisms of the invention.
In some embodiments, culture conditions include anaerobic or substantially anaerobic growth or maintenance conditions. Exemplary anaerobic conditions have been described previously and are well known in the art. Exemplary anaerobic conditions for fermentation processes are described herein and are described, for example, in U.S. publication 2009/0047719, filed Aug. 10, 2007. Any of these conditions can be employed with the non-naturally occurring microbial organisms as well as other anaerobic conditions well known in the art. Under such anaerobic or substantially anaerobic conditions, the caprolactone producers can synthesize caprolactone at intracellular concentrations of 5-10 mM or more as well as all other concentrations exemplified herein. It is understood that, even though the above description refers to intracellular concentrations, caprolactone producing microbial organisms can produce caprolactone intracellularly and/or secrete the product into the culture medium.
In addition to the culturing and fermentation conditions disclosed herein, growth condition for achieving biosynthesis of caprolactone can include the addition of an osmoprotectant to the culturing conditions. In certain embodiments, the non-naturally occurring microbial organisms of the invention can be sustained, cultured or fermented as described herein in the presence of an osmoprotectant. Briefly, an osmoprotectant refers to a compound that acts as an osmolyte and helps a microbial organism as described herein survive osmotic stress. Osmoprotectants include, but are not limited to, betaines, amino acids, and the sugar trehalose. Non-limiting examples of such are glycine betaine, praline betaine, dimethylthetin, dimethylslfonioproprionate, 3-dimethylsulfonio-2-methylproprionate, pipecolic acid, dimethylsulfonioacetate, choline, L-carnitine and ectoine. In one aspect, the osmoprotectant is glycine betaine. It is understood to one of ordinary skill in the art that the amount and type of osmoprotectant suitable for protecting a microbial organism described herein from osmotic stress will depend on the microbial organism used. The amount of osmoprotectant in the culturing conditions can be, for example, no more than about 0.1 mM, no more than about 0.5 mM, no more than about 1.0 mM, no more than about 1.5 mM, no more than about 2.0 mM, no more than about 2.5 mM, no more than about 3.0 mM, no more than about 5.0 mM, no more than about 7.0 mM, no more than about 10 mM, no more than about 50 mM, no more than about 100 mM or no more than about 500 mM.
In some embodiments, the carbon feedstock and other cellular uptake sources such as phosphate, ammonia, sulfate, chloride and other halogens can be chosen to alter the isotopic distribution of the atoms present in caprolactone or any caprolactone pathway intermediate. The various carbon feedstock and other uptake sources enumerated above will be referred to herein, collectively, as “uptake sources.” Uptake sources can provide isotopic enrichment for any atom present in the product caprolactone or caprolactone pathway intermediate, or for side products generated in reactions diverging away from a caprolactone pathway. Isotopic enrichment can be achieved for any target atom including, for example, carbon, hydrogen, oxygen, nitrogen, sulfur, phosphorus, chloride or other halogens.
In some embodiments, the uptake sources can be selected to alter the carbon-12, carbon-13, and carbon-14 ratios. In some embodiments, the uptake sources can be selected to alter the oxygen-16, oxygen-17, and oxygen-18 ratios. In some embodiments, the uptake sources can be selected to alter the hydrogen, deuterium, and tritium ratios. In some embodiments, the uptake sources can be selected to alter the nitrogen-14 and nitrogen-15 ratios. In some embodiments, the uptake sources can be selected to alter the sulfur-32, sulfur-33, sulfur-34, and sulfur-35 ratios. In some embodiments, the uptake sources can be selected to alter the phosphorus-31, phosphorus-32, and phosphorus-33 ratios. In some embodiments, the uptake sources can be selected to alter the chlorine-35, chlorine-36, and chlorine-37 ratios.
In some embodiments, the isotopic ratio of a target atom can be varied to a desired ratio by selecting one or more uptake sources. An uptake source can be derived from a natural source, as found in nature, or from a man-made source, and one skilled in the art can select a natural source, a man-made source, or a combination thereof, to achieve a desired isotopic ratio of a target atom. An example of a man-made uptake source includes, for example, an uptake source that is at least partially derived from a chemical synthetic reaction. Such isotopically enriched uptake sources can be purchased commercially or prepared in the laboratory and/or optionally mixed with a natural source of the uptake source to achieve a desired isotopic ratio. In some embodiments, a target atom isotopic ratio of an uptake source can be achieved by selecting a desired origin of the uptake source as found in nature. For example, as discussed herein, a natural source can be a biobased derived from or synthesized by a biological organism or a source such as petroleum-based products or the atmosphere. In some such embodiments, a source of carbon, for example, can be selected from a fossil fuel-derived carbon source, which can be relatively depleted of carbon-14, or an environmental or atmospheric carbon source, such as CO₂, which can possess a larger amount of carbon-14 than its petroleum-derived counterpart.
The unstable carbon isotope carbon-14 or radiocarbon makes up for roughly 1 in 10¹²carbon atoms in the earth's atmosphere and has a half-life of about 5700 years. The stock of carbon is replenished in the upper atmosphere by a nuclear reaction involving cosmic rays and ordinary nitrogen (¹⁴N). Fossil fuels contain no carbon-14, as it decayed long ago. Burning of fossil fuels lowers the atmospheric carbon-14 fraction, the so-called “Suess effect”.
Methods of determining the isotopic ratios of atoms in a compound are well known to those skilled in the art. Isotopic enrichment is readily assessed by mass spectrometry using techniques known in the art such as accelerated mass spectrometry (AMS), Stable Isotope Ratio Mass Spectrometry (SIRMS) and Site-Specific Natural Isotopic Fractionation by Nuclear Magnetic Resonance (SNIF-NMR). Such mass spectral techniques can be integrated with separation techniques such as liquid chromatography (LC), high performance liquid chromatography (HPLC) and/or gas chromatography, and the like.
In the case of carbon, ASTM D6866 was developed in the United States as a standardized analytical method for determining the biobased content of solid, liquid, and gaseous samples using radiocarbon dating by the American Society for Testing and Materials (ASTM) International. The standard is based on the use of radiocarbon dating for the determination of a product's biobased content. ASTM D6866 was first published in 2004, and the current active version of the standard is ASTM D6866-11 (effective Apr. 1, 2011). Radiocarbon dating techniques are well known to those skilled in the art, including those described herein.
The biobased content of a compound is estimated by the ratio of carbon-14 (¹⁴C) to carbon-12 (¹²C). Specifically, the Fraction Modern (Fm) is computed from the expression: Fm=(S−B)/(M−B), where B, S and M represent the ¹⁴C/¹²C ratios of the blank, the sample and the modern reference, respectively. Fraction Modern is a measurement of the deviation of the ¹⁴C/¹²C ratio of a sample from “Modern.” Modern is defined as 95% of the radiocarbon concentration (in AD 1950) of National Bureau of Standards (NBS) Oxalic Acid I (i.e., standard reference materials (SRM) 4990b) normalized to δ¹³C_VPDB=−19 per mil (Olsson, The use of Oxalic acid as a Standard. in, Radiocarbon Variations and Absolute Chronology, Nobel Symposium, 12th Proc., John Wiley & Sons, New York (1970)). Mass spectrometry results, for example, measured by ASM, are calculated using the internationally agreed upon definition of 0.95 times the specific activity of NBS Oxalic Acid I (SRM 4990b) normalized to δ¹³C_VPDB=−19 per mil. This is equivalent to an absolute (AD 1950)¹⁴C/¹²C ratio of 1.176±0.010×10⁻¹²(Karlen et al., Arkiv Geofysik, 4:465-471 (1968)). The standard calculations take into account the differential uptake of one istope with respect to another, for example, the preferential uptake in biological systems of C¹²over C¹³over C¹⁴, and these corrections are reflected as a Fm corrected for δ¹³.
An oxalic acid standard (SRM 4990b or HOx 1) was made from a crop of 1955 sugar beet. Although there were 1000 lbs made, this oxalic acid standard is no longer commercially available. The Oxalic Acid II standard (HOx 2; N.I.S.T designation SRM 4990 C) was made from a crop of 1977 French beet molasses. In the early 1980's, a group of 12 laboratories measured the ratios of the two standards. The ratio of the activity of Oxalic acid II to 1 is 1.2933±0.001 (the weighted mean). The isotopic ratio of HOx II is −17.8 per mille. ASTM D6866-11 suggests use of the available Oxalic Acid II standard SRM 4990 C (Hox2) for the modern standard (see discussion of original vs. currently available oxalic acid standards in Mann, Radiocarbon, 25(2):519-527 (1983)). A Fm=0% represents the entire lack of carbon-14 atoms in a material, thus indicating a fossil (for example, petroleum based) carbon source. A Fm=100%, after correction for the post-1950 injection of carbon-14 into the atmosphere from nuclear bomb testing, indicates an entirely modern carbon source. As described herein, such a “modern” source includes biobased sources.
As described in ASTM D6866, the percent modern carbon (pMC) can be greater than 100% because of the continuing but diminishing effects of the 1950s nuclear testing programs, which resulted in a considerable enrichment of carbon-14 in the atmosphere as described in ASTM D6866-11. Because all sample carbon-14 activities are referenced to a “pre-bomb” standard, and because nearly all new biobased products are produced in a post-bomb environment, all pMC values (after correction for isotopic fraction) must be multiplied by 0.95 (as of 2010) to better reflect the true biobased content of the sample. A biobased content that is greater than 103% suggests that either an analytical error has occurred, or that the source of biobased carbon is more than several years old.
ASTM D6866 quantifies the biobased content relative to the material's total organic content and does not consider the inorganic carbon and other non-carbon containing substances present. For example, a product that is 50% starch-based material and 50% water would be considered to have a Biobased Content=100% (50% organic content that is 100% biobased) based on ASTM D6866. In another example, a product that is 50% starch-based material, 25% petroleum-based, and 25% water would have a Biobased Content=66.7% (75% organic content but only 50% of the product is biobased). In another example, a product that is 50% organic carbon and is a petroleum-based product would be considered to have a Biobased Content=0% (50% organic carbon but from fossil sources). Thus, based on the well known methods and known standards for determining the biobased content of a compound or material, one skilled in the art can readily determine the biobased content and/or prepared downstream products that utilize of the invention having a desired biobased content.
Applications of carbon-14 dating techniques to quantify bio-based content of materials are known in the art (Currie et al., Nuclear Instruments and Methods in Physics Research B, 172:281-287 (2000)). For example, carbon-14 dating has been used to quantify bio-based content in terephthalate-containing materials (Colonna et al., Green Chemistry, 13:2543-2548 (2011)). Notably, polypropylene terephthalate (PPT) polymers derived from renewable 1,3-propanediol and petroleum-derived terephthalic acid resulted in Fm values near 30% (i.e., since 3/11 of the polymeric carbon derives from renewable 1,3-propanediol and 8/11 from the fossil end member terephthalic acid) (Currie et al., supra, 2000). In contrast, polybutylene terephthalate polymer derived from both renewable 1,4-butanediol and renewable terephthalic acid resulted in bio-based content exceeding 90% (Colonna et al., supra, 2011).
Accordingly, in some embodiments, the present invention provides caprolactone or a caprolactone pathway intermediate that has a carbon-12, carbon-13, and carbon-14 ratio that reflects an atmospheric carbon, also referred to as environmental carbon, uptake source. For example, in some aspects the caprolactone or a caprolactone pathway intermediate can have an Fm value of at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 98% or as much as 100%. In some such embodiments, the uptake source is CO₂. In some embodiments, the present invention provides caprolactone or a caprolactone pathway intermediate that has a carbon-12, carbon-13, and carbon-14 ratio that reflects petroleum-based carbon uptake source. In this aspect, the caprolactone or a caprolactone pathway intermediate can have an Fm value of less than 95%, less than 90%, less than 85%, less than 80%, less than 75%, less than 70%, less than 65%, less than 60%, less than 55%, less than 50%, less than 45%, less than 40%, less than 35%, less than 30%, less than 25%, less than 20%, less than 15%, less than 10%, less than 5%, less than 2% or less than 1%. In some embodiments, the present invention provides caprolactone or a caprolactone pathway intermediate that has a carbon-12, carbon-13, and carbon-14 ratio that is obtained by a combination of an atmospheric carbon uptake source with a petroleum-based uptake source. Using such a combination of uptake sources is one way by which the carbon-12, carbon-13, and carbon-14 ratio can be varied, and the respective ratios would reflect the proportions of the uptake sources.
Further, the present invention relates to the biologically produced caprolactone or caprolactone pathway intermediate as disclosed herein, and to the products derived therefrom, wherein the caprolactone or a caprolactone pathway intermediate has a carbon-12, carbon-13, and carbon-14 isotope ratio of about the same value as the CO₂that occurs in the environment. For example, in some aspects the invention provides bioderived caprolactone or a bioderived caprolactone intermediate having a carbon-12 versus carbon-13 versus carbon-14 isotope ratio of about the same value as the CO₂that occurs in the environment, or any of the other ratios disclosed herein. It is understood, as disclosed herein, that a product can have a carbon-12 versus carbon-13 versus carbon-14 isotope ratio of about the same value as the CO₂that occurs in the environment, or any of the ratios disclosed herein, wherein the product is generated from bioderived caprolactone or a bioderived caprolactone pathway intermediate as disclosed herein, wherein the bioderived product is chemically modified to generate a final product. Methods of chemically modifying a bioderived product of caprolactone, or an intermediate thereof, to generate a desired product are well known to those skilled in the art, as described herein. The invention further provides a polymer, a resin, a protective or industrial coating, polyurethane, a cast elastomer, an adhesive, a colorant, or a pharmaceutical having a carbon-12 versus carbon-13 versus carbon-14 isotope ratio of about the same value as the CO₂that occurs in the environment, wherein the polymer, resin, protective or industrial coating, polyurethane, cast elastomer, adhesive, colorant, or pharmaceutical is generated directly from or in combination with bioderived caprolactone or a bioderived caprolactone pathway intermediate as disclosed herein.
Caprolactone is a chemical used in commercial and industrial applications. Non-limiting examples of such applications include production of a polymer, a resin, a protective or industrial coating, polyurethane, a cast elastomer, an adhesive, a colorant, or a pharmaceutical. Accordingly, in some embodiments, the invention provides a biobased polymer, resin, protective or industrial coating, polyurethane, cast elastomer, adhesive, colorant, or pharmaceutical comprising one or more bioderived caprolactone or bioderived caprolactone pathway intermediate produced by a non-naturally occurring microorganism of the invention or produced using a method disclosed herein.
As used herein, the term “bioderived” means derived from or synthesized by a biological organism and can be considered a renewable resource since it can be generated by a biological organism. Such a biological organism, in particular the microbial organisms of the invention disclosed herein, can utilize feedstock or biomass, such as, sugars or carbohydrates obtained from an agricultural, plant, bacterial, or animal source. Alternatively, the biological organism can utilize atmospheric carbon. As used herein, the term “biobased” means a product as described above that is composed, in whole or in part, of a bioderived compound of the invention. A biobased or bioderived product is in contrast to a petroleum derived product, wherein such a product is derived from or synthesized from petroleum or a petrochemical feedstock.
In some embodiments, the invention provides a polymer, a resin, a protective or industrial coating, polyurethane, a cast elastomer, an adhesive, a colorant, or a pharmaceutical comprising bioderived caprolactone or bioderived caprolactone pathway intermediate, wherein the bioderived caprolactone or bioderived caprolactone pathway intermediate includes all or part of the caprolactone or caprolactone pathway intermediate used in the production of the polymer, resin, protective or industrial coating, polyurethane, cast elastomer, adhesive, colorant, or pharmaceutical. For example, the final polymer, resin, protective or industrial coating, polyurethane, cast elastomer, adhesive, colorant, or pharmaceutical can contain the bioderived caprolactone, caprolactone pathway intermediate, or a portion thereof that is the result of the manufacturing of polymer, resin, protective or industrial coating, polyurethane, cast elastomer, adhesive, colorant, or pharmaceutical. Such manufacturing can include chemically reacting the bioderived caprolactone or bioderived caprolactone pathway intermediate (e.g. chemical conversion, chemical functionalization, chemical coupling, oxidation, reduction, polymerization, copolymerization and the like) into the final polymer, protective or industrial coating, polyurethane, cast elastomer, adhesive, colorant, or pharmaceutical. For example, a portion of bioderived caprolactone can be a repeating unit in the polymer, resin, protective or industrial coating, polyurethane, cast elastomer, adhesive, colorant, or pharmaceutical. Thus, in some aspects, the invention provides a composition including for example, a biobased polymer, resin, protective or industrial coating, polyurethane, cast elastomer, adhesive, colorant, or pharmaceutical comprising at least 1%, at least 2%, at least 3%, at least 4%, at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 98% or 100% (w/v) bioderived caprolactone or bioderived caprolactone pathway intermediate as disclosed herein. In some aspects, the invention provides a process for producing a biobased polymer or resin disclosed herein by chemically reacting the bioderived caprolactone with itself or another compound in a polymer producing or a resin producting reaction. It is understood that such process are well known in the art.
Additionally, in some embodiments, the invention provides a composition having a bioderived caprolactone or caprolactone pathway intermediate disclosed herein and a compound other than the bioderived caprolactone or caprolactone pathway intermediate. For example, in some aspects, the invention provides a biobased polymer, resin, protective or industrial coating, polyurethane, cast elastomer, adhesive, colorant, or pharmaceutical wherein the caprolactone or caprolactone pathway intermediate used in its production is a combination of bioderived and petroleum derived caprolactone or caprolactone pathway intermediate. For example, a biobased polymer, resin, protective or industrial coating, polyurethane, cast elastomer, adhesive, colorant, or pharmaceutical can be produced using 50% bioderived caprolactone and 50% petroleum derived caprolactone or other desired ratios such as 60%/40%, 70%/30%, 80%/20%, 90%/10%, 95%/5%, 100%/0%, 40%/60%, 30%/70%, 20%/80%, 10%/90% of bioderived/petroleum derived precursors, so long as at least a portion of the product comprises a bioderived product produced by the microbial organisms disclosed herein. It is understood that methods for producing a polymer, resin, a protective or industrial coating, polyurethane, a cast elastomer, an adhesive, a colorant, or a pharmaceutical using the bioderived caprolactone or bioderived caprolactone pathway intermediate of the invention are well known in the art.
In another aspect, the compound other than the bioderived caprolactone in a composition of the invention is a trace amount of a cellular portion of a non-naturally occurring microbial organism having a caprolactone pathway of the invention disclosed here. A cellular portion of a microbial organism includes without limitation proteins, polypeptides, peptides, amino acids, nucleic acids, polynucleotides, components of the cell wall or a cellular membrane including, for example, peptidoglycans, glycoproteins, and polysaccharides, or any other cellular component. A “trace amount” as used herein refers to the presence of a compound or material in the composition, but in a quantity approaching a detectable limit. Such trace amounts can be so small as to not be accurately measured.
In some embodiments, the invention provides a molded product obtained by molding a biobased polymer or resin disclosed herein. Such moled products may be produced in to any number of industrially desireable forms including for example, a pellet.
The culture conditions can include, for example, liquid culture procedures as well as fermentation and other large scale culture procedures. As described herein, particularly useful yields of the biosynthetic products of the invention can be obtained under anaerobic or substantially anaerobic culture conditions.
As described herein, one exemplary growth condition for achieving biosynthesis of caprolactone includes anaerobic culture or fermentation conditions. In certain embodiments, the non-naturally occurring microbial organisms of the invention can be sustained, cultured or fermented under anaerobic or substantially anaerobic conditions. Briefly, an anaerobic condition refers to an environment devoid of oxygen. Substantially anaerobic conditions include, for example, a culture, batch fermentation or continuous fermentation such that the dissolved oxygen concentration in the medium remains between 0 and 10% of saturation. Substantially anaerobic conditions also includes growing or resting cells in liquid medium or on solid agar inside a sealed chamber maintained with an atmosphere of less than 1% oxygen. The percent of oxygen can be maintained by, for example, sparging the culture with an N₂/CO₂mixture or other suitable non-oxygen gas or gases.
The culture conditions described herein can be scaled up and grown continuously for manufacturing of caprolactone. Exemplary growth procedures include, for example, fed-batch fermentation and batch separation; fed-batch fermentation and continuous separation, or continuous fermentation and continuous separation. All of these processes are well known in the art. Fermentation procedures are particularly useful for the biosynthetic production of commercial quantities of caprolactone. Generally, and as with non-continuous culture procedures, the continuous and/or near-continuous production of caprolactone will include culturing a non-naturally occurring caprolactone producing organism of the invention in sufficient nutrients and medium to sustain and/or nearly sustain growth in an exponential phase. Continuous culture under such conditions can include, for example, growth for 1 day, 2, 3, 4, 5, 6 or 7 days or more. Additionally, continuous culture can include longer time periods of 1 week, 2, 3, 4 or 5 or more weeks and up to several months. Alternatively, organisms of the invention can be cultured for hours, if suitable for a particular application. It is to be understood that the continuous and/or near-continuous culture conditions also can include all time intervals in between these exemplary periods. It is further understood that the time of culturing the microbial organism of the invention is for a sufficient period of time to produce a sufficient amount of product for a desired purpose.
Fermentation procedures are well known in the art. Briefly, fermentation for the biosynthetic production of caprolactone can be utilized in, for example, fed-batch fermentation and batch separation; fed-batch fermentation and continuous separation, or continuous fermentation and continuous separation. Examples of batch and continuous fermentation procedures are well known in the art.
In addition to the above fermentation procedures using the caprolactone producers of the invention for continuous production of substantial quantities of caprolactone, the caprolactone producers also can be, for example, simultaneously subjected to chemical synthesis procedures to convert the product to other compounds or the product can be separated from the fermentation culture and sequentially subjected to chemical or enzymatic conversion to convert the product to other compounds, if desired.
To generate better producers, metabolic modeling can be utilized to optimize growth conditions. Modeling can also be used to design gene knockouts that additionally optimize utilization of the pathway (see, for example, U.S. patent publications US 2002/0012939, US 2003/0224363, US 2004/0029149, US 2004/0072723, US 2003/0059792, US 2002/0168654 and US 2004/0009466, and U.S. Pat. No. 7,127,379). Modeling analysis allows reliable predictions of the effects on cell growth of shifting the metabolism towards more efficient production of caprolactone.
One computational method for identifying and designing metabolic alterations favoring biosynthesis of a desired product is the OptKnock computational framework (Burgard et al., Biotechnol. Bioeng. 84:647-657 (2003)). OptKnock is a metabolic modeling and simulation program that suggests gene deletion or disruption strategies that result in genetically stable microorganisms which overproduce the target product. Specifically, the framework examines the complete metabolic and/or biochemical network of a microorganism in order to suggest genetic manipulations that force the desired biochemical to become an obligatory byproduct of cell growth. By coupling biochemical production with cell growth through strategically placed gene deletions or other functional gene disruption, the growth selection pressures imposed on the engineered strains after long periods of time in a bioreactor lead to improvements in performance as a result of the compulsory growth-coupled biochemical production. Lastly, when gene deletions are constructed there is a negligible possibility of the designed strains reverting to their wild-type states because the genes selected by OptKnock are to be completely removed from the genome. Therefore, this computational methodology can be used to either identify alternative pathways that lead to biosynthesis of a desired product or used in connection with the non-naturally occurring microbial organisms for further optimization of biosynthesis of a desired product.
Briefly, OptKnock is a term used herein to refer to a computational method and system for modeling cellular metabolism. The OptKnock program relates to a framework of models and methods that incorporate particular constraints into flux balance analysis (FBA) models. These constraints include, for example, qualitative kinetic information, qualitative regulatory information, and/or DNA microarray experimental data. OptKnock also computes solutions to various metabolic problems by, for example, tightening the flux boundaries derived through flux balance models and subsequently probing the performance limits of metabolic networks in the presence of gene additions or deletions. OptKnock computational framework allows the construction of model formulations that allow an effective query of the performance limits of metabolic networks and provides methods for solving the resulting mixed-integer linear programming problems. The metabolic modeling and simulation methods referred to herein as OptKnock are described in, for example, U.S. publication 2002/0168654, filed Jan. 10, 2002, in International Patent No. PCT/US02/00660, filed Jan. 10, 2002, and U.S. publication 2009/0047719, filed Aug. 10, 2007.
Another computational method for identifying and designing metabolic alterations favoring biosynthetic production of a product is a metabolic modeling and simulation system termed SimPheny®. This computational method and system is described in, for example, U.S. publication 2003/0233218, filed Jun. 14, 2002, and in International Patent Application No. PCT/US03/18838, filed Jun. 13, 2003. SimPheny® is a computational system that can be used to produce a network model in silico and to simulate the flux of mass, energy or charge through the chemical reactions of a biological system to define a solution space that contains any and all possible functionalities of the chemical reactions in the system, thereby determining a range of allowed activities for the biological system. This approach is referred to as constraints-based modeling because the solution space is defined by constraints such as the known stoichiometry of the included reactions as well as reaction thermodynamic and capacity constraints associated with maximum fluxes through reactions. The space defined by these constraints can be interrogated to determine the phenotypic capabilities and behavior of the biological system or of its biochemical components.
These computational approaches are consistent with biological realities because biological systems are flexible and can reach the same result in many different ways. Biological systems are designed through evolutionary mechanisms that have been restricted by fundamental constraints that all living systems must face. Therefore, constraints-based modeling strategy embraces these general realities. Further, the ability to continuously impose further restrictions on a network model via the tightening of constraints results in a reduction in the size of the solution space, thereby enhancing the precision with which physiological performance or phenotype can be predicted.
Given the teachings and guidance provided herein, those skilled in the art will be able to apply various computational frameworks for metabolic modeling and simulation to design and implement biosynthesis of a desired compound in host microbial organisms. Such metabolic modeling and simulation methods include, for example, the computational systems exemplified above as SimPheny® and OptKnock. For illustration of the invention, some methods are described herein with reference to the OptKnock computation framework for modeling and simulation. Those skilled in the art will know how to apply the identification, design and implementation of the metabolic alterations using OptKnock to any of such other metabolic modeling and simulation computational frameworks and methods well known in the art.
The methods described above will provide one set of metabolic reactions to disrupt. Elimination of each reaction within the set or metabolic modification can result in a desired product as an obligatory product during the growth phase of the organism. Because the reactions are known, a solution to the bilevel OptKnock problem also will provide the associated gene or genes encoding one or more enzymes that catalyze each reaction within the set of reactions. Identification of a set of reactions and their corresponding genes encoding the enzymes participating in each reaction is generally an automated process, accomplished through correlation of the reactions with a reaction database having a relationship between enzymes and encoding genes.
Once identified, the set of reactions that are to be disrupted in order to achieve production of a desired product are implemented in the target cell or organism by functional disruption of at least one gene encoding each metabolic reaction within the set. One particularly useful means to achieve functional disruption of the reaction set is by deletion of each encoding gene. However, in some instances, it can be beneficial to disrupt the reaction by other genetic aberrations including, for example, mutation, deletion of regulatory regions such as promoters or cis binding sites for regulatory factors, or by truncation of the coding sequence at any of a number of locations. These latter aberrations, resulting in less than total deletion of the gene set can be useful, for example, when rapid assessments of the coupling of a product are desired or when genetic reversion is less likely to occur.
To identify additional productive solutions to the above described bilevel OptKnock problem which lead to further sets of reactions to disrupt or metabolic modifications that can result in the biosynthesis, including growth-coupled biosynthesis of a desired product, an optimization method, termed integer cuts, can be implemented. This method proceeds by iteratively solving the OptKnock problem exemplified above with the incorporation of an additional constraint referred to as an integer cut at each iteration. Integer cut constraints effectively prevent the solution procedure from choosing the exact same set of reactions identified in any previous iteration that obligatorily couples product biosynthesis to growth. For example, if a previously identified growth-coupled metabolic modification specifies reactions 1, 2, and 3 for disruption, then the following constraint prevents the same reactions from being simultaneously considered in subsequent solutions. The integer cut method is well known in the art and can be found described in, for example, Burgard et al., Biotechnol. Prog. 17:791-797 (2001). As with all methods described herein with reference to their use in combination with the OptKnock computational framework for metabolic modeling and simulation, the integer cut method of reducing redundancy in iterative computational analysis also can be applied with other computational frameworks well known in the art including, for example, SimPheny®.
The methods exemplified herein allow the construction of cells and organisms that biosynthetically produce a desired product, including the obligatory coupling of production of a target biochemical product to growth of the cell or organism engineered to harbor the identified genetic alterations. Therefore, the computational methods described herein allow the identification and implementation of metabolic modifications that are identified by an in silico method selected from OptKnock or SimPheny®. The set of metabolic modifications can include, for example, addition of one or more biosynthetic pathway enzymes and/or functional disruption of one or more metabolic reactions including, for example, disruption by gene deletion.
As discussed above, the OptKnock methodology was developed on the premise that mutant microbial networks can be evolved towards their computationally predicted maximum-growth phenotypes when subjected to long periods of growth selection. In other words, the approach leverages an organism's ability to self-optimize under selective pressures. The OptKnock framework allows for the exhaustive enumeration of gene deletion combinations that force a coupling between biochemical production and cell growth based on network stoichiometry. The identification of optimal gene/reaction knockouts requires the solution of a bilevel optimization problem that chooses the set of active reactions such that an optimal growth solution for the resulting network overproduces the biochemical of interest (Burgard et al., Biotechnol. Bioeng. 84:647-657 (2003)).
An in silico stoichiometric model of E. coli metabolism can be employed to identify essential genes for metabolic pathways as exemplified previously and described in, for example, U.S. patent publications US 2002/0012939, US 2003/0224363, US 2004/0029149, US 2004/0072723, US 2003/0059792, US 2002/0168654 and US 2004/0009466, and in U.S. Pat. No. 7,127,379. As disclosed herein, the OptKnock mathematical framework can be applied to pinpoint gene deletions leading to the growth-coupled production of a desired product. Further, the solution of the bilevel OptKnock problem provides only one set of deletions. To enumerate all meaningful solutions, that is, all sets of knockouts leading to growth-coupled production formation, an optimization technique, termed integer cuts, can be implemented. This entails iteratively solving the OptKnock problem with the incorporation of an additional constraint referred to as an integer cut at each iteration, as discussed above.
As disclosed herein, a nucleic acid encoding a desired activity of a caprolactone pathway can be introduced into a host organism. In some cases, it can be desirable to modify an activity of a caprolactone pathway enzyme or protein to increase production of caprolactone. For example, known mutations that increase the activity of a protein or enzyme can be introduced into an encoding nucleic acid molecule. Additionally, optimization methods can be applied to increase the activity of an enzyme or protein and/or decrease an inhibitory activity, for example, decrease the activity of a negative regulator.
One such optimization method is directed evolution. Directed evolution is a powerful approach that involves the introduction of mutations targeted to a specific gene in order to improve and/or alter the properties of an enzyme. Improved and/or altered enzymes can be identified through the development and implementation of sensitive high-throughput screening assays that allow the automated screening of many enzyme variants (for example, >10⁴). Iterative rounds of mutagenesis and screening typically are performed to afford an enzyme with optimized properties. Computational algorithms that can help to identify areas of the gene for mutagenesis also have been developed and can significantly reduce the number of enzyme variants that need to be generated and screened. Numerous directed evolution technologies have been developed (for reviews, see Hibbert et al., Biomol. Eng 22:11-19 (2005); Huisman and Lalonde, In Biocatalysis in the pharmaceutical and biotechnology industries pgs. 717-742 (2007), Patel (ed.), CRC Press; Otten and Quax. Biomol. Eng 22:1-9 (2005).; and Sen et al., Appl Biochem. Biotechnol 143:212-223 (2007)) to be effective at creating diverse variant libraries, and these methods have been successfully applied to the improvement of a wide range of properties across many enzyme classes. Enzyme characteristics that have been improved and/or altered by directed evolution technologies include, for example: selectivity/specificity, for conversion of non-natural substrates; temperature stability, for robust high temperature processing; pH stability, for bioprocessing under lower or higher pH conditions; substrate or product tolerance, so that high product titers can be achieved; binding (K_m), including broadening substrate binding to include non-natural substrates; inhibition (K_i), to remove inhibition by products, substrates, or key intermediates; activity (kcat), to increases enzymatic reaction rates to achieve desired flux; expression levels, to increase protein yields and overall pathway flux; oxygen stability, for operation of air sensitive enzymes under aerobic conditions; and anaerobic activity, for operation of an aerobic enzyme in the absence of oxygen.
A number of exemplary methods have been developed for the mutagenesis and diversification of genes to target desired properties of specific enzymes. Such methods are well known to those skilled in the art. Any of these can be used to alter and/or optimize the activity of a caprolactone pathway enzyme or protein. Such methods include, but are not limited to EpPCR, which introduces random point mutations by reducing the fidelity of DNA polymerase in PCR reactions (Pritchard et al., J Theor. Biol. 234:497-509 (2005)); Error-prone Rolling Circle Amplification (epRCA), which is similar to epPCR except a whole circular plasmid is used as the template and random 6-mers with exonuclease resistant thiophosphate linkages on the last 2 nucleotides are used to amplify the plasmid followed by transformation into cells in which the plasmid is re-circularized at tandem repeats (Fujii et al., Nucleic Acids Res. 32:e145 (2004); and Fujii et al., Nat. Protoc. 1:2493-2497 (2006)); DNA or Family Shuffling, which typically involves digestion of two or more variant genes with nucleases such as Dnase I or EndoV to generate a pool of random fragments that are reassembled by cycles of annealing and extension in the presence of DNA polymerase to create a library of chimeric genes (Stemmer, Proc Natl Acad Sci USA 91:10747-10751 (1994); and Stemmer, Nature 370:389-391 (1994)); Staggered Extension (StEP), which entails template priming followed by repeated cycles of 2 step PCR with denaturation and very short duration of annealing/extension (as short as 5 sec) (Zhao et al., Nat. Biotechnol. 16:258-261 (1998)); Random Priming Recombination (RPR), in which random sequence primers are used to generate many short DNA fragments complementary to different segments of the template (Shao et al., Nucleic Acids Res 26:681-683 (1998)).
Additional methods include Heteroduplex Recombination, in which linearized plasmid DNA is used to form heteroduplexes that are repaired by mismatch repair (Volkov et al, Nucleic Acids Res. 27:e18 (1999); and Volkov et al., Methods Enzymol. 328:456-463 (2000)); Random Chimeragenesis on Transient Templates (RACHITT), which employs Dnase I fragmentation and size fractionation of single stranded DNA (ssDNA) (Coco et al., Nat. Biotechnol. 19:354-359 (2001)); Recombined Extension on Truncated templates (RETT), which entails template switching of unidirectionally growing strands from primers in the presence of unidirectional ssDNA fragments used as a pool of templates (Lee et al., J. Molec. Catalysis 26:119-129 (2003)); Degenerate Oligonucleotide Gene Shuffling (DOGS), in which degenerate primers are used to control recombination between molecules; (Bergquist and Gibbs, Methods Mol. Biol 352:191-204 (2007); Bergquist et al., Biomol. Eng 22:63-72 (2005); Gibbs et al., Gene 271:13-20 (2001)); Incremental Truncation for the Creation of Hybrid Enzymes (ITCHY), which creates a combinatorial library with 1 base pair deletions of a gene or gene fragment of interest (Ostermeier et al., Proc. Natl. Acad. Sci. USA 96:3562-3567 (1999); and Ostermeier et al., Nat. Biotechnol. 17:1205-1209 (1999)); Thio-Incremental Truncation for the Creation of Hybrid Enzymes (THIO-ITCHY), which is similar to ITCHY except that phosphothioate dNTPs are used to generate truncations (Lutz et al., Nucleic Acids Res 29:E16 (2001)); SCRATCHY, which combines two methods for recombining genes, ITCHY and DNA shuffling (Lutz et al., Proc. Natl. Acad. Sci. USA 98:11248-11253 (2001)); Random Drift Mutagenesis (RNDM), in which mutations made via epPCR are followed by screening/selection for those retaining usable activity (Bergquist et al., Biomol. Eng. 22:63-72 (2005)); Sequence Saturation Mutagenesis (SeSaM), a random mutagenesis method that generates a pool of random length fragments using random incorporation of a phosphothioate nucleotide and cleavage, which is used as a template to extend in the presence of “universal” bases such as inosine, and replication of an inosine-containing complement gives random base incorporation and, consequently, mutagenesis (Wong et al., Biotechnol. J. 3:74-82 (2008); Wong et al., Nucleic Acids Res. 32:e26 (2004); and Wong et al., Anal. Biochem. 341:187-189 (2005)); Synthetic Shuffling, which uses overlapping oligonucleotides designed to encode “all genetic diversity in targets” and allows a very high diversity for the shuffled progeny (Ness et al., Nat. Biotechnol. 20:1251-1255 (2002)); Nucleotide Exchange and Excision Technology NexT, which exploits a combination of dUTP incorporation followed by treatment with uracil DNA glycosylase and then piperidine to perform endpoint DNA fragmentation (Muller et al., Nucleic Acids Res. 33:e117 (2005)).
Further methods include Sequence Homology-Independent Protein Recombination (SHIPREC), in which a linker is used to facilitate fusion between two distantly related or unrelated genes, and a range of chimeras is generated between the two genes, resulting in libraries of single-crossover hybrids (Sieber et al., Nat. Biotechnol. 19:456-460 (2001)); Gene Site Saturation Mutagenesis™ (GSSM™), in which the starting materials include a supercoiled double stranded DNA (dsDNA) plasmid containing an insert and two primers which are degenerate at the desired site of mutations (Kretz et al., Methods Enzymol. 388:3-11 (2004)); Combinatorial Cassette Mutagenesis (CCM), which involves the use of short oligonucleotide cassettes to replace limited regions with a large number of possible amino acid sequence alterations (Reidhaar-Olson et al. Methods Enzymol. 208:564-586 (1991); and Reidhaar-Olson et al. Science 241:53-57 (1988)); Combinatorial Multiple Cassette Mutagenesis (CMCM), which is essentially similar to CCM and uses epPCR at high mutation rate to identify hot spots and hot regions and then extension by CMCM to cover a defined region of protein sequence space (Reetz et al., Angew. Chem. Int. EdEngl. 40:3589-3591 (2001)); the Mutator Strains technique, in which conditional ts mutator plasmids, utilizing the mutD5 gene, which encodes a mutant subunit of DNA polymerase III, to allow increases of 20 to 4000-× in random and natural mutation frequency during selection and block accumulation of deleterious mutations when selection is not required (Selifonova et al., Appl. Environ. Microbiol. 67:3645-3649 (2001)); Low et al., J. Mol. Biol. 260:359-3680 (1996)).
Additional exemplary methods include Look-Through Mutagenesis (LTM), which is a multidimensional mutagenesis method that assesses and optimizes combinatorial mutations of selected amino acids (Rajpal et al., Proc. Natl. Acad. Sci. USA 102:8466-8471 (2005)); Gene Reassembly, which is a DNA shuffling method that can be applied to multiple genes at one time or to create a large library of chimeras (multiple mutations) of a single gene (Tunable GeneReassembly™ (TGR™) Technology supplied by Verenium Corporation), in Silico Protein Design Automation (PDA), which is an optimization algorithm that anchors the structurally defined protein backbone possessing a particular fold, and searches sequence space for amino acid substitutions that can stabilize the fold and overall protein energetics, and generally works most effectively on proteins with known three-dimensional structures (Hayes et al., Proc. Natl. Acad. Sci. USA 99:15926-15931 (2002)); and Iterative Saturation Mutagenesis (ISM), which involves using knowledge of structure/function to choose a likely site for enzyme improvement, performing saturation mutagenesis at chosen site using a mutagenesis method such as Stratagene QuikChange (Stratagene; San Diego Calif.), screening/selecting for desired properties, and, using improved clone(s), starting over at another site and continue repeating until a desired activity is achieved (Reetz et al., Nat. Protoc. 2:891-903 (2007); and Reetz et al., Angew. Chem. Int. EdEngl. 45:7745-7751 (2006)).
Any of the aforementioned methods for mutagenesis can be used alone or in any combination. Additionally, any one or combination of the directed evolution methods can be used in conjunction with adaptive evolution techniques, as described herein.
It is understood that modifications which do not substantially affect the activity of the various embodiments of this invention are also provided within the definition of the invention provided herein. Accordingly, the following examples are intended to illustrate but not limit the present invention.

Example I

Production of Caprolactone

Several pathways for producing caprolactone are depicted in FIGS. 1-5. Each pathway originates from naturally occurring metabolites. FIG. 1 shows pathways for converting adipate or adipyl-CoA to caprolactone. Adipate is an intermediate produced during the degradation of aromatic and aliphatic ring containing compounds such as cyclohexanol. Biosynthetic pathways for forming adipate and adipyl-CoA are well known in the art (for example, see U.S. Pat. No. 7,799,545). In the pathway shown in FIG. 1, adipate semialdehyde is formed either from adipate via an adipate reductase (Step E) or adipyl-CoA via adipyl-CoA reductase (Step A). Adipate semialdehyde is then reduced to 5-hydroxyhexanoate in Step B. The 6-hydroxyhexanoate intermediate is converted to caprolactone by one of several alternate routes. In one route, 6-hydroxyhexanoate is directly converted to caprolactone by a caprolactone hydrolase (step G). In yet another route, 6-hydroxyhexanoate is activated to its corresponding acyl-CoA, which then cyclizes to caprolactone (step C/D), or cyclizes via a 6-hydroxyhexanoyl-phosphate intermediate (steps J/I). In an alternate route, 6-hydroxyhexanote is activated to 6-hydroxyhexanoyl-phoshphate, which is then cyclized to caprolactone (step H/I).
A similar series of pathways is shown in FIG. 2. These pathways originate from 4-hydroxybutyryl-CoA, an intermediate in the biosynthesis of poly-hydroxyalkanoates and non-naturally occurring chemicals such as 1,4-butanediol (see U.S. Pat. Nos. 7,947,483, 7,229,804). In the first step of FIG. 2 pathways, 4-hydroxybutyryl-CoA and acetyl-CoA are joined by a beta-ketothiolase to form 3-oxo-6-hydroxyhexanoyl-CoA. This intermediate is reduced and dehydrated to 6-hydroxyhex-2-enoyl-CoA (steps B/C). Reduction of 6-hydroxyhex-2-enoyl-CoA yields 6-hydroxyhexanoyl-CoA in Step D. 6-Hydroxyhexanoyl-CoA is directly converted to caprolactone either spontaneously or by an enzyme (step G). Alternately, caprolactone is formed via a phosphate intermediate (steps H/I) and/or 6-hydroxyhexanoate (steps E/J/I or steps E/F).
In another embodiment, the caprolactone is derived from cyclohexanone as shown in FIG. 3. The conversion of cyclohexanone to caprolactone by enzymes with cyclohexanone monooxygenase activity is well known in the art (see for example, U.S. Pat. No. 6,790,645 and U.S. Pat. No. 7,105,296). Exemplary pathways for biosynthesizing cyclohexanone from metabolic intermediates are shown in FIGS. 4 and 5.
FIG. 4 shows a pathway for converting adipate semialdehyde to cyclohexanone in four enzymatic steps. In the first step, adipate semialdehyde is simultaneously dehydrated and cyclized, forming cyclohexane-1,2-dione. Reduction of the two keto groups to alcohol groups is catalyzed by one or more enzymes with cyclohexane-1,2-dione reductase and 2-hydroxycyclohexanone reductase activities. Finally, a diol dehydratase converts cyclohexane-1,2-diol to cyclohexanone.
Cyclohexanone can alternately be synthesized from pimeloyl-CoA as shown in FIG. 5. Pimeloyl-CoA is a naturally occurring intermediate of metabolic pathways including biotin biosynthesis and degradation pathways of aromatic compounds. In the proposed cyclohexanone pathway, pimeloyl-CoA is cyclized to 2-ketocyclohexane-1-carboxyl-CoA by 2-ketocyclohexane-1-carboxyl-CoA hydrolase (acting on C—C). The CoA ester is then converted to 2-ketocyclohexane-1-carboxylate by a CoA synthetase, hydrolase or transferase. Finally decarboxylation of 2-ketocyclohexane-1-carboxylate yields cyclohexanone.

Enzymes


EC class	Description	FIG. 1	FIG. 2	FIG. 3	FIG. 4	FIG. 5

1.1.1.a	Oxidoreductase (oxo to	1B	2B		4B, 4C
	alcohol)
1.14.13.a	Monooxygenase (O₂			3A
	incorporating)
1.2.1.b	Oxidoreductase (acyl-	1A
	CoA to aldehyde)
1.2.1.e	Oxidoreductase (acid to	1E
	aldehyde)
1.3.1.a	Oxidoreductase (alkene		2D
	to alkane)
2.3.1.a	Phosphotransacylase	1J		2H
2.3.1.b	Beta-ketothiolase		2A
2.7.2.a	Kinase	1H	2J
2.8.3.a	CoA transferase	1C, 1F	2E			5B
3.1.1.a	Esterase	1G	2F
3.1.2.a	CoA hydrolase	1F				5B
3.7.1.a	Hydrolase				4D	5A
4.1.1.a	Decarboxylase					5C
4.2.1.a	Hydro-lyase		2C		4A
6.2.1.a	CoA synthetase	1C, 1F	2E			5B
N/A		1D, 1I	2G, 2I

1.1.1.a Alcohol Dehydrogenase

Several reactions shown in FIGS. 1, 2 and 4 are catalyzed by alcohol dehydrogenase enzymes. These reactions include Step B of FIG. 1, Step B of FIG. 2 and Steps B and C of FIG. 4. Exemplary alcohol dehydrogenase enzymes are described in further detail below.
6-Hydroxyhexanoate dehydrogenase (adipate semialdehyde reductase) catalyzes the reduction of adipate semialdehyde to 6-hydroxyhexanoate. Such an enzyme is required in Step B of FIG. 1. Enzymes with this activity are found in organisms that degrade cyclohexanone, and are encoded by chnD of Acinetobacter sp. NCIMB9871 (Iwaki et al, AEM 65:5158-62 (1999)), Rhodococcus sp. Phi2 and Arthrobacter sp. BP2 (Brzostowicz et al, AEM 69:334-42 (2003)).


Gene	GenBank ID	GI Number	Organism

chnD	BAC80217.1	33284997	Acinetobacter sp. NCIMB9871
chnD	AAN37477.1	27657618	Arthrobacter sp. BP2
chnD	AAN37489.1	27657631	Rhodococcus sp. Phi2

Additional aldehyde reductase enzymes are shown in the table below. AlrA encodes a medium-chain alcohol dehydrogenase for C2-C14 compounds (Tani et al., Appl. Environ. Microbiol. 66:5231-5235 (2000)). Other candidates are yqhD and fucO from E. coli (Sulzenbacher et al., 342:489-502 (2004)), and bdh I and bdh II from C. acetobutylicum (Walter et al., 174:7149-7158 (1992)). YqhD catalyzes the reduction of a wide range of aldehydes using NADPH as the cofactor, with a preference for chain lengths longer than C(3) (Sulzenbacher et al., 342:489-502 (2004); Perez et al., J Biol. Chem. 283:7346-7353 (2008)). The adhA gene product from Zymomonas mobilis has been demonstrated to have activity on a number of aldehydes including formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, and acrolein (Kinoshita et al., Appl Microbiol Biotechnol 22:249-254 (1985)). Additional aldehyde reductase candidates are encoded by bdh in C. saccharoperbutylacetonicum and Cbei_1722, Cbei_2181 and Cbei_2421 in C. beijerinckii.


Protein	GenBank ID	GI number	Organism

alrA	BAB12273.1	9967138	Acinetobacter
			sp. strain M-1
ADH2	NP_014032.1	6323961	Saccharomyces
			cerevisiae
yqhD	NP_417484.1	16130909	Escherichia coli
fucO	NP_417279.1	16130706	Escherichia coli
bdh I	NP_349892.1	15896543	Clostridium
			acetobutylicum
bdh II	NP_349891.1	15896542	Clostridium
			acetobutylicum
adhA	YP_162971.1	56552132	Zymomonas mobilis
bdh	BAF45463.1	124221917	Clostridium
			saccharoperbu-
			tylacetonicum
Cbei_1722	YP_001308850	150016596	Clostridium beijerinckii
Cbei_2181	YP_001309304	150017050	Clostridium beijerinckii
Cbei_2421	YP_001309535	150017281	Clostridium beijerinckii

Enzymes exhibiting 4-hydroxybutyrate dehydrogenase activity (EC 1.1.1.61) are also suitable candidates. Such enzymes have been characterized in Ralstonia eutropha (Bravo et al., J Forens Sci, 49:379-387 (2004)), Clostridium kluyveri (Wolff et al., Protein Expr. Purif 6:206-212 (1995)) and Arabidopsis thaliana (Breitkreuz et al., J Biol Chem, 278:41552-41556 (2003)). The A. thaliana enzyme was cloned and characterized in yeast. This enzyme also catalyzes the reduction of glutarate semialdehyde to 5-hydroxyvalerate (WO 2010/068953A2). Yet another gene is the alcohol dehydrogenase adhI from Geobacillus thermoglucosidasius (Jeon et al., J Biotechnol 135:127-133 (2008)). An enzyme with similar activity is the glutarate semialdehyde reductase enzyme of Aspergillus terreus, encoded by ATEG_00539 (WO 2010/068953A2).


Protein	GenBank ID	GI number	Organism

4hbd	YP_726053.1	113867564	Ralstonia eutropha
			H16
4hbd	L21902.1	146348486	Clostridium kluyveri
			DSM 555
4hbd	Q94B07	75249805	Arabidopsis thaliana
adhI	AAR91477.1	40795502	Geobacillus
			thermoglucosidasius
ATEG_00539	XP_001210625.1	115491995	Aspergillus terreus
			NIH2624

Aldehyde reductase gene candidates in Saccharomyces cerevisiae include the aldehyde reductases GRE3, ALD2-6 and HFD1, glyoxylate reductases GOR1 and YPL113C and glycerol dehydrogenase GCY1 (WO 2011/022651A1; Atsumi et al., Nature 451:86-89 (2008)). The enzyme candidates described previously for catalyzing the reduction of methylglyoxal to acetol or lactaldehyde are also suitable lactaldehyde reductase enzyme candidates.


Protein	GenBank ID	GI Number	Organism

GRE3	P38715.1	731691	Saccharomyces cerevisiae
ALD2	CAA89806.1	825575	Saccharomyces cerevisiae
ALD3	NP_013892.1	6323821	Saccharomyces cerevisiae
ALD4	NP_015019.1	6324950	Saccharomyces cerevisiae
ALD5	NP_010996.2	330443526	Saccharomyces cerevisiae
ALD6	ABX39192.1	160415767	Saccharomyces cerevisiae
HFD1	Q04458.1	2494079	Saccharomyces cerevisiae
GOR1	NP_014125.1	6324055	Saccharomyces cerevisiae
YPL113C	AAB68248.1	1163100	Saccharomyces cerevisiae
GCY1	CAA99318.1	1420317	Saccharomyces cerevisiae

Ketone reductase or alcohol dehydrogenase enzymes that reduce 3-oxoacyl-CoA substrates to their corresponding 3-hyroxyacyl-CoA product are relevant to the pathways depicted in FIG. 2. 3-Oxoacyl-CoA reductase enzymes (EC 1.1.1.35) convert 3-oxoacyl-CoA molecules into 3-hydroxyacyl-CoA molecules and are often involved in fatty acid beta-oxidation or phenylacetate catabolism. For example, subunits of two fatty acid oxidation complexes in E. coli, encoded by fadB and fadJ, function as 3-hydroxyacyl-CoA dehydrogenases (Binstock et al., Methods Enzymol. 71 Pt C:403-411 (1981)). Given the proximity in E. coli of paaH to other genes in the phenylacetate degradation operon (Nogales et al., 153:357-365 (2007)) and the fact that paaH mutants cannot grow on phenylacetate (Ismail et al., Eur. J Biochem. 270:3047-3054 (2003)), it is expected that the E. coli paaH gene also encodes a 3-hydroxyacyl-CoA dehydrogenase. Additional 3-oxoacyl-CoA enzymes include the gene products of phaC in Pseudomonas putida (Olivera et al., Proc. Natl. Acad. Sci U.S.A 95:6419-6424 (1998)) and paaC in Pseudomonas fluorescens (Di et al., 188:117-125 (2007)). These enzymes catalyze the reversible oxidation of 3-hydroxyadipyl-CoA to 3-oxoadipyl-CoA during the catabolism of phenylacetate or styrene.
Acetoacetyl-CoA reductase participates in the acetyl-CoA fermentation pathway to butyrate in several species of Clostridia and has been studied in detail (Jones et al., Microbiol Rev. 50:484-524 (1986)). The enzyme from Clostridium acetobutylicum, encoded by hbd, has been cloned and functionally expressed in E. coli (Youngleson et al., J Bacteriol. 171:6800-6807 (1989)). Yet other genes demonstrated to reduce acetoacetyl-CoA to 3-hydroxybutyryl-CoA are phbB from Zoogloea ramigera (Ploux et al., Eur. J Biochem. 174:177-182 (1988)) and phaB from Rhodobacter sphaeroides (Alber et al., Mol. Microbiol 61:297-309 (2006)). The former gene is NADPH-dependent, its nucleotide sequence has been determined (Peoples et al., Mol. Microbiol 3:349-357 (1989)) and the gene has been expressed in E. coli. Substrate specificity studies on the gene led to the conclusion that it could accept 3-oxopropionyl-CoA as a substrate besides acetoacetyl-CoA (Ploux et al., Eur. J Biochem. 174:177-182 (1988)). Additional genes include phaB in Paracoccus denitrificans, Hbd1 (C-terminal domain) and Hbd2 (N-terminal domain) in Clostridium kluyveri (Hillmer and Gottschalk, Biochim. Biophys. Acta 3334:12-23 (1974)) and HSD17B10 in Bos taurus (Wakil et al., J Biol. Chem. 207:631-638 (1954)). The enzyme from Paracoccus denitrificans has been functionally expressed and characterized in E. coli (Yabutani et al., FEMS Microbiol Lett. 133:85-90 (1995)). A number of similar enzymes have been found in other species of Clostridia and in Metallosphaera sedula (Berg et al., Science. 318:1782-1786 (2007)). The enzyme from Candida tropicalis is a component of the peroxisomal fatty acid beta-oxidation multifunctional enzyme type 2 (MFE-2). The dehydrogenase B domain of this protein is catalytically active on acetoacetyl-CoA. The domain has been functionally expressed in E. coli, a crystal structure is available, and the catalytic mechanism is well-understood (Ylianttila et al., Biochem Biophys Res Commun 324:25-30 (2004); Ylianttila et al., J Mol Biol 358:1286-1295 (2006)).


Protein	Genbank ID	GI number	Organism

fadB	P21177.2	119811	Escherichia coli
fadJ	P77399.1	3334437	Escherichia coli
paaH	NP_415913.1	16129356	Escherichia coli
Hbd2	EDK34807.1	146348271	Clostridium kluyveri
Hbd1	EDK32512.1	146345976	Clostridium kluyveri
phaC	NP_745425.1	26990000	Pseudomonas putida
paaC	ABF82235.1	106636095	Pseudomonas fluorescens
HSD17B10	O02691.3	3183024	Bos taurus
phbB	P23238.1	130017	Zoogloea ramigera
phaB	YP_353825.1	77464321	Rhodobacter sphaeroides
phaB	BAA08358	675524	Paracoccus denitrificans
Hbd	NP_349314.1	15895965	Clostridium
			acetobutylicum
Hbd	AAM14586.1	20162442	Clostridium beijerinckii
Msed_1423	YP_001191505	146304189	Metallosphaera sedula
Msed_0399	YP_001190500	146303184	Metallosphaera sedula
Msed_0389	YP_001190490	146303174	Metallosphaera sedula
Msed_1993	YP_001192057	146304741	Metallosphaera sedula
Fox2	Q02207	399508	Candida tropicalis

The conversion of cyclohexane-1,2-dione to a diol can be accomplished by cyclohexane-1,2-diol dehydrogenase (EC 1.1.1.174). This enzymatic activity has been demonstrated in Acinetobacter TD63 (Davey et al., Eur. J Biochem. 74:115-127 (1977)). It has been indicated that cyclohexanol dehydrogenase (EC 1.1.1.245), an enzyme with a broad substrate range, can catalyze these conversions. Cyclohexanol dehydrogenase enzymes from Rhodococcus sp TK6 (Tae-Kang et al., J. Microbiol. Biotechnol. 12:39-45 (2002)), a denitrifying Pseudomonas sp. (Dangel et al., 152:271-279 (1989)), Nocardia sp (Stirling et al., 4:37-40 (1980)) and Xanthobacter sp. (Trower et al., 49:1282-1289 (1985)) have all been shown to convert cyclohexan-1,2-diol to cyclohexan-1,2-dione. The gene associated with a cyclohexanol dehydrogenase in Acinetobacter sp NCIMB9871 was identified in 2000 (Cheng et al., J Bacteriol. 182:4744-4751 (2000)). This enzyme, encoded by chnA, has not been tested for activity on cyclohexan-1,2-dione or cyclohexan-1,2-diol. A BLAST comparison of the Acinetobacter ChnA protein sequence identifies genes from other organisms including Ralstonia metallireducens (57% identity), and Pseudomona sputida (47% identity). A cyclohexanol dehydrogenase gene from Comamonas testosteroni has also been expressed and characterized in E. coli (Van Beilen et al., 5:174-182 (2003)); a similar gene was also identified in Xanthobacter flavus (Van Beilen et al., Environ. Microbiol 5:174-182 (2003)). The protein sequences for exemplary gene products can be found using the following GenBank accession numbers shown below.


Protein	GenBank ID	GI Number	Organism

chnA	BAC80215.1	33284995	Acinetobacter
			sp NCIMB9871
chnA	CAD10799.1	16943680	Comamonas testosteroni
chnA	CAD10802.1	18495819	Xanthobacter flavus
Rmet_1335	YP_583487.1	94310277	Ralstonia metallireducens
PP_1946	NP_744098.1	26988673	Pseudomonas putida

Another enzyme which can accomplish this conversion is diacetyl reductase (EC 1.1.1.5). Naturally catalyzing the conversion of diacetyl (2,3-butanedione) to acetoin and subsequent reduction to 2,3-butanediol, two NADPH-dependent diacetyl reductase enzymes from S. cerevisiae have been shown to also accept cyclohexan-1,2-dione as a substrate (Heidlas et al., Eur. J Biochem. 188:165-174 (1990)). The (S)-specific NADPH-dependent diacetyl reductase from this study was later identified as D-arabinose dehydrogenase, the gene product of ARA1 (Katz et al., 33:163-172 (2003)). The NADH-dependent gene product of BDH1 of S. cerevisiae also has diacetyl reductase functionality (Gonzalez et al., 275:35876-35885 (2000)). Several other enzymes with diketone reductase functionality have been identified in yeast, encoded by genes GCY1, YPR1, GRE3, YJR036c (Johanson et al., FEMS Yeast Res. 5:513-525 (2005)). The protein sequences for exemplary gene products can be found using the following GenBank accession numbers shown below.


Protein	GenBank ID	GI Number	Organism

ARA1	NP_009707.1	6319625	Saccharomyces cerevisiae
BDH1	NP_009341.1	6319258	Saccharomyces cerevisiae
GCY1	NP_014763.1	6324694	Saccharomyces cerevisiae
YPR1	NP_010656.1	6320576	Saccharomyces cerevisiae
GRE3	NP_011972.1	6321896	Saccharomyces cerevisiae
YIR036c	AAS56566.1	45270370	Saccharomyces cerevisiae

1.2.1.b Oxidoreductase (acyl-CoA to Aldehyde)

An adipyl-CoA reductase converts adipyl-CoA to adipate semialdehyde in Step A of FIG. 1. Several acyl-CoA reductase enzymes are found in EC class 1.2.1. Exemplary enzymes include fatty acyl-CoA reductase, succinyl-CoA reductase (EC 1.2.1.76), acetyl-CoA reductase, butyryl-CoA reductase and propionyl-CoA reductase (EC 1.2.1.3). Exemplary fatty acyl-CoA reductases enzymes are encoded by acrl of Acinetobacter calcoaceticus (Reiser, Journal of Bacteriology 179:2969-2975 (1997)) and Acinetobacter sp. M-1 (Ishige et al., Appl. Environ. Microbiol. 68:1192-1195 (2002)). Enzymes with succinyl-CoA reductase activity are encoded by sucD of Clostridium kluyveri (Sohling, J. Bacteriol. 178:871-880 (1996)) and sucD of P. gingivalis (Takahashi, J. Bacteriol 182:4704-4710 (2000)). Additional succinyl-CoA reductase enzymes participate in the 3-hydroxypropionate/4-hydroxybutyrate cycle of thermophilic archaea including Metallosphaera sedula (Berg et al., Science 318:1782-1786 (2007)) and Thermoproteus neutrophilus (Ramos-Vera et al., J Bacteriol, 191:4286-4297 (2009)). The M. sedula enzyme, encoded by Msed_0709, is strictly NADPH-dependent and also has malonyl-CoA reductase activity. The T. neutrophilus enzyme is active with both NADPH and NADH. The enzyme acylating acetaldehyde dehydrogenase in Pseudomonas sp, encoded by bphG, is yet another as it has been demonstrated to oxidize and acylate acetaldehyde, propionaldehyde, butyraldehyde, isobutyraldehyde and formaldehyde (Powlowski, J. Bacteriol. 175:377-385 (1993)). In addition to reducing acetyl-CoA to ethanol, the enzyme encoded by adhE in Leuconostoc mesenteroides has been shown to oxidize the branched chain compound isobutyraldehyde to isobutyryl-CoA (Kazahaya, J. Gen. Appl. Microbiol. 18:43-55 (1972); and Koo et al., Biotechnol Lett. 27:505-510 (2005)). Butyraldehyde dehydrogenase catalyzes a similar reaction, conversion of butyryl-CoA to butyraldehyde, in solventogenic organisms such as Clostridium saccharoperbutylacetonicum (Kosaka et al., Biosci Biotechnol Biochem., 71:58-68 (2007)). Exemplary propionyl-CoA reductase enzymes include pduP of Salmonella typhimurium LT2 (Leal, Arch. Microbiol. 180:353-361 (2003)) and eutE from E. coli (Skraly, WO Patent No. 2004/024876). The propionyl-CoA reductase of Salmonella typhimurium LT2, which naturally converts propionyl-CoA to propionaldehyde, also catalyzes the reduction of 5-hydroxyvaleryl-CoA to 5-hydroxypentanal (WO 2010/068953A2).


Protein	GenBank ID	GI Number	Organism

acr

1	YP_047869.1	50086359	Acinetobacter
			calcoaceticus
acr 1	AAC45217	1684886	Acinetobacter baylyi
acr 1	BAB85476.1	18857901	Acinetobacter
			sp. Strain M-1
Msed_0709	YP_001190808.1	146303492	Metallosphaera sedula
Tneu_0421	ACB39369.1	170934108	Thermoproteus
			neutrophilus
sucD	P38947.1	172046062	Clostridium kluyveri
sucD	NP_904963.1	34540484	Porphyromonas
			gingivalis
bphG	BAA03892.1	425213	Pseudomonas sp
adhE	AAV66076.1	55818563	Leuconostoc
			mesenteroides
bld	AAP42563.1	31075383	Clostridium
			saccharoperbu-
			tylacetonicum
pduP	NP_460996	16765381	Salmonella typhimurium
			LT2
eutE	NP_416950	16130380	Escherichia coli

An additional enzyme type that converts an acyl-CoA to its corresponding aldehyde is malonyl-CoA reductase which transforms malonyl-CoA to malonic semialdehyde. Malonyl-CoA reductase is a key enzyme in autotrophic carbon fixation via the 3-hydroxypropionate cycle in thermoacidophilic archaeal bacteria (Berg, Science 318:1782-1786 (2007); and Thauer, Science 318:1732-1733 (2007)). The enzyme utilizes NADPH as a cofactor and has been characterized in Metallosphaera and Sulfolobus sp. (Alber et al., J. Bacteriol. 188:8551-8559 (2006); and Hugler, J. Bacteriol. 184:2404-2410 (2002)). The enzyme is encoded by Msed_0709 in Metallosphaera sedula (Alber et al., J. Bacteriol. 188:8551-8559 (2006); and Berg, Science 318:1782-1786 (2007)). A gene encoding a malonyl-CoA reductase from Sulfolobus tokodaii was cloned and heterologously expressed in E. coli (Alber et al., J. Bacteriol 188:8551-8559 (2006). This enzyme has also been shown to catalyze the conversion of methylmalonyl-CoA to its corresponding aldehyde (WO2007141208 (2007)). Although the aldehyde dehydrogenase functionality of these enzymes is similar to the bifunctional dehydrogenase from Chloroflexus aurantiacus, there is little sequence similarity. Both malonyl-CoA reductase enzyme candidates have high sequence similarity to aspartate-semialdehyde dehydrogenase, an enzyme catalyzing the reduction and concurrent dephosphorylation of aspartyl-4-phosphate to aspartate semialdehyde. Additional gene candidates can be found by sequence homology to proteins in other organisms including Sulfolobus solfataricus and Sulfolobus acidocaldarius and have been listed below. Yet another candidate for CoA-acylating aldehyde dehydrogenase is the aid gene from Clostridium beijerinckii (Toth, Appl. Environ. Microbiol. 65:4973-4980 (1999). This enzyme has been reported to reduce acetyl-CoA and butyryl-CoA to their corresponding aldehydes. This gene is very similar to eutE that encodes acetaldehyde dehydrogenase of Salmonella typhimurium and E. coli (Toth, Appl. Environ. Microbiol. 65:4973-4980 (1999).


Gene	GenBank ID	GI Number	Organism

Msed_0709	YP_001190808.1	146303492	Metallosphaera sedula
mcr	NP_378167.1	15922498	Sulfolobus tokodaii
asd-2	NP_343563.1	15898958	Sulfolobus solfataricus
Saci_2370	YP_256941.1	70608071	Sulfolobus
			acidocaldarius
Ald	AAT66436	49473535	Clostridium beijerinckii
eutE	AAA80209	687645	Salmonella typhimurium
eutE	NP_416950	16130380	Escherichia coli

1.2.1.e (CAR)

The conversion of an acid to an aldehyde is thermodynamically unfavorable and typically requires energy-rich cofactors and multiple enzymatic steps. For example, in butanol biosynthesis conversion of butyrate to butyraldehyde is catalyzed by activation of butyrate to its corresponding acyl-CoA by a CoA transferase or ligase, followed by reduction to butyraldehyde by a CoA-dependent aldehyde dehydrogenase. Alternately, an acid can be activated to an acyl-phosphate and subsequently reduced by a phosphate reductase. Direct conversion of the acid to aldehyde by a single enzyme is catalyzed by a bifunctional enzyme in the 1.2.1 family. Exemplary enzymes that catalyze these transformations include carboxylic acid reductase, alpha-aminoadipate reductase and retinoic acid reductase.
Carboxylic acid reductase (CAR), found in Nocardia iowensis, catalyzes the magnesium, ATP and NADPH-dependent reduction of carboxylic acids to their corresponding aldehydes (Venkitasubramanian et al., J Biol. Chem. 282:478-485 (2007)). The natural substrate of this enzyme is benzoic acid and the enzyme exhibits broad acceptance of aromatic and aliphatic substrates (Venkitasubramanian et al., Biocatalysis in Pharmaceutical and Biotechnology Industries. CRC press (2006)). This enzyme, encoded by car, was cloned and functionally expressed in E. coli (Venkitasubramanian et al., J Biol. Chem. 282:478-485 (2007)). CAR requires post-translational activation by a phosphopantetheine transferase (PPTase) that converts the inactive apo-enzyme to the active holo-enzyme (Hansen et al., Appl. Environ. Microbiol 75:2765-2774 (2009)). Expression of the npt gene, encoding a specific PPTase, product improved activity of the enzyme. An enzyme with similar characteristics, alpha-aminoadipate reductase (AAR, EC 1.2.1.31), participates in lysine biosynthesis pathways in some fungal species. This enzyme naturally reduces alpha-aminoadipate to alpha-aminoadipate semialdehyde. The carboxyl group is first activated through the ATP-dependent formation of an adenylate that is then reduced by NAD(P)H to yield the aldehyde and AMP. Like CAR, this enzyme utilizes magnesium and requires activation by a PPTase. Enzyme candidates for AAR and its corresponding PPTase are found in Saccharomyces cerevisiae (Morris et al., Gene 98:141-145 (1991)), Candida albicans (Guo et al., Mol. Genet. Genomics 269:271-279 (2003)), and Schizosaccharomyces pombe (Ford et al., Curr. Genet. 28:131-137 (1995)). The AAR from S. pombe exhibited significant activity when expressed in E. coli (Guo et al., Yeast 21:1279-1288 (2004)). The AAR from Penicillium chrysogenum accepts S-carboxymethyl-L-cysteine as an alternate substrate, but did not react with adipate, L-glutamate or diaminopimelate (Hijarrubia et al., J Biol. Chem. 278:8250-8256 (2003)). The gene encoding the P. chrysogenum PPTase has not been identified to date and no high-confidence hits were identified by sequence comparison homology searching.


Protein	GenBank ID	GI Number	Organism

car	AAR91681.1	40796035	Nocardia iowensis
npt	ABI83656.1	114848891	Nocardia iowensis
LYS2	AAA34747.1	171867	Saccharomyces cerevisiae
LYS5	P50113.1	1708896	Saccharomyces cerevisiae
LYS2	AAC02241.1	2853226	Candida albicans
LYS5	AAO26020.1	28136195	Candida albicans
Lys1p	P40976.3	13124791	Schizosaccharomyces pombe
Lys7p	Q10474.1	1723561	Schizosaccharomyces pombe
Lys2	CAA74300.1	3282044	Penicillium chrysogenum

Additional car and npt genes can be identified based on sequence homology.


Gene name	GenBank ID	GI Number	Organism

fadD9	YP_978699.1	121638475	Mycobacterium bovis BCG
BCG_2812c	YP_978898.1	121638674	Mycobacterium bovis BCG
nfa20150	YP_118225.1	54023983	Nocardia farcinica IFM
			10152
nfa40540	YP_120266.1	54026024	Nocardia farcinica IFM
			10152
SGR_6790	YP_001828302.1	182440583	Streptomyces griseus subsp.
			griseus NBRC 13350
SGR_665	YP_001822177.1	182434458	Streptomyces griseus subsp.
			griseus NBRC 13350
MSMEG_2956	YP_887275.1	118473501	Mycobacterium smegmatis
			MC2 155
MSMEG_5739	YP_889972.1	118469671	Mycobacterium smegmatis
			MC2 155
MSMEG_2648	YP_886985.1	118471293	Mycobacterium smegmatis
			MC2 155
MAP1040c	NP_959974.1	41407138	Mycobacterium avium
			subsp. paratuberculosis K-
			10
MAP2899c	NP_961833.1	41408997	Mycobacterium avium
			subsp. paratuberculosis K-
			10
MMAR_2117	YP_001850422.1	183982131	Mycobacterium marinum M
MMAR_2936	YP_001851230.1	183982939	Mycobacterium marinum M
MMAR_1916	YP_001850220.1	183981929	Mycobacterium marinum M
Tpau_1373	YP_003646340.1	296139097	Tsukamurella
			paurometabola DSM 20162
Tpau_1726	YP_003646683.1	296139440	Tsukamurella
			paurometabola DSM 20162
CPCC7001_1320	ZP_05045132.1	254431429	Cyanobium PCC7001
DDBDRAFT_0187729	XP_636931.1	66806417	Dictyostelium discoideum
			AX4

An additional enzyme candidate found in Streptomyces griseus is encoded by the griC and griD genes. This enzyme is believed to convert 3-amino-4-hydroxybenzoic acid to 3-amino-4-hydroxybenzaldehyde as deletion of either griC or griD led to accumulation of extracellular 3-acetylamino-4-hydroxybenzoic acid, a shunt product of 3-amino-4-hydroxybenzoic acid metabolism (Suzuki, et al., J. Antibiot. 60(6):380-387 (2007)). Co-expression of griC and griD with SGR_665, an enzyme similar in sequence to the Nocardia iowensis npt, can be beneficial.


	GenBank
Gene name	Accession No.	GI Number	Organism

griC	YP_001825755.1	182438036	Streptomyces griseus
			subsp.
			griseus NBRC 13350
griD	YP_001825756.1	182438037	Streptomyces griseus
			subsp.
			griseus NBRC 13350

1.14.13.a Monooxygenase

Oxidation of cyclohexanone to caprolactone, shown FIG. 3, is catalyzed by cyclohexanone monooxygenase (EC 1.14.13.22). The enzyme encoded by chnB of Acinetobacter sp. NCIMB9871 has been extensively studied and it has been overexpressed. Improved expression was obtained when the chnB gene was overexpressed in tandem with its regulator, chnR (Iwaki et al, AEM 65:5158-62 (1999)). Similar enzymes have been characterized in Acinetobacter calcoaceticus, Rhodococcus sp. Phi2 and Phi1, Xanthobacter flavus and Acinetobacter sp. SE19 (Doo et al, J Biotechnol 142:164-9 (2009); Brzostowicz et al, AEM 69:334-42 (2003)). Accession numbers of cyclohexanone monooxygenase enzymes and transcriptional regulators are shown in the table below.


Gene	GenBank ID	GI Number	Organism

chnB	BAA86293.1	6277322	Acinetobacter sp. NCIMB9871
chnB	P12015.2	118066	Acinetobacter calcoaceticus
chnB	AAN37494.1	27657637	Rhodococcus sp. Phi1
chnB	AAN37491.1	27657633	Rhodococcus sp. Phi2
chnB	CAD10801.1	18495818	Xanthobacter flavus
chnB	AAG10026.1	9965291	Acinetobacter sp. SE19
chnR	BAA86295.1	6277324	Acinetobacter sp. NCIMB9871
chnR	BAA19366	1881339	Bacillus subtilis
chnR	AAK73166	14719380	Brevibacerium sp. HCU
chnR	ADY81661.1	325122138	Acinetobacter calcoaceticus
chnR	AAN37488.1	27657630	Rhodococcus sp. Phi2
chnR	AAN37481.1	27657622	Arthrobacter sp. BP2

2.3.1.a Acyltransferase (Transferring Phosphate Group)

An enzyme with phosphotrans-6-hydroxyhexanoylase activity is required to convert 6-hydroxyhexanoyl-CoA to 6-hydroxyhexanoyl phosphate (Step J of FIG. 1 and Step H of FIG. 2). Exemplary phosphate-transferring acyltransferases include phosphotransacetylase (EC 2.3.1.8) and phosphotransbutyrylase (EC 2.3.1.19). The pta gene from E. coli encodes a phosphotransacetylase that reversibly converts acetyl-CoA into acetyl-phosphate (Suzuki, Biochim. Biophys. Acta 191:559-569 (1969)). This enzyme can also utilize propionyl-CoA as a substrate, forming propionate in the process (Hesslinger et al., Mol. Microbiol 27:477-492 (1998)). Other phosphate acetyltransferases that exhibit activity on propionyl-CoA are found in Bacillus subtilis (Rado et al., Biochim. Biophys. Acta 321:114-125 (1973)), Clostridium kluyveri (Stadtman, Methods Enzymol 1:596-599 (1955)), and Thermotoga maritima (Bock et al., J Bacteriol. 181:1861-1867 (1999)). Similarly, the ptb gene from C. acetobutylicum encodes phosphotransbutyrylase, an enzyme that reversibly converts butyryl-CoA into butyryl-phosphate (Wiesenborn et al., Appl Environ. Microbiol 55:317-322 (1989); Walter et al., Gene 134:107-111 (1993)). Additional ptb genes are found in butyrate-producing bacterium L2-50 (Louis et al., J. Bacteriol. 186:2099-2106 (2004)) and Bacillus megaterium (Vazquez et al., Curr. Microbiol 42:345-349 (2001)).


Protein	GenBank ID	GI Number	Organism

pta	NP_416800.1	71152910	Escherichia coli
pta	P39646	730415	Bacillus subtilis
pta	A5N801	146346896	Clostridium kluyveri
pta	Q9X0L4	6685776	Thermotoga maritima
ptb	NP_349676	34540484	Clostridium acetobutylicum
ptb	AAR19757.1	38425288	butyrate-producing
			bacterium L2-50
ptb	CAC07932.1	10046659	Bacillus megaterium

2.3.1.b Beta-Ketothiolase

Beta-ketothiolase enzymes in the EC class 2.3.1 catalyze the condensation of two acyl-CoA substrates. Step A of FIG. 2 requires a beta-ketothiolase to catalyze the condensation of 4-hydroxybutyryl-CoA and acetyl-CoA into 3-oxo-6-hydroxyhexanoyl-CoA. Although this transformation has not been demonstrated in the literature to date, suitable enzymes include 3-oxoadipyl-CoA thiolase (EC 2.3.1.174), acetoacetyl-CoA thiolase (EC 2.3.1.9) and 3-oxopimeloyl-CoA thiolase (EC 2.3.1.16).
3-Oxoadipyl-CoA thiolase (EC 2.3.1.174) converts beta-ketoadipyl-CoA to succinyl-CoA and acetyl-CoA, and is a key enzyme of the beta-ketoadipate pathway for aromatic compound degradation. The enzyme is widespread in soil bacteria and fungi including Pseudomonas putida (Harwood et al., J Bacteriol. 176:6479-6488 (1994)) and Acinetobacter calcoaceticus (Doten et al., J Bacteriol. 169:3168-3174 (1987)). The gene products encoded by pcaF in Pseudomonas strain B13 (Kaschabek et al., J Bacteriol. 184:207-215 (2002)), phaD in Pseudomonas putida U (Olivera et al., Proc. Natl. Acad. Sci U.S.A 95:6419-6424 (1998)), paaE in Pseudomonas fluorescens ST (Di et al., Arch. Microbiol 188:117-125 (2007)), and paaJ from E. coli (Nogales et al., Microbiology 153:357-365 (2007)) also catalyze this transformation. Several beta-ketothiolases exhibit significant and selective activities in the oxoadipyl-CoA forming direction including bkt from Pseudomonas putida, pcaF and bkt from Pseudomonas aeruginosa PAO1, bkt from Burkholderia ambifaria AMMD, paaJ from E. coli, and phaD from P. putida.


Gene name	GI number	GenBank ID	Organism

paaJ	16129358	NP_415915.1	Escherichia coli
pcaF	17736947	AAL02407	Pseudomonas knackmussii
			(B13)
phaD	3253200	AAC24332.1	Pseudomonas putida
pcaF	506695	AAA85138.1	Pseudomonas putida
pcaF	141777	AAC37148.1	Acinetobacter calcoaceticus
paaE	106636097	ABF82237.1	Pseudomonas fluorescens
bkt	115360515	YP_777652.1	Burkholderia ambifaria
			AMMD
bkt	9949744	AAG06977.1	Pseudomonas aeruginosa
			PAO1
pcaF	9946065	AAG03617.1	Pseudomonas aeruginosa
			PAO1

Glutaryl-CoA and acetyl-CoA are condensed to form 3-oxopimeloyl-CoA by oxopimeloyl-CoA:glutaryl-CoA acyltransferase, a beta-ketothiolase (EC 2.3.1.16). An enzyme catalyzing this transformation is found in Ralstonia eutropha (formerly known as Alcaligenes eutrophus), encoded by genes bktB and bktC (Slater et al., J. Bacteriol. 180:1979-1987 (1998); Haywood et al., FEMS Microbiology Letters 52:91-96 (1988)). The sequence of the BktB protein is known; however, the sequence of the BktC protein has not been reported. The pim operon of Rhodopseudomonas palustris also encodes a beta-ketothiolase, encoded by pimB, predicted to catalyze this transformation in the degradative direction during benzoyl-CoA degradation (Harrison et al., Microbiology 151:727-736 (2005)). A beta-ketothiolase enzyme candidate in S. aciditrophicus was identified by sequence homology to bktB (43% identity, evalue=1e-93).


Protein	GenBank ID	GI Number	Organism

bktB	YP_725948	11386745	Ralstonia eutropha
pimB	CAE29156	39650633	Rhodopseudomonas
			palustris
syn_02642	YP_462685.1	85860483	Syntrophus aciditrophicus

Acetoacetyl-CoA thiolase converts two molecules of acetyl-CoA into acetoacetyl-CoA (EC 2.1.3.9). This activity is encoded by atoB from E. coli (Martin et al., Nat. Biotechnol 21:796-802 (2003)), thlA and thlB from Clostridium acetobutylicum (Hanai et al., Appl Environ Microbiol 73:7814-7818 (2007); Winzer et al., J. Mol. Microbiol Biotechnol 2:531-541 (2000)), and ERG10 from S. cerevisiae (Hiser et al., J. Biol. Chem. 269:31383-31389 (1994)).


Protein	GenBank ID	GI Number	Organism

atoB	NP_416728	16130161	Escherichia coli
thlA	NP_349476.1	15896127	Clostridium acetobutylicum
thlB	NP_149242.1	15004782	Clostridium acetobutylicum
ERG10	NP_015297	6325229	Saccharomyces cerevisiae

Beta-ketothiolase enzymes catalyzing the formation of beta-ketovalerate from acetyl-CoA and propionyl-CoA may also be able to catalyze the formation of 3-oxo-6-hydroxyhexanoyl-CoA. Zoogloea ramigera possesses two ketothiolases that can form 3-ketovaleryl-CoA from propionyl-CoA and acetyl-CoA and R. eutropha has a beta-oxidation ketothiolase that is also capable of catalyzing this transformation (Gruys et al., U.S. Pat. No. 5,958,745 (1999)). The sequences of these genes or their translated proteins have not been reported, but several candidates in R. eutropha, Z. ramigera, or other organisms can be identified based on sequence homology to bktB from R. eutropha. These include:


Protein	GenBank ID	GI Number	Organism

phaA	YP_725941.1	113867452	Ralstonia eutropha
h16_A1713	YP_726205.1	113867716	Ralstonia eutropha
pcaF	YP_728366.1	116694155	Ralstonia eutropha
h16_B1369	YP_840888.1	116695312	Ralstonia eutropha
h16_A0170	YP_724690.1	113866201	Ralstonia eutropha
h16_A0462	YP_724980.1	113866491	Ralstonia eutropha
h16_A1528	YP_726028.1	113867539	Ralstonia eutropha
h16_B0381	YP_728545.1	116694334	Ralstonia eutropha
h16_B0662	YP_728824.1	116694613	Ralstonia eutropha
h16_B0759	YP_728921.1	116694710	Ralstonia eutropha
h16_B0668	YP_728830.1	116694619	Ralstonia eutropha
h16_A1720	YP_726212.1	113867723	Ralstonia eutropha
h16_A1887	YP_726356.1	113867867	Ralstonia eutropha
phbA	P07097.4	135759	Zoogloea ramigera
bktB	YP_002005382.1	194289475	Cupriavidus taiwanensis
Rmet_1362	YP_583514.1	94310304	Ralstonia metallidurans
Bphy_0975	YP_001857210.1	186475740	Burkholderia phymatum

2.7.2.a Phosphotransferase (Carboxy Group Acceptor)

Kinase or phosphotransferase enzymes in the EC class 2.7.2 transform carboxylic acids to phosphonic acids with concurrent hydrolysis of one ATP. Such an enzyme is required for the phosphorylation of 6-hydroxyhexanoate depicted in Step H of FIG. 1 and Step J of FIG. 2. Exemplary enzyme candidates include butyrate kinase (EC 2.7.2.7), isobutyrate kinase (EC 2.7.2.14), aspartokinase (EC 2.7.2.4), acetate kinase (EC 2.7.2.1), glycerate kinase (EC 2.7.1.31) and gamma-glutamyl kinase (EC 2.7.2.11). Butyrate kinase catalyzes the reversible conversion of butyryl-phosphate to butyrate during acidogenesis in Clostridial species (Cary et al., Appl Environ Microbiol 56:1576-1583 (1990)). The Clostridium acetobutylicum enzyme is encoded by either of the two buk gene products (Huang et al., J Mol. Microbiol Biotechnol 2:33-38 (2000)). Other butyrate kinase enzymes are found in C. butyricum and C. tetanomorphum (Twarog et al., J Bacteriol. 86:112-117 (1963)). A related enzyme, isobutyrate kinase from Thermotoga maritima, was expressed in E. coli and crystallized (Diao et al., J Bacteriol. 191:2521-2529 (2009); Diao et al., Acta Crystallogr. D. Biol. Crystallogr. 59:1100-1102 (2003)). Aspartokinase catalyzes the ATP-dependent phosphorylation of aspartate and participates in the synthesis of several amino acids. The aspartokinase III enzyme in E. coli, encoded by lysC, has a broad substrate range and the catalytic residues involved in substrate specificity have been elucidated (Keng et al., Arch Biochem Biophys 335:73-81 (1996)). Two additional kinases in E. coli are also acetate kinase and gamma-glutamyl kinase. The E. coli acetate kinase, encoded by ackA (Skarstedt et al., J. Biol. Chem. 251:6775-6783 (1976)), phosphorylates propionate in addition to acetate (Hesslinger et al., Mol. Microbiol 27:477-492 (1998)). The E. coli gamma-glutamyl kinase, encoded by proB (Smith et al., J. Bacteriol. 157:545-551 (1984)), phosphorylates the gamma carbonic acid group of glutamate.


Protein	GenBank ID	GI Number	Organism

buk1	NP_349675	15896326	Clostridium acetobutylicum
buk2	Q97II1	20137415	Clostridium acetobutylicum
buk2	Q9X278.1	6685256	Thermotoga maritima
lysC	NP_418448.1	16131850	Escherichia coli
ackA	NP_416799.1	16130231	Escherichia coli
proB	NP_414777.1	16128228	Escherichia coli

Acetylglutamate kinase phosphorylates acetylated glutamate during arginine biosynthesis. This enzyme is not known to accept alternate substrates; however, several residues of the E. coli enzyme involved in substrate binding and phosphorylation have been elucidated by site-directed mutagenesis (Marco-Marin et al., 334:459-476 (2003); Ramon-Maiques et al., Structure. 10:329-342 (2002)). The enzyme is encoded by argB in Bacillus subtilis and E. coli (Parsot et al., Gene 68:275-283 (1988)), and ARG5,6 in S. cerevisiae (Pauwels et al., Eur. J Biochem. 270:1014-1024 (2003)). The ARG5,6 gene of S. cerevisiae encodes a polyprotein precursor that is matured in the mitochondrial matrix to become acetylglutamate kinase and acetylglutamylphosphate reductase.


Protein	GenBank ID	GI Number	Organism

argB	NP_418394.3	145698337	Escherichia coli
argB	NP_389003.1	16078186	Bacillus subtilis
ARG5,6	NP_010992.1	6320913	Saccharomyces cerevisiae

Glycerate kinase (EC 2.7.1.31) activates glycerate to glycerate-2-phosphate or glycerate-3-phosphate. Three classes of glycerate kinase have been identified. Enzymes in class I and II produce glycerate-2-phosphate, whereas the class III enzymes found in plants and yeast produce glycerate-3-phosphate (Bartsch et al., FEBS Lett. 582:3025-3028 (2008)). In a recent study, class III glycerate kinase enzymes from Saccharomyces cerevisiae, Oryza sativa and Arabidopsis thaliana were heterologously expressed in E. coli and characterized (Bartsch et al., FEBS Lett. 582:3025-3028 (2008)). This study also assayed the glxK gene product of E. coli for ability to form glycerate-3-phosphate and found that the enzyme can only catalyze the formation of glycerate-2-phosphate, in contrast to previous work (Doughty et al., J Biol. Chem. 241:568-572 (1966)).


Protein	GenBank ID	GI Number	Organism

glxK	AAC73616.1	1786724	Escherichia coli
YGR205W	AAS56599.1	45270436	Saccharomyces cerevisiae
Os01g0682500	BAF05800.1	113533417	Oryza sativa
Atlg80380	BAH57057.1	227204411	Arabidopsis thaliana

2.8.3.a CoA Transferase

CoA transferases catalyze the reversible transfer of a CoA moiety from one molecule to another. Several transformations require a CoA transferase to interconvert carboxylic acids and their corresponding acyl-CoA derivatives, including steps C and F of FIG. 1, step E of FIG. 2 and step B of FIG. 5. CoA transferase enzymes have been described in the open literature and represent suitable candidates for these steps. These are described below.
Many transferases have broad specificity and thus can utilize CoA acceptors as diverse as acetate, succinate, propionate, butyrate, 2-methylacetoacetate, 3-ketohexanoate, 3-ketopentanoate, valerate, crotonate, 3-mercaptopropionate, propionate, vinylacetate, butyrate, among others. For example, an enzyme from Roseburia sp. A2-183 was shown to have butyryl-CoA:acetate:CoA transferase and propionyl-CoA:acetate:CoA transferase activity (Charrier et al., Microbiology 152, 179-185 (2006)). Close homologs can be found in, for example, Roseburia intestinalis L1-82, Roseburia inulinivorans DSM 16841, Eubacterium rectale ATCC 33656. Another enzyme with propionyl-CoA transferase activity can be found in Clostridium propionicum (Selmer et al., Eur J Biochem 269, 372-380 (2002)). This enzyme can use acetate, (R)-lactate, (S)-lactate, acrylate, and butyrate as the CoA acceptor (Selmer et al., Eur J Biochem 269, 372-380 (2002); Schweiger and Buckel, FEBS Letters, 171(1) 79-84 (1984)). Close homologs can be found in, for example, Clostridium novyi NT, Clostridium beijerinckii NCIMB 8052, and Clostridium botulinum C str. Eklund. YgfH encodes a propionyl CoA:succinate CoA transferase in E. coli (Haller et al., Biochemistry, 39(16) 4622-4629). Close homologs can be found in, for example, Citrobacter youngae ATCC 29220, Salmonella enterica subsp. arizonae serovar, and Yersinia intermedia ATCC 29909. These proteins are identified below.


Protein	GenBank ID	GI Number	Organism

Ach1	AAX19660.1	60396828	Roseburia
			sp. A2-183
ROSINTL182_07121	ZP_04743841.2	257413684	Roseburia
			intestinalis
ROSEINA2194_03642	ZP_03755203.1	225377982	Roseburia
			inulinivorans
EUBREC_3075	YP_002938937.1	238925420	Eubacterium
			rectale
pct	CAB77207.1	7242549	Clostridium
			propionicum
NT01CX_2372	YP_878445.1	118444712	Clostridium
			novyi NT
Cbei_4543	YP_001311608.1	150019354	Clostridium
			beijerinckii
CBC_A0889	ZP_02621218.1	168186583	Clostridium
			botulinum
ygfH	NP_417395.1	16130821	Escherichia
			coli
CIT292_04485	ZP_03838384.1	227334728	Citrobacter
			youngae
SARI_04582	YP_001573497.1	161506385	Salmonella
			enterica
yinte0001_14430	ZP_04635364.1	238791727	Yersinia
			intermedia

The gene products of cat1, cat2, and cat3 of Clostridium kluyveri have been shown to exhibit succinyl-CoA, 4-hydroxybutyryl-CoA, and butyryl-CoA transferase activity, respectively (Seedorf et al., Proc. Natl. Acad. Sci U.S.A 105:2128-2133 (2008); Sohling et al., J Bacteriol. 178:871-880 (1996)). Similar CoA transferase activities are also present in Trichomonas vaginalis (van Grinsven et al., J. Biol. Chem. 283:1411-1418 (2008)) and Trypanosoma brucei (Riviere et al., J. Biol. Chem. 279:45337-45346 (2004)).


Protein	GenBank ID	GI Number	Organism

cat1	P38946.1	729048	Clostridium kluyveri
cat2	P38942.2	172046066	Clostridium kluyveri
cat3	EDK35586.1	146349050	Clostridium kluyveri
TVAG_395550	XP_001330176	123975034	Trichomonas
			vaginalis G3
Tb11.02.0290	XP_828352	71754875	Trypanosoma brucei

The glutaconyl-CoA-transferase (EC 2.8.3.12) enzyme from anaerobic bacterium Acidaminococcus fermentans reacts with glutaconyl-CoA and 3-butenoyl-CoA (Mack et al., 226:41-51 (1994)). The genes encoding this enzyme are gctA and gctB. This enzyme has reduced but detectable activity with other CoA derivatives including glutaryl-CoA, 2-hydroxyglutaryl-CoA, adipyl-CoA, crotonyl-CoA and acrylyl-CoA (Buckel et al., Eur. J Biochem. 118:315-321 (1981)). The enzyme has been cloned and expressed in E. coli (Mack et al., supra). Glutaconate CoA-transferase activity has also been detected in Clostridium sporosphaeroides and Clostridium symbiosum. Additional glutaconate CoA-transferase enzymes can be inferred by homology to the Acidaminococcus fermentans protein sequence.


Protein	GenBank ID	GI Number	Organism

gctA	CAA57199.1	559392	Acidaminococcus fermentans
gctB	CAA57200.1	559393	Acidaminococcus fermentans
gctA	ACJ24333.1	212292816	Clostridium symbiosum
gctB	ACJ24326.1	212292808	Clostridium symbiosum
gctA	NP_603109.1	19703547	Fusobacterium nucleatum
gctB	NP_603110.1	19703548	Fusobacterium nucleatum

A CoA transferase that can utilize acetyl-CoA as the CoA donor is acetoacetyl-CoA transferase, encoded by the E. coli atoA (alpha subunit) and atoD (beta subunit) genes (Korolev et al., Acta Crystallogr. D. Biol. Crystallogr. 58:2116-2121 (2002); Vanderwinkel et al., 33:902-908 (1968)). This enzyme has a broad substrate range (Sramek et al., Arch Biochem Biophys 171:14-26 (1975)) and has been shown to transfer the CoA moiety to acetate from a variety of branched and linear acyl-CoA substrates, including isobutyrate (Matthies et al., Appl Environ. Microbiol 58:1435-1439 (1992)), valerate (Vanderwinkel et al., Biochem. Biophys. Res. Commun. 33:902-908 (1968)) and butanoate (Vanderwinkel et al., Biochem. Biophys. Res. Commun. 33:902-908 (1968)). This enzyme is induced at the transcriptional level by acetoacetate, so modification of regulatory control may be necessary for engineering this enzyme into a pathway (Pauli et al., Eur. J Biochem. 29:553-562 (1972)). Similar enzymes exist in Corynebacterium glutamicum ATCC 13032 (Duncan et al., 68:5186-5190 (2002)), Clostridium acetobutylicum (Cary et al., Appl Environ Microbiol 56:1576-1583 (1990); Wiesenborn et al., Appl Environ Microbiol 55:323-329 (1989)), and Clostridium saccharoperbutylacetonicum (Kosaka et al., Biosci. Biotechnol Biochem. 71:58-68 (2007)).


Gene	GI number	GenBank ID	Organism

atoA	2492994	P76459.1	Escherichia coli
atoD	2492990	P76458.1	Escherichia coli
actA	62391407	YP_226809.1	Corynebacterium glutamicum
cg0592	62389399	YP_224801.1	Corynebacterium glutamicum
ctfA	15004866	NP_149326.1	Clostridium acetobutylicum
ctfB	15004867	NP_149327.1	Clostridium acetobutylicum
ctfA	31075384	AAP42564.1	Clostridium saccharoperbu-
			tylacetonicum
ctfB	31075385	AAP42565.1	Clostridium saccharoperbu-
			tylacetonicum

Beta-ketoadipyl-CoA transferase, also known as succinyl-CoA:3:oxoacid-CoA transferase, employs succinate as the CoA acceptor. This enzyme is encoded by pcaI and pcaJ in Pseudomonas putida (Kaschabek et al., J Bacteriol. 184:207-215 (2002)). Similar enzymes are found in Acinetobacter sp. ADP1 (Kowalchuk et al., Gene 146:23-30 (1994)), Streptomyces coelicolor and Pseudomonas knackmussii (formerly sp. B13) (Gobel et al., J Bacteriol. 184:216-223 (2002); Kaschabek et al., J Bacteriol. 184:207-215 (2002)). Additional exemplary succinyl-CoA:3:oxoacid-CoA transferases have been characterized in in Helicobacter pylori (Corthesy-Theulaz et al., J Biol. Chem. 272:25659-25667 (1997)), Bacillus subtilis (Stols et al., Protein Expr. Purif 53:396-403 (2007)) and Homo sapiens (Fukao, T., et al., Genomics 68:144-151 (2000); Tanaka, H., et al., Mol Hum Reprod 8:16-23 (2002)). Genbank information related to these genes is summarized below.


Gene	GI number	GenBank ID	Organism

pcaI	24985644	AAN69545.1	Pseudomonas putida
pcaJ	26990657	NP_746082.1	Pseudomonas putida
pcaI	50084858	YP_046368.1	Acinetobacter sp. ADP1
pcaJ	141776	AAC37147.1	Acinetobacter sp. ADP1
pcaI	21224997	NP_630776.1	Streptomyces coelicolor
pcaJ	21224996	NP_630775.1	Streptomyces coelicolor
catI	75404583	Q8VPF3	Pseudomonas
			knackmussii
catJ	75404582	Q8VPF2	Pseudomonas
			knackmussii
HPAG1_0676	108563101	YP_627417	Helicobacter pylori
HPAG1_0677	108563102	YP_627418	Helicobacter pylori
ScoA	16080950	NP_391778	Bacillus subtilis
ScoB	16080949	NP_391777	Bacillus subtilis
OXCT1	NP_000427	4557817	Homo sapiens
OXCT2	NP_071403	11545841	Homo sapiens

3.1.1.a Esterase/Lipase

Enzymes in the EC class 3.1.1 catalyze the hydrolysis and synthesis of ester bonds. Caprolactone hydrolase enzymes required for step G of FIG. 1 and step F of FIG. 2 are found in organisms that degrade cyclohexanone. The chnC gene product of Acinetobacter sp. NCIMB9871 was found to hydrolyze the ester bond of caprolactone, forming 6-hydroxyhexanote (Iwaki et al, AEM 65:5158-62 (1999)). Similar enzymes were identified in Arthrobacter sp. BP2 and Rhodococcus sp. Phi2 (Brzostowicz et al, AEM 69:334-42 (2003)).


Gene	GenBank ID	GI Number	Organism

chnC	BAC80218.1	33284998	Acinetobacter sp. NCIMB9871
chnC	AAN37478.1	27657619	Arthrobacter sp. BP2
chnC	AAN37490.1	27657632	Rhodococcus sp. Phi2

Formation of caprolactone may also be catalyzed by enzymes that catalyze the interconversion of cyclic lactones and open chain hydroxycarboxylic acids. The L-lactonase from Fusarium proliferatum ECU2002 exhibits lactonase and esterase activities on a variety of lactone substrates (Zhang et al., Appl. Microbiol. Biotechnol. 75:1087-1094 (2007)). The 1,4-lactone hydroxyacylhydrolase (EC 3.1.1.25), also known as 1,4-lactonase or gamma-lactonase, is specific for 1,4-lactones with 4-8 carbon atoms. The gamma lactonase in human blood and rat liver microsomes was purified (Fishbein et al., J Biol Chem 241:4835-4841 (1966)) and the lactonase activity was activated and stabilized by calcium ions (Fishbein et al., J Biol Chem 241:4842-4847 (1966)). The optimal lactonase activities were observed at pH 6.0, whereas high pH resulted in hydrolytic activities (Fishbein and Bessman, J Biol Chem 241:4842-4847 (1966)). Genes from Xanthomonas campestris, Aspergillus niger and Fusarium oxysporum have been annotated as 1,4-lactonase and can be utilized to catalyze the transformation of 4-hydroxybutyrate to GBL (Zhang et al., Appl Microbiol Biotechnol 75:1087-1094 (2007)).


Gene	Accession No.	GI No.	Organism

EU596535.1:	ACC61057.1	183238971	Fusarium
1 . . . 1206			proliferatum
xccb100_2516	YP_001903921.1	188991911	Xanthomonas
			campestris
An16g06620	CAK46996.1	134083519	Aspergillus
			niger
BAA34062	BAA34062.1	3810873	Fusarium
			oxysporum

Other enzyme candidates for converting 6-hydroxyhexanoate to caprolactone include lipases and esterases (or ester synthases). Lipases (EC 3.1.1.3) typically hydrolyze long-chain carboxylic acid esters, whereas esterases (EC 3.1.1.1) hydrolyze short-chain esters. The amidase from Brevibacterium sp. R312 (EC 3.5.1.4) is a likely enzyme with caprolactone-forming activity. This enzyme was shown to hydrolyze ethylacrylate (Thiery et al., J. Gen. Microbiol., 132:2205-8, 1986; Soubrier et al., Gene, 116:99-104, 1992). The microsomal epoxide hydrolase from Rattus norvegicus (EC 3.3.2.9) is another suitable enzyme (Guengerich et al., Rev. Biochem. Toxicol. 4:5-30, 1982). The protein sequences of these genes are provided below.


Gene	GenBank ID	GI Number	Organism

amiE	JC1174	98711	Brevibacterium sp.
Eph-1	P07687.1	123928	Rattus norvegicus

Additional ester synthase genes include the Acinetobacter sp. ADP1 atfA encoding a bifunctional enzyme with both wax ester synthase (WS) and acyl-CoA:diacylglycerol acyltransferase (DGAT) activities (Kalscheuer et al. A J Biol Chem 2003, 278: 8075-8082.); the Simmondsia chinensis gene AAD38041 encoding a enzyme required for the accumulation of waxes in jojoba seeds (Lardizabal et al. Plant Physiology 2000, 122: 645-655.); the Alcanivorax borkumensis atfA1 and atfA2 encoding bifunctional WS/DGAT enzymes (Kalscheuer et al. J Bacteriol 2007, 189: 918-928.); ths Fragaria×anananassa AAT encoding an alcohol acetyltransferasae (Noichinda et al. FoodSci Technol Res 1999, 5: 239-242.); the Rosa hybrid cultivar AA TI encoding an alcohol acetyltransferase (Guterman et al. Plant Mol Biol 2006, 60: 555-563.); and the Saccharomyces cerevisiae ATF1 and ATF2 encoding alcohol acetyltransferases (Mason et al. Yeast 2000, 16: 1287-1298.); and Ws1 and Ws2 from Marinobacter hydrocarbonoclasticus (Holtzapple, E. and Schmidt-Dannert, C., J. Bacteriol. 189 (10), 3804-3812, 2007). The carboxylesterase from Lactococcus lactis, encoded by estA, catalyzes the formation of esters from acetyl-CoA and alcohols such as ethanol and methanethiol (Nardi et al. J. Appl. Microbiol. 93:994-1002 (2002)). A thermostable carboxylesterase from Anoxybacillus sp. PDF1 was recently cloned and characterized (Ay et al, Prot Expr Purif 80:74-9 (2011)) but the sequence is not yet available. The alcohol O-acetyltransferase from Saccharomyces uvarum converts a wide range of alcohol substrates including branched-chain alcohols to their corresponding acetate esters (Yoshioka and Hashimoto, Agricul and Biol Chem, 45:2183-2191 (1981). The gene associated with this activity has not been identified to date. The protein sequences of the enzymes encoded by these genes are provided below.


Gene	GenBank ID	GI Number	Organism

atfA	Q8GGG1	81478805	Acinetobacter sp. ADP1
AF149919.1:	AAD38041	5020219	Simmondsia chinensis
13 . . . 1071
atfAl	YP694462	110835603	Alcanivorax borkumensis
			SK2
atfA2	YP693524	110834665	Alcanivora xborkumensis
			SK2
AAT	AAG13130.1	10121328	Fragaria × ananassa
AATl	Q5I6B5	75105208	Rosa hybrid cultivar
ATFl	P40353	2506980	Saccharomyces cerevisiae
ATF2	P53296	1723729	Saccharomyces cerevisiae
Ws2	ABO21021.1	126567232	Marinobacter
			hydrocarbonoclasticus
Ws1	ABO21020.1	126567230	Marinobacter
			hydrocarbonoclasticus
EstA	AAF62859.1	7453516	Lactococcus lactis

The Homo sapiens paraoxonase enzymes PON1, PON1 (G3C9), and PON3 (EC 3.1.8.1) possess both arylesterase and organophosphatase activities. PON1 has a common polymorphic site at residue 192, glutamine (R) or arginine (Q) which results in qualitative differences. For example, the R isozyme has a higher esterase activity than the S isozyme (Billecke et al., Drug Metab Dispos. 28:1335-1342 (2000)). In H. sapiens cells, PON1 resides on high-density lipoprotein (HDL) particles, and its activity and stability require this environment. Wild type and recombinant PON1 enzymes have been functionally expressed in other organisms (Rochu et al., Biochem. Soc. Trans. 35:1616-1620 (2007); Martin et al., Appl. Environ. Microbiol. (2009)). A directed evolution study of PON1 yielded several mutant enzymes with improved solubility and catalytic properties in E. coli (nucleotide accession numbers AY499188-AY499199) (Aharoni et al., Proc. Natl. Acad. Sci. U.S.A 101:482-487 (2004)). One recombinant variant from this study, G3C9 (Aharoni et al., Proc. Natl. Acad. Sci. U.S.A 101:482-487 (2004)), was recently used in an integrated bioprocess for the pH-dependent production of 4-valerolactone from levulinate (Martin et al., Appl. Environ. Microbiol. (2009)). Human PON3 is yet another suitable enzyme (Draganov et al., J. Lipid Res. 46:1239-1247 (2005)).


Gene	Accession No.	GI No.	Organism

PON1	NP_000437.3	19923106	Homo sapiens
PON1 (G3C9)	AAR95986.1	40850544	Synthetic variant
PON3	NP_000931.1	29788996	Homo sapiens

Additional ester synthase candidates include the Candida antarctica lipase B (Efe et al., Biotechnol. Bioeng. 99:1392-1406 (2008)) and EstF1 from Pseudomonas fluorescens, encoded by EstF1 (Khalameyzer et al., Appl. Environ. Microbiol. 65:477-482 (1999)). Other lipase enzymes from organisms such as Pseudomonas fluorescens and Bacillus subtilis may also catalyze this transformation. The B. subtilis and P. fluorescens genes encode triacylglycerol lipase enzymes which have been cloned and characterized in E. coli (Dartois et al., Biochim. Biophys. Acta 1131:253-260 (1992); Tan et al., Appl. Environ. Microbiol. 58:1402-1407 (1992)).


Gene	Accession No.	GI No.	Organism

calB	P41365.1	1170790	Candida antarctica
EstF1	AAC36352.1	3641341	Pseudomonas fluorescens
lipB	P41773.1	1170792	Pseudomonas fluorescens
estA	P37957.1	7676155	Bacillus subtilis

3.1.2.a CoA Hydrolase

Enzymes in the 3.1.2 family hydrolyze acyl-CoA molecules to their corresponding acids. Such an enzyme is depicted in Step F of FIG. 1 and Step B of FIG. 5. Several CoA hydrolases have been demonstrated to hydrolyze adipyl-CoA, or alternately accept a broad range of substrates. For example, the enzyme encoded by acot12 from Rattus norvegicus brain (Robinson et al., Biochem. Biophys. Res. Commun. 71:959-965 (1976)) can react with butyryl-CoA, hexanoyl-CoA and malonyl-CoA. The human dicarboxylic acid thioesterase, encoded by acot8, exhibits activity on glutaryl-CoA, adipyl-CoA, suberyl-CoA, sebacyl-CoA, and dodecanedioyl-CoA (Westin et al., J. Biol. Chem. 280:38125-38132 (2005)). The closest E. coli homolog to this enzyme, tesB, can also hydrolyze a range of CoA thiolesters (Naggert et al., J Biol Chem 266:11044-11050 (1991)). A similar enzyme has also been characterized in the rat liver (Deana R., Biochem Int 26:767-773 (1992)). Additional enzymes with hydrolase activity in E. coli include ybgC, paaI, and ybdB (Kuznetsova, et al., FEMS Microbiol Rev, 2005, 29(2):263-279; Song et al., J Biol Chem, 2006, 281(16):11028-38). Though its sequence has not been reported, the enzyme from the mitochondrion of the pea leaf has a broad substrate specificity, with demonstrated activity on acetyl-CoA, propionyl-CoA, butyryl-CoA, palmitoyl-CoA, oleoyl-CoA, succinyl-CoA, and crotonyl-CoA (Zeiher et al., Plant. Physiol. 94:20-27 (1990)) The acetyl-CoA hydrolase, ACH1, from S. cerevisiae represents another candidate hydrolase (Buu et al., J. Biol. Chem. 278:17203-17209 (2003)).


Gene name	GenBank ID	GI number	Organism

acot12	NP_570103.1	18543355	Rattus norvegicus
tesB	NP_414986	16128437	Escherichia coli
acot8	CAA15502	3191970	Homo sapiens
acot8	NP_570112	51036669	Rattus norvegicus
tesA	NP_415027	16128478	Escherichia coli
ybgC	NP_415264	16128711	Escherichia coli
paaI	NP_415914	16129357	Escherichia coli
ybdB	NP_415129	16128580	Escherichia coli
ACH1	NP_009538	6319456	Saccharomyces cerevisiae

Yet another candidate hydrolase is the glutaconate CoA-transferase from Acidaminococcus fermentans. This enzyme was transformed by site-directed mutagenesis into an acyl-CoA hydrolase with activity on glutaryl-CoA, acetyl-CoA and 3-butenoyl-CoA (Mack et al., FEBS. Lett. 405:209-212 (1997)). This suggests that the enzymes encoding succinyl-CoA:3-ketoacid-CoA transferases and acetoacetyl-CoA:acetyl-CoA transferases may also serve as candidates for this reaction step but would require certain mutations to change their function.


Gene name	GenBank ID	GI number	Organism

gctA	CAA57199	559392	Acidaminococcus fermentans
gctB	CAA57200	559393	Acidaminococcus fermentans

Another CoA hydrolase enzyme is 3-hydroxyisobutyryl-CoA hydrolase which has been described to efficiently catalyze the conversion of 3-hydroxyisobutyryl-CoA to 3-hydroxyisobutyrate during valine degradation (Shimomura et al., J Biol Chem. 269:14248-14253 (1994)). Genes encoding this enzyme include hibch of Rattus norvegicus (Shimomura et al., Methods Enzymol. 324:229-240 (2000)) and Homo sapiens (Shimomura et al., supra). Similar gene candidates can also be identified by sequence homology, including hibch of Saccharomyces cerevisiae and BC_2292 of Bacillus cereus.


Gene name	GenBank ID	GI number	Organism

hibch	Q5XIE6.2	146324906	Rattus norvegicus
hibch	Q6NVY1.2	146324905	Homo sapiens
hibch	P28817.2	2506374	Saccharomyces cerevisiae
BC_2292	AP09256	29895975	Bacillus cereus

3.7.1.a Hydrolase

Cyclohexane-1,2-dione hydrolase is a thiamin-diphosphate and FAD-dependent enzyme (EC 3.7.1.11) catalyzing the conversion of cyclohexane-1,2-dione to adipate semialdehyde. This enzyme has been characterized in Azoarcus sp. strain 22Lin, where it participates in cyclohexane-1,2-diol degradation (Steinbeck et al, J Bacteriol, in press (2011); Harder, J., Arch. Microbiol. 168:199-203 (1997)). The enzyme also oxidizes adipate semialdehyde to adipate. A similar transformation is catalyzed in the myo-inositol degradation pathway of organisms such as Bacillus subtilis, in which the cyclic dione 2,3-diketo-4-deoxy-epi-inositol is hydrolyzed to a linear product, 5-dehydro-2-deoxy-D-gluconate, by a diketodeoxyinositol hydrolase (EC 3.7.1.-). A partially purified protein catalyzing this reaction has been studied in Klebsiella aerogenes (Berman et al., J. Biol. Chem. 241:800-806 (1966)). A gene has not been associated with this activity to date. The CDH from Azoarcus sp. strain 22Lin and close homologs are shown in the table below.


Protein	GenBank ID	GI Number	Organism

cdh	P0CH62.1	306755656	Azoarcus sp.
			Strain 22Lin
Ahas	ZP_04823388.1	251780468	Clostridium botulinum
ilvB2	ZP_06013676.1	262040433	Klebsiella pneumoniae
			subsp.
			rhinoscleromatis
Deba_0336	YP_003806306.1	302341777	Desulfarculus baarsii
			DSM 2075
ilvB	AEN91169.1	345446152	Bacillus megaterium
			WSH-002

The formation of 2-ketocyclohexane-1-carboxoyl-CoA from pimeloyl-CoA (Step A of FIG. 5) is catalyzed by an enzyme with 2-ketocyclohexane-1-carboxoyl-CoA hydrolase activity. This enzymatic activity has been indicated to occur in the ring-closing direction in Syntrophus aciditrophicus during growth on crotonate (Mouttaki et al., Appl. Environ. Micobiol. 73:930-938 (2007)). This activity was also demonstrated in cell-free extracts of S. aciditrophicus in co-culture with another microbe during growth on benzoate (Elshahed et al., Appl. Environ. Microbiol. 67:1728-1738 (2001)). An enzyme catalyzing this activity in the ring-opening direction has been characterized in Rhodopseudomonas palustris, where it is encoded by badI (Pelletier et al., J. Bacteriol. 180:2330-2336 (1998)). The R. palustris enzyme has been expressed in E. coli where it was assayed for enzymatic activity in the ring-opening direction; however, such activity was not observed (Egland et al., Proc. Natl. Acad. Sci U.S.A. 94:6484-6489 (1997)). Several genes in the S. aciditrophicus genome bear sequence homology to the badI gene of R. palustris (McInerney et al., Proc. Natl Acad. Sci U.S. A. 104:7600-7605 (2007)), including syn 01653 (38%), syn 03076 (33%), syn_02400 (33%), syn_03076 (30%) and syn_01309 (31%).


Protein	GenBank ID	GI Number	Organism

badI	NP_946006.1	39933730	Rhodopseudomonas
			palustris
syn_01653	YP_463074.1	85860872	Syntrophus aciditrophicus
syn_01654	YP_463073.1	85860871	Syntrophus aciditrophicus
syn_02400	YP_462924.1	85860722	Syntrophus aciditrophicus
syn_03076	YP_463118.1	85860916	Syntrophus aciditrophicus
syn_01309	YP_461962.1	85859760	Syntrophus aciditrophicus

Another suitable enzyme candidate for Step A of FIG. 5 is napthoyl-CoA synthetase (EC 4.1.3.36), an enzyme participating in menaquinone biosynthesis. This enzyme catalyzes the ring-closing conversion of succinyl-benzoyl-CoA to 1,4-dihydroxy-2-napthoyl-CoA. The badI gene product of R. palustris shares as much as 53% sequence identity with 1,4-dihydroxynapthoyl-CoA synthetase homologs in other organisms (Eberhard et al., J. Am. Chem. Soc. 126:7188-7189 (2004)), and enzymes catalyzing this transformation can demonstrate 2-ketocyclohexane-1-carboxyl-CoA hydrolase activity in the ring-closing direction. Such enzymes are found in Escherichia coli (Sharma et al., J. Bacteriol. 174:5057-5062 (1992)), Bacillus subtilis (Driscoll et al., J. Batceriol. 174:5063-5071 (1992)), Staphylococcus aureus (Ulaganathan et al., Acta Crstyallogr. Sect. F. Struct. Biol. Cyst. Commun. 63:908-913 (2007)) and Geobacillus kaustophilus (Kanajunia et al., Acta Crstyallogr. Sect. F. Struct. Biol. Cyst. Commun. 63:103-105 (2007)). Additionally, structural data is available for the enzymes from Mycobacterium tuberculosis (Johnston et al., Acta Crstyallogr. D. Biol. Crystallogr. 61:1199-1206 (2005)), S. aureus (Ulaganathan et al., supra) and Geobacillus kaustophilus (Kanaujia et al., supra).


Protein	GenBank ID	GI Number	Organism

menB	AAC75322	1788597	Escherichia coli K12 sp. MG1655
menB	AAC37016	143186	Bacillus subtilis
menB	NP_215062	15607688	Mycobacterium tuberculosis
menB	BAB57207	14246815	Staphylococcus aureus
menB	BAD77158	56381250	Geobacillus kaustophilus

4.1.1.a Decarboxylase

A decarboxylase enzyme suitable for decarboxylating 2-ketocyclohexane-1-carboxylate (step C of FIG. 5) is the 3-ketoacid decarboxylase, acetoacetate decarboxylase (EC 4.1.1.4). The enzyme from Clostridium acetobutylicum, encoded by adc, has a broad substrate specificity and has been shown to decarboxylate numerous alternate substrates including 2-ketocyclohexane carboxylate, 3-oxopentanoate, 2-oxo-3-phenylpropionic acid, 2-methyl-3-oxobutyrate and benzoyl-acetate (Rozzel et al., J. Am. Chem. Soc. 106:4937-4941 (1984); Benner and Rozzell, J. Am. Chem. Soc. 103:993-994 (1981); Autor et al., J Biol. Chem. 245:5214-5222 (1970)). An acetoacetate decarboxylase has also been characterized in Clostridium beijerinckii (Ravagnani et al., Mol. Microbiol 37:1172-1185 (2000)). The acetoacetate decarboxylase from Bacillus polymyxa, characterized in cell-free extracts, also has a broad substrate specificity for 3-keto acids and can decarboxylate 3-oxopentanoate (Matiasek et al., Curr. Microbiol 42:276-281 (2001)). The gene encoding this enzyme has not been identified to date and the genome sequence of B. polymyxa is not yet available. Another adc is found in Clostridium saccharoperbutylacetonicum (Kosaka, et al., Biosci. Biotechnol Biochem. 71:58-68 (2007)). Gene candidates in other organisms, including Clostridium botulinum and Bacillus amyloliquefaciens, can be identified by sequence homology.


Protein	GenBank ID	GI Number	Organism

adc	NP_149328.1	15004868	Clostridium
			acetobutylicum
adc	AAP42566.1	31075386	Clostridium
			saccharoperbu-
			tylacetonicum
adc	YP_001310906.1	150018652	Clostridium
			beijerinckii
CLL_A2135	YP_001886324.1	187933144	Clostridium
			botulinum
RBAM_030030	YP_001422565.1	154687404	Bacillus
			amyloliquefaciens

4.2.1.a Hydro-Lyase

Several transformations involving the removal of water are depicted in FIGS. 2 and 4. In Step C of FIG. 2, the dehydration of 3,6-dihydroxyhexanoyl-CoA to 6-hydroxyhex-2-enoyl-CoA is catalyzed by a 3-hydroxyacyl-CoA dehydratase. In FIG. 4, the conversion of cyclohexane-1,2-diol to cyclohexanone (Step D) is catalyzed by a diol dehydratase in EC class 4.2.1. Several relevant dehydratase enzymes have been described in the literature and represent suitable candidates for these steps.
A 3-hydroxyacyl-CoA dehydratase is required for step C of FIG. 2. Enoyl-CoA hydratases (EC 4.2.1.17) catalyze the dehydration of a range of 3-hydroxyacyl-CoA substrates (Roberts et al., Arch. Microbiol 117:99-108 (1978); Agnihotri et al., Bioorg. Med. Chem. 11:9-20 (2003); Conrad et al., J Bacteriol. 118:103-111 (1974)). The enoyl-CoA hydratase of Pseudomonas putida, encoded by ech, catalyzes the conversion of 3-hydroxybutyryl-CoA to crotonyl-CoA (Roberts et al., Arch. Microbiol 117:99-108 (1978)). This transformation is also catalyzed by the crt gene product of Clostridium acetobutylicum, the crt1 gene product of C. kluyveri, and other clostridial organisms Atsumi et al., Metab Eng 10:305-311 (2008); Boynton et al., J Bacteriol. 178:3015-3024 (1996); Hillmer et al., FEBS Lett. 21:351-354 (1972)). Additional enoyl-CoA hydratase candidates are phaA and phaB, of P. putida, and paaA and paaB from P. fluorescens (Olivera et al., Proc. Natl. Acad. Sci U.S.A 95:6419-6424 (1998)). The gene product of pimF in Rhodopseudomonas palustris is predicted to encode an enoyl-CoA hydratase that participates in pimeloyl-CoA degradation (Harrison et al., Microbiology 151:727-736 (2005)). Lastly, a number of Escherichia coli genes have been shown to demonstrate enoyl-CoA hydratase functionality including maoC (Park et al., J Bacteriol. 185:5391-5397 (2003)), paaF (Ismail et al., Eur. J Biochem. 270:3047-3054 (2003); Park et al., Appl. Biochem. Biotechnol 113-116:335-346 (2004); Park et al., Biotechnol Bioeng 86:681-686 (2004)) and paaG (Ismail et al., Eur. J Biochem. 270:3047-3054 (2003); Park and Lee, Appl. Biochem. Biotechnol 113-116:335-346 (2004); Park and Yup, Biotechnol Bioeng 86:681-686 (2004)).


Gene	GenBank ID	GI number	Organism

ech	NP_745498.1	26990073	Pseudomonas putida
crt	NP_349318.1	15895969	Clostridium acetobutylicum
crt1	YP_001393856	153953091	Clostridium kluyveri
phaA	ABF82233.1	26990002	Pseudomonas putida
phaB	ABF82234.1	26990001	Pseudomonas putida
paaA	NP_745427.1	106636093	Pseudomonas fluorescens
paaB	NP_745426.1	106636094	Pseudomonas fluorescens
maoC	NP_415905.1	16129348	Escherichia coli
paaF	NP_415911.1	16129354	Escherichia coli
paaG	NP_415912.1	16129355	Escherichia coli

Alternatively, the E. coli gene products of fadA and fadB encode a multienzyme complex involved in fatty acid oxidation that exhibits enoyl-CoA hydratase activity (Yang et al., Biochemistry 30:6788-6795 (1991); Yang, J Bacteriol. 173:7405-7406 (1991); Nakahigashi et al., Nucleic Acids Res. 18:4937 (1990)). Knocking out a negative regulator encoded by fadR can be utilized to activate the fadB gene product (Sato et al., J Biosci. Bioeng 103:38-44 (2007)). The fadI and fad genes encode similar functions and are naturally expressed under anaerobic conditions (Campbell et al., Mol. Microbiol 47:793-805 (2003)).


Protein	GenBank ID	GI Number	Organism

fadA	YP_026272.1	49176430	Escherichia coli
fadB	NP_418288.1	16131692	Escherichia coli
fadI	NP_416844.1	16130275	Escherichia coli
fadJ	NP_416843.1	16130274	Escherichia coli
fadR	NP_415705.1	16129150	Escherichia coli

Diol dehydratase enzymes suitable for converting cyclohexane-1,2-diol to cyclohexanone include dihydroxy-acid dehydratase (EC 4.2.1.9), propanediol dehydratase (EC 4.2.1.28), glycerol dehydratase (EC 4.2.1.30) and myo-inositose dehydratase (EC 4.2.1.44).
Adenosylcobalamin-dependent diol dehydratases contain alpha, beta and gamma subunits, which are all required for enzyme function. Exemplary propanediol dehydratase candidates are found in Klebsiella pneumoniae (Toraya et al., Biochem. Biophys. Res. Commun. 69:475-480 (1976); Tobimatsu et al., Biosci. Biotechnol Biochem. 62:1774-1777 (1998)), Salmonella typhimurium (Bobik et al., J Bacteriol. 179:6633-6639 (1997)), Klebsiella oxytoca (Tobimatsu et al., J Biol. Chem. 270:7142-7148 (1995)) and Lactobacillus collinoides (Sauvageot et al., FEMS Microbiol Lett. 209:69-74 (2002)). Methods for isolating diol dehydratase gene candidates in other organisms are well known in the art (e.g. U.S. Pat. No. 5,686,276).


Protein	GenBank ID	GI Number	Organism

pddC	AAC98386.1	4063704	Klebsiella pneumoniae
pddB	AAC98385.1	4063703	Klebsiella pneumoniae
pddA	AAC98384.1	4063702	Klebsiella pneumoniae
pduC	AAB84102.1	2587029	Salmonella typhimurium
pduD	AAB84103.1	2587030	Salmonella typhimurium
pduE	AAB84104.1	2587031	Salmonella typhimurium
pddA	BAA08099.1	868006	Klebsiella oxytoca
pddB	BAA08100.1	868007	Klebsiella oxytoca
pddC	BAA08101.1	868008	Klebsiella oxytoca
pduC	CAC82541.1	18857678	Lactobacillus collinoides
pduD	CAC82542.1	18857679	Lactobacillus collinoides
pduE	CAD01091.1	18857680	Lactobacillus collinoides

Enzymes in the glycerol dehydratase family (EC 4.2.1.30) are also diol dehydratases. Exemplary gene candidates are encoded by gldABC and dhaB123 in Klebsiella pneumoniae (World Patent WO 2008/137403) and (Toraya et al., Biochem. Biophys. Res. Commun. 69:475-480 (1976)), dhaBCE in Clostridium pasteuranum (Macis et al., FEMS Microbiol Lett. 164:21-28 (1998)) and dhaBCE in Citrobacter freundii (Seyfried et al., J Bacteriol. 178:5793-5796 (1996)). Variants of the B12-dependent diol dehydratase from K. pneumoniae with 80- to 336-fold enhanced activity were recently engineered by introducing mutations in two residues of the beta subunit (Qi et al., J. Biotechnol. 144:43-50 (2009)). Diol dehydratase enzymes with reduced inactivation kinetics were developed by DuPont using error-prone PCR (WO 2004/056963).


Protein	GenBank ID	GI Number	Organism

gldA	AAB96343.1	1778022	Klebsiella pneumoniae
gldB	AAB96344.1	1778023	Klebsiella pneumoniae
gldC	AAB96345.1	1778024	Klebsiella pneumoniae
dhaB1	ABR78884.1	150956854	Klebsiella pneumoniae
dhaB2	ABR78883.1	150956853	Klebsiella pneumoniae
dhaB3	ABR78882.1	150956852	Klebsiella pneumoniae
dhaB	AAC27922.1	3360389	Clostridium pasteuranum
dhaC	AAC27923.1	3360390	Clostridium pasteuranum
dhaE	AAC27924.1	3360391	Clostridium pasteuranum
dhaB	P45514.1	1169287	Citrobacter freundii
dhaC	AAB48851.1	1229154	Citrobacter freundii
dhaE	AAB48852.1	1229155	Citrobacter freundii

If a B12-dependent diol dehydratase is utilized, heterologous expression of the corresponding reactivating factor is recommended. B12-dependent diol dehydratases are subject to mechanism-based suicide activation by substrates and some downstream products. Inactivation, caused by a tight association with inactive cobalamin, can be partially overcome by diol dehydratase reactivating factors in an ATP-dependent process. Regeneration of the B12 cofactor requires an additional ATP. Diol dehydratase regenerating factors are two-subunit proteins. Exemplary candidates are found in Klebsiella oxytoca (Mori et al., J Biol. Chem. 272:32034-32041 (1997)), Salmonella typhimurium (Bobik et al., J Bacteriol. 179:6633-6639 (1997); Chen et al., J Bacteriol. 176:5474-5482 (1994)), Lactobacillus collinoides (Sauvageot et al., FEMS Microbiol Lett. 209:69-74 (2002)), Klebsiella pneumonia (World Patent WO 2008/137403).


Protein	GenBank ID	GI Number	Organism

ddrA	AAC15871	3115376	Klebsiella oxytoca
ddrB	AAC15872	3115377	Klebsiella oxytoca
pduG	AAB84105	16420573	Salmonella typhimurium
pduH	AAD39008	16420574	Salmonella typhimurium
pduG	YP_002236779	206579698	Klebsiella pneumoniae
pduH	YP_002236778	206579863	Klebsiella pneumoniae
pduG	CAD01092	29335724	Lactobacillus collinoides
pduH	AJ297723	29335725	Lactobacillus collinoides

B12-independent diol dehydratase enzymes are glycyl radicals that utilize S-adenosylmethionine (SAM) as a cofactor and function under strictly anaerobic conditions. The glycerol dehydrogenase and corresponding activating factor of Clostridium butyricum, encoded by dhaB1 and dhaB2, have been well-characterized (O'Brien et al., Biochemistry 43:4635-4645 (2004); Raynaud et al., Proc. Natl. Acad. Sci U.S.A 100:5010-5015 (2003)). This enzyme was recently employed in a 1,3-propanediol overproducing strain of E. coli and was able to achieve very high titers of product (Tang et al., Appl. Environ. Microbiol. 75:1628-1634 (2009)). An additional B12-independent diol dehydratase enzyme and activating factor from Roseburia inulinivorans was shown to catalyze the conversion of 2,3-butanediol to 2-butanone (US 2009/09155870).


Protein	GenBank ID	GI Number	Organism

dhaB1	AAM54728.1	27461255	Clostridium butyricum
dhaB2	AAM54729.1	27461256	Clostridium butyricum
rdhtA	ABC25539.1	83596382	Roseburia inulinivorans
rdhtB	ABC25540.1	83596383	Roseburia inulinivorans

Dihydroxy-acid dehydratase (DHAD, EC 4.2.1.9) is a B12-independent enzyme participating in branched-chain amino acid biosynthesis. In its native role, it converts 2,3-dihydroxy-3-methylvalerate to 2-keto-3-methyl-valerate, a precursor of isoleucine. In valine biosynthesis the enzyme catalyzes the dehydration of 2,3-dihydroxy-isovalerate to 2-oxoisovalerate. The DHAD from Sulfolobus solfataricus has a broad substrate range and activity of a recombinant enzyme expressed in E. coli was demonstrated on a variety of aldonic acids (KIM et al., J. Biochem. 139:591-596 (2006)). The S. solfataricus enzyme is tolerant of oxygen unlike many diol dehydratase enzymes. The E. coli enzyme, encoded by ilvD, is sensitive to oxygen, which inactivates its iron-sulfur cluster (Flint et al., J. Biol. Chem. 268:14732-14742 (1993)). Similar enzymes have been characterized in Neurospora crassa (Altmiller et al., Arch. Biochem. Biophys. 138:160-170 (1970)) and Salmonella typhimurium (Armstrong et al., Biochim. Biophys. Acta 498:282-293 (1977)). Other groups have shown that the overexpression of one or more Aft proteins or homologs thereof improves DHAD activity (US Patent Application 2011/0183393. In Saccharomyces cerevisiae, the Aft1 and Aft2 proteins are transcriptional activators that regulate numerous proteins related to the acquisition, compartmentalization, and utilization of iron.


Protein	GenBank ID	GI Number	Organism

ilvD	NP_344419.1	15899814	Sulfolobus solfataricus
ilvD	AAT48208.1	48994964	Escherichia coli
ilvD	NP_462795.1	16767180	Salmonella typhimurium
ilvD	XP_958280.1	85090149	Neurospora crassa
Aft1	P22149.2	1168370	Saccharomyces cerevisiae
Aft2	Q08957.1	74583775	Saccharomyces cerevisiae

The diol dehydratase myo-inosose-2-dehydratase (EC 4.2.1.44) is another exemplary candidate. Myo-inosose is a six-membered ring containing adjacent alcohol groups. A purified enzyme encoding myo-inosose-2-dehydratase functionality has been studied in Klebsiella aerogenes in the context of myo-inositol degradation (Berman et al., J Biol. Chem. 241:800-806 (1966)), but has not been associated with a gene to date. The myo-inosose-2-dehydratase of Sinorhizobium fredii was cloned and functionally expressed in E. coli (Yoshida et al., Biosci. Biotechnol. Biochem. 70:2957-2964 (2006)). A similar enzyme from B. subtilis, encoded by iolE, has also been studied (Yoshida et al., Microbiology 150:571-580 (2004)).


Protein	GenBank ID	GI Number	Organism

iolE	P42416.1	1176989	Bacillus subtilis
iolE	AAX24114.1	60549621	Sinorhizobium fredii

6.2.1.a CoA Synthetase

The conversion of acyl-CoA substrates to their acid products can be catalyzed by a CoA acid-thiol ligase or CoA synthetase in the 6.2.1 family of enzymes. Several transformations require a CoA synthetase to interconvert carboxylic acids and their corresponding acyl-CoA derivatives, including steps C and F of FIG. 1, step E of FIG. 2 and step B of FIG. 5. Enzymes catalyzing these exact transformations have not been characterized to date; however, several enzymes with broad substrate specificities have been described in the literature.
ADP-forming acetyl-CoA synthetase (ACD, EC 6.2.1.13) is an enzyme that couples the conversion of acyl-CoA esters to their corresponding acids with the concomitant synthesis of ATP. ACD I from Archaeoglobus fulgidus, encoded by AF1211, was shown to operate on a variety of linear and branched-chain substrates including isobutyrate, isopentanoate, and fumarate (Musfeldt et al., J Bacteriol. 184:636-644 (2002)). A second reversible ACD in Archaeoglobus fulgidus, encoded by AF 1983, was also shown to have a broad substrate range with high activity on cyclic compounds phenylacetate and indoleacetate (Musfeldt and Schonheit, J Bacteriol. 184:636-644 (2002)). The enzyme from Haloarcula marismortui (annotated as a succinyl-CoA synthetase) accepts propionate, butyrate, and branched-chain acids (isovalerate and isobutyrate) as substrates, and was shown to operate in the forward and reverse directions (Brasen et al., Arch Microbiol 182:277-287 (2004)). The ACD encoded by PAE3250 from hyperthermophilic crenarchaeon Pyrobaculum aerophilum showed the broadest substrate range of all characterized ACDs, reacting with acetyl-CoA, isobutyryl-CoA (preferred substrate) and phenylacetyl-CoA (Brasen et al, supra). Directed evolution or engineering can be used to modify this enzyme to operate at the physiological temperature of the host organism. The enzymes from A. fulgidus, H. marismortui and P. aerophilum have all been cloned, functionally expressed, and characterized in E. coli (Brasen and Schonheit, supra; Musfeldt and Schonheit, J Bacteriol. 184:636-644 (2002)). An additional candidate is succinyl-CoA synthetase, encoded by sucCD of E. coli and LSC1 and LSC2 genes of Saccharomyces cerevisiae. These enzymes catalyze the formation of succinyl-CoA from succinate with the concomitant consumption of one ATP in a reaction which is reversible in vivo (Buck et al., Biochemistry 24:6245-6252 (1985)). The acyl CoA ligase from Pseudomonas putida has been demonstrated to work on several aliphatic substrates including acetic, propionic, butyric, valeric, hexanoic, heptanoic, and octanoic acids and on aromatic compounds such as phenylacetic and phenoxyacetic acids (Fernandez-Valverde et al., Appl. Environ. Microbiol. 59:1149-1154 (1993)). A related enzyme, malonyl CoA synthetase (6.3.4.9) from Rhizobium leguminosarum could convert several diacids, namely, ethyl-, propyl-, allyl-, isopropyl-, dimethyl-, cyclopropyl-, cyclopropylmethylene-, cyclobutyl-, and benzyl-malonate into their corresponding monothioesters (Pohl et al., J. Am. Chem. Soc. 123:5822-5823 (2001)).


Protein	GenBank ID	GI Number	Organism

AF1211	NP_070039.1	11498810	Archaeoglobus fulgidus
AF1983	NP_070807.1	11499565	Archaeoglobus fulgidus
scs	YP_135572.1	55377722	Haloarcula marismortui
PAE3250	NP_560604.1	18313937	Pyrobaculum aerophilum str.
			IM2
sucC	NP_415256.1	16128703	Escherichia coli
sucD	AAC73823.1	1786949	Escherichia coli
LSC1	NP_014785	6324716	Saccharomyces cerevisiae
LSC2	NP_011760	6321683	Saccharomyces cerevisiae
paaF	AAC24333.2	22711873	Pseudomonas putida
matB	AAC83455.1	3982573	Rhizobium leguminosarum

Another candidate enzyme is 6-carboxyhexanoate-CoA ligase, also known as pimeloyl-CoA ligase (EC 6.2.1.14), which naturally activates pimelate to pimeloyl-CoA during biotin biosynthesis in gram-positive bacteria. The enzyme from Pseudomonas mendocina, cloned into E. coli, was shown to accept the alternate substrates hexanedioate and nonanedioate (Binieda et al., Biochem. J 340 (Pt 3):793-801 (1999)). Other candidates are found in Bacillus subtilis (Bower et al., J Bacteriol. 178:4122-4130 (1996)) and Lysinibacillus sphaericus (formerly Bacillus sphaericus) (Ploux et al., Biochem. J 287 (Pt 3):685-690 (1992)).


Protein	GenBank ID	GI Number	Organism

bioW	NP_390902.2	50812281	Bacillus subtilis
bioW	CAA10043.1	3850837	Pseudomonas mendocina
bioW	P22822.1	115012	Bacillus sphaericus

Additional CoA-ligases include the rat dicarboxylate-CoA ligase for which the sequence is yet uncharacterized (Vamecq et al., Biochem. J 230:683-693 (1985)), either of the two characterized phenylacetate-CoA ligases from P. chrysogenum (Lamas-Maceiras et al., Biochem. J 395:147-155 (2006); Wang et al., 360:453-458 (2007)), the phenylacetate-CoA ligase from Pseudomonas putida (Martinez-Blanco et al., J Biol Chem 265:7084-7090 (1990)) and the 6-carboxyhexanoate-CoA ligase from Bacillus subtilis (Bower et al. J Bacteriol 178(14):4122-4130 (1996)). Acetoacetyl-CoA synthetases from Mus musculus (Hasegawa et al., Biochim Biophys Acta 1779:414-419 (2008)) and Homo sapiens (Ohgami et al., Biochem. Pharmacol. 65:989-994 (2003)) naturally catalyze the ATP-dependent conversion of acetoacetate into acetoacetyl-CoA.


Gene	Accession No.	GI No.	Organism

phl	CAJ15517.1	77019264	Penicillium chrysogenum
phlB	ABS19624.1	152002983	Penicillium chrysogenum
paaF	AAC24333.2	22711873	Pseudomonas putida
bioW	NP_390902.2	50812281	Bacillus subtilis
AACS	NP_084486.1	21313520	Mus musculus
AACS	NP_076417.2	31982927	Homo sapiens

No EC

Formation of caprolactone from 6-hydroxyhexanoyl-CoA (step D of FIG. 1 and step F of FIG. 2) either occurs spontaneously or is catalyzed by enzymes having 6-hydroxyhexanoyl-CoA cyclase or alcohol transferase activity. Several enzymes with alcohol transferase activity were demonstrated in Examples 1-10 of U.S. Pat. No. 7,901,915. These include Novozyme 435 (immobilized lipase B from Candida antarctica, Sigma), Lipase C2 from Candida cylindracea (Alphamerix Ltd), lipase from Pseudomonas fluorescens (Alphamerix Ltd), L-aminoacylase ex Aspergillus spp., and protease ex Aspergillus oryzae. Such enzymes were shown to form methyl acrylate and ethyl acrylate from acrylyl-CoA and methanol or ethanol, respectively. Similar alcohol transferase enzymes can also be used to form cyclic esters such as caprolactone. Other suitable candidates include esterase enzymes in EC class 3.1.1, described above. Additional candidates include O-acyltransferases that transfer acyl groups from acyl-CoA to alcohols. Suitable O-acyltransferases include serine O-acetyltransferase (EC 2.3.1.30) such as cysE of E. coli, homoserine O-acetyltransferase (EC 2.3.1.31) enzymes such as met2 of Saccharomyces cerevisiae, or carnitine O-acyltransferases (EC 2.3.1.21) such as Cpt1a of Rattus norvegicus (Langin et al Gene 49:283-93 (1986); Denk et al, J Gen Microbiol 133:515-25 (1987); de Vries et al, Biochem 36:5285-92 (1997)).


Gene	Accession No.	GI No.	Organism

Met2	NP_014122.1	6324052	Saccharomyces cerevisiae
cysE	NP_418064.1	16131478	Escherichia coli
Cpt1a	NP_113747.2	162287173	Rattus norvegicus

Cyclization of 6-hydroxyhexanoyl-phosphate to caprolactone (Step I of FIGS. 1 and 2) can either occur spontaneously or by an enzyme with 6-hydroxyhexanoyl phosphate cyclase activity. An exemplary enzyme for this transformation is acyl-phosphate:glycerol-3-phosphate acyltransferase, encoded by plsY of Streptococcus pneumoniae (Lu et al, J Biol Chem 282:11339-46 (2007)). Although this enzyme catalyzes an intermolecular reaction, it could also catalyze the intramolecular ester-forming reaction to caprolactone. Genes encoding similar enzymes are listed in the table below. Alcohol transferase enzymes and esterase enzymes described above are also suitable candidates.


Gene	Accession No.	GI No.	Organism

plsY	P0A4P9.1	61250558	Streptococcus pneumoniae
plsY	YP_001035186.1	125718053	Streptococcus sanguinis
ykaC	NP_267134.1	15672960	Lactococcus lactis
plsY	NP_721591.1	24379636	Streptococcus mucans

Example II

Exemplary Hydrogenase and CO Dehydrogenase Enzymes for Extracting Reducing Equivalents from Syngas and Exemplary Reductive TCA Cycle Enzymes

Enzymes of the reductive TCA cycle useful in the non-naturally occurring microbial organisms of the present invention include one or more of ATP-citrate lyase and three CO₂-fixing enzymes:isocitrate dehydrogenase, alpha-ketoglutarate:ferredoxin oxidoreductase, pyruvate:ferredoxin oxidoreductase. The presence of ATP-citrate lyase or citrate lyase and alpha-ketoglutarate:ferredoxin oxidoreductase indicates the presence of an active reductive TCA cycle in an organism. Enzymes for each step of the reductive TCA cycle are shown below.
ATP-citrate lyase (ACL, EC 2.3.3.8), also called ATP citrate synthase, catalyzes the ATP-dependent cleavage of citrate to oxaloacetate and acetyl-CoA. ACL is an enzyme of the RTCA cycle that has been studied in green sulfur bacteria Chlorobium limicola and Chlorobium tepidum. The alpha(4)beta(4) heteromeric enzyme from Chlorobium limicola was cloned and characterized in E. coli (Kanao et al., Eur. J. Biochem. 269:3409-3416 (2002). The C. limicola enzyme, encoded by aclAB, is irreversible and activity of the enzyme is regulated by the ratio of ADP/ATP. A recombinant ACL from Chlorobium tepidum was also expressed in E. coli and the holoenzyme was reconstituted in vitro, in a study elucidating the role of the alpha and beta subunits in the catalytic mechanism (Kim and Tabita, J. Bacteriol. 188:6544-6552 (2006). ACL enzymes have also been identified in Balnearium lithotrophicum, Sulfurihydrogenibium subterraneum and other members of the bacterial phylum Aquificae (Hugler et al., Environ. Microbiol. 9:81-92 (2007)). This activity has been reported in some fungi as well. Exemplary organisms include Sordaria macrospora (Nowrousian et al., Curr. Genet. 37:189-93 (2000), Aspergillus nidulans, Yarrowia lipolytica (Hynes and Murray, Eukaryotic Cell, July: 1039-1048, (2010) and Aspergillus niger (Meijer et al. J. Ind. Microbiol. Biotechnol. 36:1275-1280 (2009). Other candidates can be found based on sequence homology. Information related to these enzymes is tabulated below:


Protein	GenBank ID	GI Number	Organism

aclA	BAB21376.1	12407237	Chlorobium limicola
aclB	BAB21375.1	12407235	Chlorobium limicola
aclA	AAM72321.1	21647054	Chlorobium tepidum
aclB	AAM72322.1	21647055	Chlorobium tepidum
aclA	ABI50076.1	114054981	Balnearium
			lithotrophicum
aclB	ABI50075.1	114054980	Balnearium
			lithotrophicum
aclA	ABI50085.1	114055040	Sulfurihydrogenibium
			subterraneum
aclB	ABI50084.1	114055039	Sulfurihydrogenibium
			subterraneum
aclA	AAX76834.1	62199504	Sulfurimonas
			denitrificans
aclB	AAX76835.1	62199506	Sulfurimonas
			denitrificans
acl1	XP_504787.1	50554757	Yarrowia lipolytica
acl2	XP_503231.1	50551515	Yarrowia lipolytica
SPBC1703.07	NP_596202.1	19112994	Schizosaccharomyces
			pombe
SPAC22A12.16	NP_593246.1	19114158	Schizosaccharomyces
			pombe
acl1	CAB76165.1	7160185	Sordaria macrospora
acl2	CAB76164.1	7160184	Sordaria macrospora
aclA	CBF86850.1	259487849	Aspergillus nidulans
aclB	CBF86848	259487848	Aspergillus nidulans

In some organisms the conversion of citrate to oxaloacetate and acetyl-CoA proceeds through a citryl-CoA intermediate and is catalyzed by two separate enzymes, citryl-CoA synthetase (EC 6.2.1.18) and citryl-CoA lyase (EC 4.1.3.34) (Aoshima, M., Appl. Microbiol. Biotechnol. 75:249-255 (2007). Citryl-CoA synthetase catalyzes the activation of citrate to citryl-CoA. The Hydrogenobacter thermophilus enzyme is composed of large and small subunits encoded by ccsA and ccsB, respectively (Aoshima et al., Mol. Micrbiol. 52:751-761 (2004)). The citryl-CoA synthetase of Aquifex aeolicus is composed of alpha and beta subunits encoded by sucC1 and sucD1 (Hugler et al., Environ. Microbiol. 9:81-92 (2007)). Citryl-CoA lyase splits citryl-CoA into oxaloacetate and acetyl-CoA. This enzyme is a homotrimer encoded by ccl in Hydrogenobacter thermophilus (Aoshima et al., Mol. Microbiol. 52:763-770 (2004)) and aq_150 in Aquifex aeolicus (Hugler et al., supra (2007)). The genes for this mechanism of converting citrate to oxaloacetate and citryl-CoA have also been reported recently in Chlorobium tepidum (Eisen et al., PNAS 99(14): 9509-14 (2002).


Protein	GenBank ID	GI Number	Organism

ccsA	BAD17844.1	46849514	Hydrogenobacter thermophilus
ccsB	BAD17846.1	46849517	Hydrogenobacter thermophilus
sucC1	AAC07285	2983723	Aquifex aeolicus
sucD1	AAC07686	2984152	Aquifex aeolicus
ccl	BAD17841.1	46849510	Hydrogenobacter thermophilus
aq_150	AAC06486	2982866	Aquifex aeolicus
CT0380	NP_661284	21673219	Chlorobium tepidum
CT0269	NP_661173.1	21673108	Chlorobium tepidum
CT1834	AAM73055.1	21647851	Chlorobium tepidum

Oxaloacetate is converted into malate by malate dehydrogenase (EC 1.1.1.37), an enzyme which functions in both the forward and reverse direction. S. cerevisiae possesses three copies of malate dehydrogenase, MDH1 (McAlister-Henn and Thompson, J. Bacteriol. 169:5157-5166 (1987), MDH2 (Minard and McAlister-Henn, Mol. Cell. Biol. 11:370-380 (1991); Gibson and McAlister-Henn, J. Biol. Chem. 278:25628-25636 (2003)), and MDH3 (Steffan and McAlister-Henn, J. Biol. Chem. 267:24708-24715 (1992)), which localize to the mitochondrion, cytosol, and peroxisome, respectively. E. coli is known to have an active malate dehydrogenase encoded by mdh.


Protein	GenBank ID	GI Number	Organism

MDH1	NP_012838	6322765	Saccharomyces cerevisiae
MDH2	NP_014515	116006499	Saccharomyces cerevisiae
MDH3	NP_010205	6320125	Saccharomyces cerevisiae
Mdh	NP_417703.1	16131126	Escherichia coli

Fumarate hydratase (EC 4.2.1.2) catalyzes the reversible hydration of fumarate to malate. The three fumarases of E. coli, encoded by fumA, fumB and fumC, are regulated under different conditions of oxygen availability. FumB is oxygen sensitive and is active under anaerobic conditions. FumA is active under microanaerobic conditions, and FumC is active under aerobic growth conditions (Tseng et al., J. Bacteriol. 183:461-467 (2001); Woods et al., Biochim. Biophys. Acta 954:14-26 (1988); Guest et al., J. Gen. Microbiol. 131:2971-2984 (1985)). S. cerevisiae contains one copy of a fumarase-encoding gene, FUM1, whose product localizes to both the cytosol and mitochondrion (Sass et al., J. Biol. Chem. 278:45109-45116 (2003)). Additional fumarase enzymes are found in Campylobacter jejuni (Smith et al., Int. J Biochem. Cell. Biol. 31:961-975 (1999)), Thermus thermophilus (Mizobata et al., Arch. Biochem. Biophys. 355:49-55 (1998)) and Rattus norvegicus (Kobayashi et al., J. Biochem. 89:1923-1931 (1981)). Similar enzymes with high sequence homology include fum1 from Arabidopsis thaliana and fumC from Corynebacterium glutamicum. The MmcBC fumarase from Pelotomaculum thermopropionicum is another class of fumarase with two subunits (Shimoyama et al., FEMS Microbiol. Lett. 270:207-213 (2007)).


Protein	GenBank ID	GI Number	Organism

fumA	NP_416129.1	16129570	Escherichia coli
fumB	NP_418546.1	16131948	Escherichia coli
fumC	NP_416128.1	16129569	Escherichia coli
FUM1	NP_015061	6324993	Saccharomyces cerevisiae
fumC	Q8NRN8.1	39931596	Corynebacterium glutamicum
fumC	O69294.1	9789756	Campylobacter jejuni
fumC	P84127	75427690	Thermus thermophilus
fumH	P14408.1	120605	Rattus norvegicus
MmcB	YP_001211906	147677691	Pelotomaculum
			thermopropionicum
MmcC	YP_001211907	147677692	Pelotomaculum
			thermopropionicum

Fumarate reductase catalyzes the reduction of fumarate to succinate. The fumarate reductase of E. coli, composed of four subunits encoded by frdABCD, is membrane-bound and active under anaerobic conditions. The electron donor for this reaction is menaquinone and the two protons produced in this reaction do not contribute to the proton gradient (Iverson et al., Science 284:1961-1966 (1999)). The yeast genome encodes two soluble fumarate reductase isozymes encoded by FRDS1 (Enomoto et al., DNA Res. 3:263-267 (1996)) and FRDS2 (Muratsubaki et al., Arch. Biochem. Biophys. 352:175-181 (1998)), which localize to the cytosol and promitochondrion, respectively, and are used during anaerobic growth on glucose (Arikawa et al., FEMS Microbiol. Lett. 165:111-116 (1998)).


Protein	GenBank ID	GI Number	Organism

FRDS1	P32614	418423	Saccharomyces cerevisiae
FRDS2	NP_012585	6322511	Saccharomyces cerevisiae
frdA	NP_418578.1	16131979	Escherichia coli
frdB	NP_418577.1	16131978	Escherichia coli
frdC	NP_418576.1	16131977	Escherichia coli
frdD	NP_418475.1	16131877	Escherichia coli

The ATP-dependent acylation of succinate to succinyl-CoA is catalyzed by succinyl-CoA synthetase (EC 6.2.1.5). The product of the LSC1 and LSC2 genes of S. cerevisiae and the sucC and sucD genes of E. coli naturally form a succinyl-CoA synthetase complex that catalyzes the formation of succinyl-CoA from succinate with the concomitant consumption of one ATP, a reaction which is reversible in vivo (Buck et al., Biochemistry 24:6245-6252 (1985)). These proteins are identified below:


Protein	GenBank ID	GI Number	Organism

LSC1	NP_014785	6324716	Saccharomyces cerevisiae
LSC2	NP_011760	6321683	Saccharomyces cerevisiae
sucC	NP_415256.1	16128703	Escherichia coli
sucD	AAC73823.1	1786949	Escherichia coli

Alpha-ketoglutarate:ferredoxin oxidoreductase (EC 1.2.7.3), also known as 2-oxoglutarate synthase or 2-oxoglutarate:ferredoxin oxidoreductase (OFOR), forms alpha-ketoglutarate from CO2 and succinyl-CoA with concurrent consumption of two reduced ferredoxin equivalents. OFOR and pyruvate:ferredoxin oxidoreductase (PFOR) are members of a diverse family of 2-oxoacid:ferredoxin (flavodoxin) oxidoreductases which utilize thiamine pyrophosphate, CoA and iron-sulfur clusters as cofactors and ferredoxin, flavodoxin and FAD as electron carriers (Adams et al., Archaea. Adv. Protein Chem. 48:101-180 (1996)). Enzymes in this class are reversible and function in the carboxylation direction in organisms that fix carbon by the RTCA cycle such as Hydrogenobacter thermophilus, Desulfobacter hydrogenophilus and Chlorobium species (Shiba et al. 1985; Evans et al., Proc. Natl. Acad. Sci. U.S.A. 55:92934 (1966); Buchanan, 1971). The two-subunit enzyme from H. thermophilus, encoded by korAB, has been cloned and expressed in E. coli (Yun et al., Biochem. Biophys. Res. Commun. 282:589-594 (2001)). A five subunit OFOR from the same organism with strict substrate specificity for succinyl-CoA, encoded by forDABGE, was recently identified and expressed in E. coli (Yun et al., Biochem. Biophys. Res. Commun. 292:280-286 (2002)). The kinetics of CO2 fixation of both H. thermophilus OFOR enzymes have been characterized (Yamamoto et al., Extremophiles 14:79-85 (2010)). A CO2-fixing OFOR from Chlorobium thiosulfatophilum has been purified and characterized but the genes encoding this enzyme have not been identified to date. Enzyme candidates in Chlorobium species can be inferred by sequence similarity to the H. thermophilus genes. For example, the Chlorobium limicola genome encodes two similar proteins. Acetogenic bacteria such as Moorella thermoacetica are predicted to encode two OFOR enzymes. The enzyme encoded by Moth_0034 is predicted to function in the CO2-assimilating direction. The genes associated with this enzyme, Moth_0034 have not been experimentally validated to date but can be inferred by sequence similarity to known OFOR enzymes.
OFOR enzymes that function in the decarboxylation direction under physiological conditions can also catalyze the reverse reaction. The OFOR from the thermoacidophilic archaeon Sulfolobus sp. strain 7, encoded by ST2300, has been extensively studied (Zhang et al., supra, 1996). A plasmid-based expression system has been developed for efficiently expressing this protein in E. coli (Fukuda et al., Eur. J. Biochem. 268:5639-5646 (2001)) and residues involved in substrate specificity were determined (Fukuda and Wakagi, Biochim. Biophys. Acta 1597:74-80 (2002)). The OFOR encoded by Ape1472/Ape1473 from Aeropyrum pernix str. K1 was recently cloned into E. coli, characterized, and found to react with 2-oxoglutarate and a broad range of 2-oxoacids (Nishizawa et al., FEBS Lett. 579:2319-2322 (2005)). Another exemplary OFOR is encoded by oorDABC in Helicobacter pylori (Hughes et al., J. Bacteriol. 180:1119-1128 (1998)). An enzyme specific to alpha-ketoglutarate has been reported in Thauera aromatica (Dorner and Boll, J. Bacteriol. 184 (14), 3975-83 (2002)). A similar enzyme can be found in Rhodospirillum rubrum by sequence homology. A two subunit enzyme has also been identified in Chlorobium tepidum (Eisen et al., Proc. Natl. Acad. Sci. USA 99(14): 9509-9514 (2002)).


Protein	GenBank ID	GI Number	Organism

korA	BAB21494	12583691	Hydrogenobacter
			thermophilus
korB	BAB21495	12583692	Hydrogenobacter
			thermophilus
forD	BAB62132.1	14970994	Hydrogenobacter
			thermophilus
forA	BAB62133.1	14970995	Hydrogenobacter
			thermophilus
forB	BAB62134.1	14970996	Hydrogenobacter
			thermophilus
forG	BAB62135.1	14970997	Hydrogenobacter
			thermophilus
forE	BAB62136.1	14970998	Hydrogenobacter
			thermophilus
Clim 0204	ACD89303.1	189339900	Chlorobium limicola
Clim_0205	ACD89302.1	189339899	Chlorobium limicola
Clim_1123	ACD90192.1	189340789	Chlorobium limicola
Clim_1124	ACD90193.1	189340790	Chlorobium limicola
Moth_1984	YP_430825.1	83590816	Moorella thermoacetica
Moth 1985	YP_430826.1	83590817	Moorella thermoacetica
Moth_0034	YP_428917.1	83588908	Moorella thermoacetica
ST2300	NP_378302.1	15922633	Sulfolobus sp. strain 7
Ape1472	BAA80470.1	5105156	Aeropyrum pernix
Ape1473	BAA80471.2	116062794	Aeropyrum pernix
oorD	NP_207383.1	15645213	Helicobacter pylori
oorA	NP_207384.1	15645214	Helicobacter pylori
oorB	NP_207385.1	15645215	Helicobacter pylori
oorC	NP_207386.1	15645216	Helicobacter pylori
CT0163	NP_661069.1	21673004	Chlorobium tepidum
CT0162	NP_661068.1	21673003	Chlorobium tepidum
korA	CAA12243.2	19571179	Thauera aromatica
korB	CAD27440.1	19571178	Thauera aromatica
Rru_A2721	YP_427805.1	83594053	Rhodospirillum rubrum
Rru_A2722	YP_427806.1	83594054	Rhodospirillum rubrum

Isocitrate dehydrogenase catalyzes the reversible decarboxylation of isocitrate to 2-oxoglutarate coupled to the reduction of NAD(P)⁺. IDH enzymes in Saccharomyces cerevisiae and Escherichia coli are encoded by IDP1 and icd, respectively (Haselbeck and McAlister-Henn, J. Biol. Chem. 266:2339-2345 (1991); Nimmo, Biochem. J. 234:317-2332 (1986)). The reverse reaction in the reductive TCA cycle, the reductive carboxylation of 2-oxoglutarate to isocitrate, is favored by the NADPH-dependent CO₂-fixing IDH from Chlorobium limicola and was functionally expressed in E. coli (Kanao et al., Eur. J. Biochem. 269:1926-1931 (2002)). A similar enzyme with 95% sequence identity is found in the C. tepidum genome in addition to some other candidates listed below.


Protein	GenBank ID	GI Number	Organism

Icd	ACI84720.1	209772816	Escherichia coli
IDP1	AAA34703.1	171749	Saccharomyces cerevisiae
Idh	BAC00856.1	21396513	Chlorobium limicola
Icd	AAM71597.1	21646271	Chlorobium tepidum
icd	NP_952516.1	39996565	Geobacter sulfurreducens
icd	YP_393560.	78777245	Sulfurimonas denitrificans

In H. thermophilus the reductive carboxylation of 2-oxoglutarate to isocitrate is catalyzed by two enzymes: 2-oxoglutarate carboxylase and oxalosuccinate reductase. 2-Oxoglutarate carboxylase (EC 6.4.1.7) catalyzes the ATP-dependent carboxylation of alpha-ketoglutarate to oxalosuccinate (Aoshima and Igarashi, Mol. Microbiol. 62:748-759 (2006)). This enzyme is a large complex composed of two subunits. Biotinylation of the large (A) subunit is required for enzyme function (Aoshima et al., Mol. Microbiol. 51:791-798 (2004)). Oxalosuccinate reductase (EC 1.1.1.-) catalyzes the NAD-dependent conversion of oxalosuccinate to D-threo-isocitrate. The enzyme is a homodimer encoded by icd in H. thermophilus. The kinetic parameters of this enzyme indicate that the enzyme only operates in the reductive carboxylation direction in vivo, in contrast to isocitrate dehydrogenase enzymes in other organisms (Aoshima and Igarashi, J. Bacteriol. 190:2050-2055 (2008)). Based on sequence homology, gene candidates have also been found in Thiobacillus denitrificans and Thermocrinis albus.


Protein	GenBank ID	GI Number	Organism

cfiA	BAF34932.1	116234991	Hydrogenobacter thermophilus
cifB	BAF34931.1	116234990	Hydrogenobacter thermophilus
Icd	BAD02487.1	38602676	Hydrogenobacter thermophilus
Tbd_1556	YP_315314	74317574	Thiobacillus denitrificans
Tbd_1555	YP_315313	74317573	Thiobacillus denitrificans
Tbd_0854	YP_314612	74316872	Thiobacillus denitrificans
Thal_0268	YP_003473030	289548042	Thermocrinis albus
Thal_0267	YP_003473029	289548041	Thermocrinis albus
Thal_0646	YP_003473406	289548418	Thermocrinis albus

Aconitase (EC 4.2.1.3) is an iron-sulfur-containing protein catalyzing the reversible isomerization of citrate and iso-citrate via the intermediate cis-aconitate. Two aconitase enzymes are encoded in the E. coli genome by acnA and acnB. AcnB is the main catabolic enzyme, while AcnA is more stable and appears to be active under conditions of oxidative or acid stress (Cunningham et al., Microbiology 143 (Pt 12):3795-3805 (1997)). Two isozymes of aconitase in Salmonella typhimurium are encoded by acnA and acnB (Horswill and Escalante-Semerena, Biochemistry 40:4703-4713 (2001)). The S. cerevisiae aconitase, encoded by ACO1, is localized to the mitochondria where it participates in the TCA cycle (Gangloff et al., Mol. Cell. Biol. 10:3551-3561 (1990)) and the cytosol where it participates in the glyoxylate shunt (Regev-Rudzki et al., Mol. Biol. Cell. 16:4163-4171 (2005)).


Protein	GenBank ID	GI Number	Organism

acnA	AAC7438.1	1787531	Escherichia coli
acnB	AAC73229.1	2367097	Escherichia coli
acnA	NP_460671.1	16765056	Salmonella typhimurium
HP0779	NP_207572.1	15645398	Helicobacter pylori 26695
H16_B0568	CAJ95365.1	113529018	Ralstonia eutropha
DesfrDRAFT_3783	ZP_07335307.1	303249064	Desulfovibrio fructosovorans JJ
Suden_1040	ABB44318.1	78497778	Sulfurimonas denitrificans
(acnB)
Hydth 0755	ADO45152.1	308751669	Hydrogenobacter thermophilus
CT0543 (acn)	AAM71785.1	21646475	Chlorobium tepidum
Clim 2436	YP_001944436.1	189347907	Chlorobium limicola
Clim_0515	ACD89607.1	189340204	Chlorobium limicola
acnB	NP_459163.1	16763548	Salmonella typhimurium
ACO1	AAA34389.1	170982	Saccharomyces cerevisiae

Pyruvate:ferredoxin oxidoreductase (PFOR) catalyzes the reversible oxidation of pyruvate to form acetyl-CoA. The PFOR from Desulfovibrio africanus has been cloned and expressed in E. coli resulting in an active recombinant enzyme that was stable for several days in the presence of oxygen (Pieulle et al., J. Bacteriol. 179:5684-5692 (1997)). Oxygen stability is relatively uncommon in PFORs and is believed to be conferred by a 60 residue extension in the polypeptide chain of the D. africanus enzyme. Two cysteine residues in this enzyme form a disulfide bond that prtotects it against inactivation in the form of oxygen. This disulfide bond and the stability in the presence of oxygen has been found in other Desulfovibrio species also (Vita et al., Biochemistry, 47: 957-64 (2008)). The M. thermoacetica PFOR is also well characterized (Menon and Ragsdale, Biochemistry 36:8484-8494 (1997)) and was shown to have high activity in the direction of pyruvate synthesis during autotrophic growth (Furdui and Ragsdale, J. Biol. Chem. 275:28494-28499 (2000)). Further, E. coli possesses an uncharacterized open reading frame, ydbK, encoding a protein that is 51% identical to the M. thermoacetica PFOR. Evidence for pyruvate oxidoreductase activity in E. coli has been described (Blaschkowski et al., Eur. J. Biochem. 123:563-569 (1982)). PFORs have also been described in other organisms, including Rhodobacter capsulatas (Yakunin and Hallenbeck, Biochimica et Biophysica Acta 1409 (1998) 39-49 (1998)) and Choloboum tepidum (Eisen et al., Proc. Natl. Acad. Sci. USA 99(14): 9509-14 (2002)). The five subunit PFOR from H. thermophilus, encoded by porEDABG, was cloned into E. coli and shown to function in both the decarboxylating and CO₂-assimilating directions (Ikeda et al., Biochem. Biophys. Res. Commun. 340:76-82 (2006) 2006; Yamamoto et al., Extremophiles 14:79-85 (2010)). Homologs also exist in C. carboxidivorans P7. Several additional PFOR enzymes are described in the following review (Ragsdale, S. W., Chem. Rev. 103:2333-2346 (2003)). Finally, flavodoxin reductases (e.g., fqrB from Helicobacter pylori or Campylobacter jejuni) (St Maurice et al., J. Bacteriol. 189:4764-4773 (2007)) or Rnf-type proteins (Seedorf et al., Proc. Natl. Acad. Sci. U.S.A. 105:2128-2133 (2008); and Herrmann, J. Bacteriol 190:784-791 (2008)) provide a means to generate NADH or NADPH from the reduced ferredoxin generated by PFOR. These proteins are identified below.


Protein	GenBank ID	GI Number	Organism

DesfrDRAFT_0121	ZP_07331646.1	303245362	Desulfovibrio fructosovorans
			JJ
Por	CAA70873.1	1770208	Desulfovibrio africanus
por	YP_012236.1	46581428	Desulfovibrio vulgaris str.
			Hildenborough
Dde_3237	ABB40031.1	78220682	DesulfoVibrio desulfuricans
			G20
Ddes_0298	YP_002478891.1	220903579	Desulfovibrio desulfuricans
			subsp. desulfuricans str.
			ATCC 27774
Por	YP_428946.1	83588937	Moorella thermoacetica
YdbK	NP_415896.1	16129339	Escherichia coli
nifJ (CT1628)	NP_662511.1	21674446	Chlorobium tepidum
CJE1649	YP_179630.1	57238499	Campylobacter jejuni
nifJ	ADE85473.1	294476085	Rhodobacter capsulatus
porE	BAA95603.1	7768912	Hydrogenobacter thermophilus
porD	BAA95604.1	7768913	Hydrogenobacter thermophilus
porA	BAA95605.1	7768914	Hydrogenobacter thermophilus
porB	BAA95606.1	776891	Hydrogenobacter thermophilus
porG	BAA95607.1	7768916	Hydrogenobacter thermophilus
FqrB	YP_001482096.1	157414840	Campylobacter jejuni
HP1164	NP_207955.1	15645778	Helicobacter pylori
RnfC	EDK33306.1	146346770	Clostridium kluyveri
RnfD	EDK33307.1	146346771	Clostridium kluyveri
RnfG	EDK33308.1	146346772	Clostridium kluyveri
RnfE	EDK33309.1	146346773	Clostridium kluyveri
RnfA	EDK33310.1	146346774	Clostridium kluyveri
RnfB	EDK33311.1	146346775	Clostridium kluyveri

The conversion of pyruvate into acetyl-CoA can be catalyzed by several other enzymes or their combinations thereof. For example, pyruvate dehydrogenase can transform pyruvate into acetyl-CoA with the concomitant reduction of a molecule of NAD into NADH. It is a multi-enzyme complex that catalyzes a series of partial reactions which results in acylating oxidative decarboxylation of pyruvate. The enzyme comprises of three subunits: the pyruvate decarboxylase (E1), dihydrolipoamide acyltransferase (E2) and dihydrolipoamide dehydrogenase (E3). This enzyme is naturally present in several organisms, including E. coli and S. cerevisiae. In the E. coli enzyme, specific residues in the E1 component are responsible for substrate specificity (Bisswanger, J. Biol. Chem. 256:815-82 (1981); Bremer, Eur. J. Biochem. 8:535-540 (1969); Gong et al., J. Biol. Chem. 275:13645-13653 (2000)). Enzyme engineering efforts have improved the E. coli PDH enzyme activity under anaerobic conditions (Kim et al., J. Bacteriol. 190:3851-3858 (2008); Kim et al., Appl. Environ. Microbiol. 73:1766-1771 (2007); Zhou et al., Biotechnol. Lett. 30:335-342 (2008)). In contrast to the E. coli PDH, the B. subtilis complex is active and required for growth under anaerobic conditions (Nakano et al., J. Bacteriol. 179:6749-6755 (1997)). The Klebsiella pneumoniae PDH, characterized during growth on glycerol, is also active under anaerobic conditions (5). Crystal structures of the enzyme complex from bovine kidney (18) and the E2 catalytic domain from Azotobacter vinelandii are available (4). Yet another enzyme that can catalyze this conversion is pyruvate formate lyase. This enzyme catalyzes the conversion of pyruvate and CoA into acetyl-CoA and formate. Pyruvate formate lyase is a common enzyme in prokaryotic organisms that is used to help modulate anaerobic redox balance. Exemplary enzymes can be found in Escherichia coli encoded by pflB (Knappe and Sawers, FEMS. Microbiol Rev. 6:383-398 (1990)), Lactococcus lactis (Melchiorsen et al., Appl Microbiol Biotechnol 58:338-344 (2002)), and Streptococcus mutans (Takahashi-Abbe et al., Oral. Microbiol Immunol. 18:293-297 (2003)). E. coli possesses an additional pyruvate formate lyase, encoded by tdcE, that catalyzes the conversion of pyruvate or 2-oxobutanoate to acetyl-CoA or propionyl-CoA, respectively (Hesslinger et al., Mol. Microbiol 27:477-492 (1998)). Both pflB and tdcE from E. coli require the presence of pyruvate formate lyase activating enzyme, encoded by pflA. Further, a short protein encoded by yfiD in E. coli can associate with and restore activity to oxygen-cleaved pyruvate formate lyase (Vey et al., Proc. Natl. Acad. Sci. U.S.A. 105:16137-16141 (2008). Note that pflA and pflB from E. coli were expressed in S. cerevisiae as a means to increase cytosolic acetyl-CoA for butanol production as described in WO/2008/080124. Additional pyruvate formate lyase and activating enzyme candidates, encoded by pfl and act, respectively, are found in Clostridium pasteurianum (Weidner et al., J Bacteriol. 178:2440-2444 (1996)).
Further, different enzymes can be used in combination to convert pyruvate into acetyl-CoA. For example, in S. cerevisiae, acetyl-CoA is obtained in the cytosol by first decarboxylating pyruvate to form acetaldehyde; the latter is oxidized to acetate by acetaldehyde dehydrogenase and subsequently activated to form acetyl-CoA by acetyl-CoA synthetase. Acetyl-CoA synthetase is a native enzyme in several other organisms including E. coli (Kumari et al., J. Bacteriol. 177:2878-2886 (1995)), Salmonella enterica (Starai et al., Microbiology 151:3793-3801 (2005); Starai et al., J. Biol. Chem. 280:26200-26205 (2005)), and Moorella thermoacetica (described already). Alternatively, acetate can be activated to form acetyl-CoA by acetate kinase and phosphotransacetylase. Acetate kinase first converts acetate into acetyl-phosphate with the accompanying use of an ATP molecule. Acetyl-phosphate and CoA are next converted into acetyl-CoA with the release of one phosphate by phosphotransacetylase. Both acetate kinase and phosphotransacetlyase are well-studied enzymes in several Clostridia and Methanosarcina thermophila.
Yet another way of converting pyruvate to acetyl-CoA is via pyruvate oxidase. Pyruvate oxidase converts pyruvate into acetate, using ubiquione as the electron acceptor. In E. coli, this activity is encoded by poxB. PoxB has similarity to pyruvate decarboxylase of S. cerevisiae and Zymomonas mobilis. The enzyme has a thiamin pyrophosphate cofactor (Koland and Gennis, Biochemistry 21:4438-4442 (1982)); O'Brien et al., Biochemistry 16:3105-3109 (1977); O'Brien and Gennis, J. Biol. Chem. 255:3302-3307 (1980)) and a flavin adenine dinucleotide (FAD) cofactor. Acetate can then be converted into acetyl-CoA by either acetyl-CoA synthetase or by acetate kinase and phosphotransacetylase, as described earlier. Some of these enzymes can also catalyze the reverse reaction from acetyl-CoA to pyruvate.
For enzymes that use reducing equivalents in the form of NADH or NADPH, these reduced carriers can be generated by transferring electrons from reduced ferredoxin. Two enzymes catalyze the reversible transfer of electrons from reduced ferredoxins to NAD(P)⁺, ferredoxin:NAD⁺ oxidoreductase (EC 1.18.1.3) and ferredoxin:NADP⁺ oxidoreductase (FNR, EC 1.18.1.2). Ferredoxin:NADP⁺ oxidoreductase (FNR, EC 1.18.1.2) has a noncovalently bound FAD cofactor that facilitates the reversible transfer of electrons from NADPH to low-potential acceptors such as ferredoxins or flavodoxins (Blaschkowski et al., Eur. J. Biochem. 123:563-569 (1982); Fujii et al., 1977). The Helicobacter pylori FNR, encoded by HP1164 (fqrB), is coupled to the activity of pyruvate:ferredoxin oxidoreductase (PFOR) resulting in the pyruvate-dependent production of NADPH (St. Maurice et al., J Bacteriol. 189(13):4764-4773 (2007)). An analogous enzyme is found in Campylobacter jejuni (St. Maurice et al., supra, 2007). A ferredoxin:NADP⁺ oxidoreductase enzyme is encoded in the E. coli genome by fpr (Bianchi et al., J Bacteriol. 175:1590-1595 (1993)). Ferredoxin:NAD⁺ oxidoreductase utilizes reduced ferredoxin to generate NADH from NAD⁺. In several organisms, including E. coli, this enzyme is a component of multifunctional dioxygenase enzyme complexes. The ferredoxin:NAD⁺ oxidoreductase of E. coli, encoded by hcaD, is a component of the 3-phenylproppionate dioxygenase system involved in involved in aromatic acid utilization (Diaz et al., J. Bacteriol. 180:2915-2923 (1998)). NADH:ferredoxin reductase activity was detected in cell extracts of Hydrogenobacter thermophilus strain TK-6, although a gene with this activity has not yet been indicated (Yoon et al. 2006). NADP oxidoreductase of C. kluyveri, encoded by nfnAB, catalyzes the concomitant reduction of ferredoxin and NAD+ with two equivalents of NADPH (Wang et al, J. Bacteriol. 192: 5115-5123 (2010)). Finally, the energy-conserving membrane-associated Rnf-type proteins (Seedorf et al., Proc. Natl. Acad. Sci. U.S.A. 105:2128-2133 (2008); Herrmann et al., J. Bacteriol. 190:784-791 (2008)) provide a means to generate NADH or NADPH from reduced ferredoxin. Additional ferredoxin:NAD(P)+ oxidoreductases have been annotated in Clostridium carboxydivorans P7 and Clostridium ljungdahli.


Protein	GenBank ID	GI Number	Organism

HP1164	NP_207955.1	15645778	Helicobacter pylori
RPA3954	CAE29395.1	39650872	Rhodopseudomonas palustris
fpr	BAH29712.1	225320633	Hydrogenobacter thermophilus
yumC	NP_391091.2	255767736	Bacillus subtilis
CJE0663	AAW35824.1	57167045	Campylobacter jejuni
fpr	P28861.4	399486	Escherichia coli
hcaD	AAC75595.1	1788892	Escherichia coli
LOC100282643	NP_001149023.1	226497434	Zea mays
NfnA	YP_001393861.1	153953096	Clostridium kluyveri
NfnB	YP_001393862.1	153953097	Clostridium kluyveri
RnfC	EDK33306.1	146346770	Clostridium kluyveri
RnfD	EDK33307.1	146346771	Clostridium kluyveri
RnfG	EDK33308.1	146346772	Clostridium kluyveri
RnfE	EDK33309.1	146346773	Clostridium kluyveri
RnfA	EDK33310.1	146346774	Clostridium kluyveri
RnfB	EDK33311.1	146346775	Clostridium kluyveri
CcarbDRAFT_2639	ZP_05392639.1	255525707	Clostridium carboxidivorans
			P7
CcarbDRAFT_2638	ZP_05392638.1	255525706	Clostridium carboxidivorans
			P7
CcarbDRAFT_2636	ZP_05392636.1	255525704	Clostridium carboxidivorans
			P7
CcarbDRAFT_5060	ZP_05395060.1	255528241	Clostridium carboxidivorans
			P7
CcarbDRAFT_2450	ZP_05392450.1	255525514	Clostridium carboxidivorans
			P7
CcarbDRAFT_1084	ZP_05391084.1	255524124	Clostridium carboxidivorans
			P7
CLJU_c11410	ADK14209.1	300434442	Clostridium ljungdahli
(RnfB)
CLJU_c11400	ADK14208.1	300434441	Clostridium ljungdahli
(RnfA)
CLJU_c11390	ADK14207.1	300434440	Clostridium ljungdahli
(RnfE)
CLJU_c11380	ADK14206.1	300434439	Clostridium ljungdahli
(RnfG)
CLJU_c11370	ADK14205.1	300434438	Clostridium ljungdahli
(RnfD)
CLJU_c11360	ADK14204.1	300434437	Clostridium ljungdahli
(RnfC)

Ferredoxins are small acidic proteins containing one or more iron-sulfur clusters that function as intracellular electron carriers with a low reduction potential. Reduced ferredoxins donate electrons to Fe-dependent enzymes such as ferredoxin-NADP⁺ oxidoreductase, pyruvate:ferredoxin oxidoreductase (PFOR) and 2-oxoglutarate:ferredoxin oxidoreductase (OFOR). The H. thermophilus gene fdx1 encodes a [4Fe-4S]-type ferredoxin that is required for the reversible carboxylation of 2-oxoglutarate and pyruvate by OFOR and PFOR, respectively (Yamamoto et al., Extremophiles 14:79-85 (2010)). The ferredoxin associated with the Sulfolobus solfataricus 2-oxoacid:ferredoxin reductase is a monomeric dicluster [3Fe-4S][4Fe-4S] type ferredoxin (Park et al., J Biochem Mol Biol. 39:46-54 (2006)). While the gene associated with this protein has not been fully sequenced, the N-terminal domain shares 93% homology with the zfx ferredoxin from S. acidocaldarius. The E. coli genome encodes a soluble ferredoxin of unknown physiological function, fdx. Some evidence indicates that this protein can function in iron-sulfur cluster assembly (Takahashi and Nakamura, J Biochem. 126:917-926 (1999)). Additional ferredoxin proteins have been characterized in Helicobacter pylori (Mukhopadhyay et al., J Bacteriol. 185:2927-2935 (2003)) and Campylobacter jejuni (van Vliet et al., FEMS Microbiol Lett. 196:189-193 (2001)). A 2Fe-2S ferredoxin from Clostridium pasteurianum has been cloned and expressed in E. coli (Fujinaga and Meyer, Biochemical and Biophysical Research Communications, 192(3): 1115-1122 (1993)). Acetogenic bacteria such as Moorella thermoacetica, Clostridium carboxidivorans P7, Clostridium ljungdahli and Rhodospirillum rubrum are predicted to encode several ferredoxins, listed in the table below.


Protein	GenBank ID	GI Number	Organism

fdx1	BAE02673.1	68163284	Hydrogenobacter thermophilus
M11214.1	AAA83524.1	144806	Clostridium pasteurianum
Zfx	AAY79867.1	68566938	Sulfolobiis acidocalarius
Fdx	AAC75578.1	1788874	Escherichia coli
hp_0277	AAD07340.1	2313367	Helicobacter pylori
fdxA	CAL34484.1	112359698	Campylobacter jejuni
Moth_0061	ABC18400.1	83571848	Moorella thermoacetica
Moth_1200	ABC19514.1	83572962	Moorella thermoacetica
Moth 1888	ABC20188.1	83573636	Moorella thermoacetica
Moth_2112	ABC20404.1	83573852	Moorella thermoacetica
Moth_1037	ABC19351.1	83572799	Moorella thermoacetica
CcarbDRAFT_4383	ZP_05394383.1	255527515	Clostridium carboxidivorans
			P7
CcarbDRAFT_2958	ZP_05392958.1	255526034	Clostridium carboxidivorans
			P7
CcarbDRAFT_2281	ZP_05392281.1	255525342	Clostridium carboxidivorans
			P7
CcarbDRAFT_5296	ZP_05395295.1	255528511	Clostridium carboxidivorans
			P7
CcarbDRAFT_1615	ZP_05391615.1	255524662	Clostridium carboxidivorans
			P7
CcarbDRAFT_1304	ZP_05391304.1	255524347	Clostridium carboxidivorans
			P7
cooF	AAG29808.1	11095245	Carboxydothermus hydrogenoformans
fdxN	CAA35699.1	46143	Rhodobacter capsulatus
Rru_A2264	ABC23064.1	83576513	Rhodospirillum rubrum
Rru_A1916	ABC22716.1	83576165	Rhodospirillum rubrum
Rru_A2026	ABC22826.1	83576275	Rhodospirillum rubrum
cooF	AAC45122.1	1498747	Rhodospirillum rubrum
fdxN	AAA26460.1	152605	Rhodospirillum rubrum
Alvin_2884	ADC63789.1	288897953	Allochromatium vinosum
			DSM 180
fdx	YP_002801146.1	226946073	Azotobacter vinelandii DJ
CKL_3790	YP_001397146.1	153956381	Clostridium kluyveri DSM 555
fer1	NP_949965.1	39937689	Rhodopseudomonas palustris
			CGA009
fdx	CAA12251.1	3724172	Thauera aromatica
CHY_2405	YP_361202.1	78044690	Carboxydothermus hydrogenoformans
fer	YP_359966.1	78045103	Carboxydothermus hydrogenoformans
fer	AAC83945.1	1146198	Bacillus subtilis
fdx1	NP_249053.1	15595559	Pseudomonas aeruginosa PA01
yfhL	AP_003148.1	89109368	Escherichia coli K-12
CLJU_c00930	ADK13195.1	300433428	Clostridium ljungdahli
CLJU_c00010	ADK13115.1	300433348	Clostridium ljungdahli
CLJU_c01820	ADK13272.1	300433505	Clostridium ljungdahli
CLJU_c17980	ADK14861.1	300435094	Clostridium ljungdahli
CLJU_c17970	ADK14860.1	300435093	Clostridium ljungdahli
CLJU_c22510	ADK15311.1	300435544	Clostridium ljungdahli
CLJU_c26680	ADK15726.1	300435959	Clostridium ljungdahli
CLJU_c29400	ADK15988.1	300436221	Clostridium ljungdahli

Succinyl-CoA transferase catalyzes the conversion of succinyl-CoA to succinate while transferring the CoA moiety to a CoA acceptor molecule. Many transferases have broad specificity and can utilize CoA acceptors as diverse as acetate, succinate, propionate, butyrate, 2-methylacetoacetate, 3-ketohexanoate, 3-ketopentanoate, valerate, crotonate, 3-mercaptopropionate, propionate, vinylacetate, and butyrate, among others.
The conversion of succinate to succinyl-CoA can be carried by a transferase which does not require the direct consumption of an ATP or GTP. This type of reaction is common in a number of organisms. The conversion of succinate to succinyl-CoA can also be catalyzed by succinyl-CoA:Acetyl-CoA transferase. The gene product of cat1 of Clostridium kluyveri has been shown to exhibit succinyl-CoA:acetyl-CoA transferase activity (Sohling and Gottschalk, J. Bacteriol. 178:871-880 (1996)). In addition, the activity is present in Trichomonas vaginalis (van Grinsven et al., J Biol Chem. 283:1411-1418 (2008)) and Trypanosoma brucei (Riviere et al., J. Biol. Chem. 279(44):45337-45346 (2004)). The succinyl-CoA:acetate CoA-transferase from Acetobacter aceti, encoded by aarC, replaces succinyl-CoA synthetase in a variant TCA cycle (Mullins et al., J. Bacteriol. 190(14):4933-4940 (2008)). Similar succinyl-CoA transferase activities are also present in Trichomonas vaginalis (van Grinsven et al., supra, 2008), Trypanosoma brucei (Riviere et al., supra, 2004) and Clostridium kluyveri (Sohling and Gottschalk, supra, 1996). The beta-ketoadipate:succinyl-CoA transferase encoded by pcaI and pcaJ in Pseudomonas putida is yet another candidate (Kaschabek et al., J. Bacteriol. 184(1):207-215 (2002)). The aforementioned proteins are identified below.


Protein	GenBank ID	GI Number	Organism

cat1	P38946.1	729048	Clostridium kluyveri
TVAG_395550	XP_001330176	123975034	Trichomonas vaginalis G3
Tb11.02.0290	XP_828352	71754875	Trypanosoma brucei
pcaI	AAN69545.1	24985644	Pseudomonas putida
pcaJ	NP_746082.1	26990657	Pseudomonas putida
aarC	ACD85596.1	189233555	Acetobacter aceti

An additional exemplary transferase that converts succinate to succinyl-CoA while converting a 3-ketoacyl-CoA to a 3-ketoacid is succinyl-CoA:3:ketoacid-CoA transferase (EC 2.8.3.5). Exemplary succinyl-CoA:3:ketoacid-CoA transferases are present in Helicobacter pylori (Corthesy-Theulaz et al., J. Biol. Chem. 272(41):25659-25667 (1997)), Bacillus subtilis, and Homo sapiens (Fukao et al., Genomics 68(2): 144-151 (2000); Tanaka et al., Mol. Hum. Reprod. 8(1):16-23 (2002)). The aforementioned proteins are identified below.


Protein	GenBank ID	GI Number	Organism

HPAG1_0676	YP_627417	108563101	Helicobacter pylori
HPAG1_0677	YP_627418	108563102	Helicobacter pylori
ScoA	NP_391778	16080950	Bacillus subtilis
ScoB	NP_391777	16080949	Bacillus subtilis
OXCT1	NP_000427	4557817	Homo sapiens
OXCT2	NP_071403	11545841	Homo sapiens

Converting succinate to succinyl-CoA by succinyl-CoA:3:ketoacid-CoA transferase requires the simultaneous conversion of a 3-ketoacyl-CoA such as acetoacetyl-CoA to a 3-ketoacid such as acetoacetate. Conversion of a 3-ketoacid back to a 3-ketoacyl-CoA can be catalyzed by an acetoacetyl-CoA:acetate:CoA transferase. Acetoacetyl-CoA:acetate:CoA transferase converts acetoacetyl-CoA and acetate to acetoacetate and acetyl-CoA, or vice versa. Exemplary enzymes include the gene products of atoAD from E. coli (Hanai et al., Appl Environ Microbiol 73:7814-7818 (2007), ctfAB from C. acetobutylicum (Jojima et al., Appl Microbiol Biotechnol 77:1219-1224 (2008), and ctfAB from Clostridium saccharoperbutylacetonicum (Kosaka et al., Biosci. Biotechnol Biochem. 71:58-68 (2007)) are shown below.


Protein	GenBank ID	GI Number	Organism

AtoA	NP_416726.1	2492994	Escherichia coli
AtoD	NP_416725.1	2492990	Escherichia coli
CtfA	NP_149326.1	15004866	Clostridium acetobutylicum
CtfB	NP_149327.1	15004867	Clostridium acetobutylicum
CtfA	AAP42564.1	31075384	Clostridium saccharoperbutylacetonicum
CtfB	AAP42565.1	31075385	Clostridium saccharoperbutylacetonicum

Yet another possible CoA acceptor is benzylsuccinate. Succinyl-CoA:(R)-Benzylsuccinate CoA-Transferase functions as part of an anaerobic degradation pathway for toluene in organisms such as Thauera aromatica (Leutwein and Heider, J. Bact. 183(14) 4288-4295 (2001)). Homologs can be found in Azoarcus sp. T, Aromatoleum aromaticum EbN1, and Geobacter metallireducens GS-15. The aforementioned proteins are identified below.


Protein	GenBank ID	GI Number	Organism

bbsE	AAF89840	9622535	Thauera aromatica
Bbsf	AAF89841	9622536	Thauera aromatica
bbsE	AAU45405.1	52421824	Azoarcus sp. T
bbsF	AAU45406.1	52421825	Azoarcus sp. T
bbsE	YP_158075.1	56476486	Aromatoleum aromaticum EbN1
bbsF	YP_158074.1	56476485	Aromatoleum aromaticum EbN1
Gmet 1521	YP_384480.1	78222733	Geobacter metallireducens GS-15
Gmet_1522	YP_384481.1	78222734	Geobacter metallireducens GS-15

Additionally, ygfH encodes a propionyl CoA:succinate CoA transferase in E. coli (Haller et al., Biochemistry, 39(16) 4622-4629). Close homologs can be found in, for example, Citrobacter youngae ATCC 29220, Salmonella enterica subsp. arizonae serovar, and Yersinia intermedia ATCC 29909. The aforementioned proteins are identified below.


Protein	GenBank ID	GI Number	Organism

ygfH	NP_417395.1	16130821	Escherichia coli str. K-12
			substr. MG1655
CIT292 04485	ZP_03838384.1	227334728	Citrobacter youngae ATCC 29220
SARI_04582	YP_001573497.1	161506385	Salmonella enterica subsp.
			arizonae serovar
yinte0001_14430	ZP_04635364.1	238791727	Yersinia intermedia ATCC 29909

Citrate lyase (EC 4.1.3.6) catalyzes a series of reactions resulting in the cleavage of citrate to acetate and oxaloacetate. The enzyme is active under anaerobic conditions and is composed of three subunits: an acyl-carrier protein (ACP, gamma), an ACP transferase (alpha), and a acyl lyase (beta). Enzyme activation uses covalent binding and acetylation of an unusual prosthetic group, 2′-(5″-phosphoribosyl)-3-′-dephospho-CoA, which is similar in structure to acetyl-CoA. Acylation is catalyzed by CitC, a citrate lyase synthetase. Two additional proteins, CitG and CitX, are used to convert the apo enzyme into the active holo enzyme (Schneider et al., Biochemistry 39:9438-9450 (2000)). Wild type E. coli does not have citrate lyase activity; however, mutants deficient in molybdenum cofactor synthesis have an active citrate lyase (Clark, FEMS Microbiol. Lett. 55:245-249 (1990)). The E. coli enzyme is encoded by citEFD and the citrate lyase synthetase is encoded by citC (Nilekani and SivaRaman, Biochemistry 22:4657-4663 (1983)). The Leuconostoc mesenteroides citrate lyase has been cloned, characterized and expressed in E. coli (Bekal et al., J. Bacteriol. 180:647-654 (1998)). Citrate lyase enzymes have also been identified in enterobacteria that utilize citrate as a carbon and energy source, including Salmonella typhimurium and Klebsiella pneumoniae (Bott, Arch. Microbiol. 167: 78-88 (1997); Bott and Dimroth, Mol. Microbiol. 14:347-356 (1994)). The aforementioned proteins are tabulated below.


Protein	GenBank ID	GI Number	Organism

citF	AAC73716.1	1786832	Escherichia coli
Cite	AAC73717.2	87081764	Escherichia coli
citD	AAC73718.1	1786834	Escherichia coli
citC	AAC73719.2	87081765	Escherichia coli
citG	AAC73714.1	1786830	Escherichia coli
citX	AAC73715.1	1786831	Escherichia coli
citF	CAA71633.1	2842397	Leuconostoc mesenteroides
citE	CAA71632.1	2842396	Leuconostoc mesenteroides
citD	CAA71635.1	2842395	Leuconostoc mesenteroides
citC	CAA71636.1	3413797	Leuconostoc mesenteroides
citG	CAA71634.1	2842398	Leuconostoc mesenteroides
citX	CAA71634.1	2842398	Leuconostoc mesenteroides
citF	NP_459613.1	16763998	Salmonella typhimurium
citE	AAL19573.1	16419133	Salmonella typhimurium
citD	NP_459064.1	16763449	Salmonella typhimurium
citC	NP_459616.1	16764001	Salmonella typhimurium
citG	NP_459611.1	16763996	Salmonella typhimurium
citX	NP_459612.1	16763997	Salmonella typhimurium
citF	CAA56217.1	565619	Klebsiella pneumoniae
cite	CAA56216.1	565618	Klebsiella pneumoniae
citD	CAA56215.1	565617	Klebsiella pneumoniae
citC	BAH66541.1	238774045	Klebsiella pneumoniae
citG	CAA56218.1	565620	Klebsiella pneumoniae
citX	AAL60463.1	18140907	Klebsiella pneumoniae

Acetate kinase (EC 2.7.2.1) catalyzes the reversible ATP-dependent phosphorylation of acetate to acetylphosphate. Exemplary acetate kinase enzymes have been characterized in many organisms including E. coli, Clostridium acetobutylicum and Methanosarcina thermophila (Ingram-Smith et al., J. Bacteriol. 187:2386-2394 (2005); Fox and Roseman, J. Biol. Chem. 261:13487-13497 (1986); Winzer et al., Microbioloy 143 (Pt 10):3279-3286 (1997)). Acetate kinase activity has also been demonstrated in the gene product of E. coli purT (Marolewski et al., Biochemistry 33:2531-2537 (1994). Some butyrate kinase enzymes (EC 2.7.2.7), for example buk1 and buk2 from Clostridium acetobutylicum, also accept acetate as a substrate (Hartmanis, M. G., J. Biol. Chem. 262:617-621 (1987)).


Protein	GenBank ID	GI Number	Organism

ackA	NP_416799.1	16130231	Escherichia coli
Ack	AAB18301.1	1491790	Clostridium acetobutylicum
Ack	AAA72042.1	349834	Methanosarcina thermophila
purT	AAC74919.1	1788155	Escherichia coli
buk1	NP_349675	15896326	Clostridium acetobutylicum
buk2	Q97II1	20137415	Clostridium acetobutylicum

The formation of acetyl-CoA from acetylphosphate is catalyzed by phosphotransacetylase (EC 2.3.1.8). The pta gene from E. coli encodes an enzyme that reversibly converts acetyl-CoA into acetyl-phosphate (Suzuki, T., Biochim. Biophys. Acta 191:559-569 (969)). Additional acetyltransferase enzymes have been characterized in Bacillus subtilis (Rado and Hoch, Biochim. Biophys. Acta 321:114-125 (1973), Clostridium kluyveri (Stadtman, E., Methods Enzymol. 1:5896-599 (1955), and Thermotoga maritima (Bock et al., J. Bacteriol. 181:1861-1867 (1999)). This reaction is also catalyzed by some phosphotranbutyrylase enzymes (EC 2.3.1.19) including the ptb gene products from Clostridium acetobutylicum (Wiesenborn et al., App. Environ. Microbiol. 55:317-322 (1989); Walter et al., Gene 134:107-111 (1993)). Additional ptb genes are found in butyrate-producing bacterium L2-50 (Louis et al., J. Bacteriol. 186:2099-2106 (2004) and Bacillus megaterium (Vazquez et al., Curr. Microbiol. 42:345-349 (2001).


Protein	GenBank ID	GI Number	Organism

The acylation of acetate to acetyl-CoA is catalyzed by enzymes with acetyl-CoA synthetase activity. Two enzymes that catalyze this reaction are AMP-forming acetyl-CoA synthetase (EC 6.2.1.1) and ADP-forming acetyl-CoA synthetase (EC 6.2.1.13). AMP-forming acetyl-CoA synthetase (ACS) is the predominant enzyme for activation of acetate to acetyl-CoA. Exemplary ACS enzymes are found in E. coli (Brown et al., J. Gen. Microbiol. 102:327-336 (1977)), Ralstonia eutropha (Priefert and Steinbuchel, J. Bacteriol. 174:6590-6599 (1992)), Methanothermobacter thermautotrophicus (Ingram-Smith and Smith, Archaea 2:95-107 (2007)), Salmonella enterica (Gulick et al., Biochemistry 42:2866-2873 (2003)) and Saccharomyces cerevisiae (Jogl and Tong, Biochemistry 43:1425-1431 (2004)). ADP-forming acetyl-CoA synthetases are reversible enzymes with a generally broad substrate range (Musfeldt and Schonheit, J. Bacteriol. 184:636-644 (2002)). Two isozymes of ADP-forming acetyl-CoA synthetases are encoded in the Archaeoglobus fulgidus genome by are encoded by AF 1211 and AF 1983 (Musfeldt and Schonheit, supra (2002)). The enzyme from Haloarcula marismortui (annotated as a succinyl-CoA synthetase) also accepts acetate as a substrate and reversibility of the enzyme was demonstrated (Brasen and Schonheit, Arch. Microbiol. 182:277-287 (2004)). The ACD encoded by PAE3250 from hyperthermophilic crenarchaeon Pyrobaculum aerophilum showed the broadest substrate range of all characterized ACDs, reacting with acetate, isobutyryl-CoA (preferred substrate) and phenylacetyl-CoA (Brasen and Schonheit, supra (2004)). Directed evolution or engineering can be used to modify this enzyme to operate at the physiological temperature of the host organism. The enzymes from A. fulgidus, H. marismortui and P. aerophilum have all been cloned, functionally expressed, and characterized in E. coli (Brasen and Schonheit, supra (2004); Musfeldt and Schonheit, supra (2002)). Additional candidates include the succinyl-CoA synthetase encoded by sucCD in E. coli (Buck et al., Biochemistry 24:6245-6252 (1985)) and the acyl-CoA ligase from Pseudomonas putida (Fernandez-Valverde et al., Appl. Environ. Microbiol. 59:1149-1154 (1993)). The aforementioned proteins are tabulated below.


Protein	GenBank ID	GI Number	Organism

acs	AAC77039.1	1790505	Escherichia coli
acoE	AAA21945.1	141890	Ralstonia eutropha
acs1	ABC87079.1	86169671	Methanothermobacter thermautotrophicus
acs1	AAL23099.1	16422835	Salmonella enterica
ACS1	Q01574.2	257050994	Saccharomyces cerevisiae
AF1211	NP_070039.1	11498810	Archaeoglobus fulgidus
AF1983	NP_070807.1	11499565	Archaeoglobus fulgidus
scs	YP_135572.1	55377722	Haloarcula marismortui
PAE3250	NP_560604.1	18313937	Pyrobaculum aerophilum str.
			IM2
sucC	NP_415256.1	16128703	Escherichia coli
sucD	AAC73823.1	1786949	Escherichia coli
paaF	AAC24333.2	22711873	Pseudomonas putida

The product yields per C-mol of substrate of microbial cells synthesizing reduced fermentation products such as caprolactone, are limited by insufficient reducing equivalents in the carbohydrate feedstock. Reducing equivalents, or electrons, can be extracted from synthesis gas components such as CO and H₂using carbon monoxide dehydrogenase (CODH) and hydrogenase enzymes, respectively. The reducing equivalents are then passed to acceptors such as oxidized ferredoxins, oxidized quinones, oxidized cytochromes, NAD(P)+, water, or hydrogen peroxide to form reduced ferredoxin, reduced quinones, reduced cytochromes, NAD(P)H, H₂, or water, respectively. Reduced ferredoxin and NAD(P)H are particularly useful as they can serve as redox carriers for various Wood-Ljungdahl pathway and reductive TCA cycle enzymes.
A combined feedstock strategy where syngas is combined with a sugar-based feedstock or other carbon substrate can greatly improve the theoretical yields. In this co-feeding appoach, syngas components H₂and CO can be utilized by the hydrogenase and CO dehydrogenase to generate reducing equivalents, that can be used to power chemical production pathways in which the carbons from sugar or other carbon substrates will be maximally conserved and the theoretical yields improved. In case of caprolactone production from glucose or sugar, the theoretical yields improve from XX mol caprolactone per mol of glucose to YY mol caprolactone per mol of glucose. Such improvements provide environmental and economic benefits and greatly enhance sustainable chemical production.
Herein below the enzymes and the corresponding genes used for extracting redox from synags components are described. CODH is a reversible enzyme that interconverts CO and CO₂at the expense or gain of electrons. The natural physiological role of the CODH in ACS/CODH complexes is to convert CO₂to CO for incorporation into acetyl-CoA by acetyl-CoA synthase. Nevertheless, such CODH enzymes are suitable for the extraction of reducing equivalents from CO due to the reversible nature of such enzymes. Expressing such CODH enzymes in the absence of ACS allows them to operate in the direction opposite to their natural physiological role (i.e., CO oxidation).
In M. thermoacetica, C. hydrogenoformans, C. carboxidivorans P7, and several other organisms, additional CODH encoding genes are located outside of the ACS/CODH operons. These enzymes provide a means for extracting electrons (or reducing equivalents) from the conversion of carbon monoxide to carbon dioxide. The M. thermoacetica gene (Genbank Accession Number: YP_430813) is expressed by itself in an operon and is believed to transfer electrons from CO to an external mediator like ferredoxin in a “Ping-pong” reaction. The reduced mediator then couples to other reduced nicolinamide adenine dinucleotide phosphate (NAD(P)H) carriers or ferredoxin-dependent cellular processes (Ragsdale, Annals of the New York Academy of Sciences 1125: 129-136 (2008)). The genes encoding the C. hydrogenoformans CODH-II and CooF, a neighboring protein, were cloned and sequenced (Gonzalez and Robb, FEMS Microbiol Lett. 191:243-247 (2000)). The resulting complex was membrane-bound, although cytoplasmic fractions of CODH-II were shown to catalyze the formation of NADPH suggesting an anabolic role (Svetlitchnyi et al., J Bacteriol. 183:5134-5144 (2001)). The crystal structure of the CODH-II is also available (Dobbek et al., Science 293:1281-1285 (2001)). Similar ACS-free CODH enzymes can be found in a diverse array of organisms including Geobacter metallireducens GS-15, Chlorobium phaeobacteroides D SM 266, Clostridium cellulolyticum H10, Desulfovibrio desulfuricans subsp. desulfuricans str. ATCC 27774, Pelobacter carbinolicus DSM 2380, and Campylobacter curvus 525.92.


Protein	GenBank ID	GI Number	Organism

CODH (putative)	YP_430813	83590804	Moorella thermoacetica
CODH-II (CooS-II)	YP_358957	78044574	Carboxydothermus
			hydrogenoformans
CooF	YP_358958	78045112	Carboxydothermus
			hydrogenoformans
CODH (putative)	ZP_05390164.1	255523193	Clostridium carboxidivorans
			P7
CcarbDRAFT_0341	ZP_05390341.1	255523371	Clostridium carboxidivorans
			P7
CcarbDRAFT_1756	ZP_05391756.1	255524806	Clostridium carboxidivorans
			P7
CcarbDRAFT_2944	ZP_05392944.1	255526020	Clostridium carboxidivorans
			P7
CODH	YP_384856.1	78223109	Geobacter metallireducens GS-
			15
Cpha266_0148	YP_910642.1	119355998	Chlorobium
(cytochrome c)			phaeobacteroides DSM 266
Cpha266_0149	YP_910643.1	119355999	Chlorobium
(CODH)			phaeobacteroides DSM 266
Ccel_0438	YP_002504800.1	220927891	Clostridium cellulolyticum H10
Ddes_0382	YP_002478973.1	220903661	Desulfovibrio desulfuricans
(CODH)			subsp. desulfuricans str. ATCC
			27774
Ddes_0381 (CooC)	YP_002478972.1	220903660	Desulfovibrio desulfuricans
			subsp. desulfuricans str. ATCC
			27774
Pcar_0057	YP_355490.1	7791767	Pelobacter carbinolicus DSM
(CODH)			2380
Pcar_0058	YP_355491.1	7791766	Pelobacter carbinolicus DSM
(CooC)			2380
Pcar_0058	YP_355492.1	7791765	Pelobacter carbinolicus DSM
(HypA)			2380
CooS (CODH)	YP_001407343.1	154175407	Campylobacter curvus 525.92
CLJU_c09110	ADK13979.1	300434212	Clostridium ljungdahli
CLJU_c09100	ADK13978.1	300434211	Clostridium ljungdahli
CLJU_c09090	ADK13977.1	300434210	Clostridium ljungdahli

In some cases, hydrogenase encoding genes are located adjacent to a CODH. In Rhodospirillum rubrum, the encoded CODH/hydrogenase proteins form a membrane-bound enzyme complex that has been indicated to be a site where energy, in the form of a proton gradient, is generated from the conversion of CO and H₂O to CO₂and H₂(Fox et al., J Bacteriol. 178:6200-6208 (1996)). The CODH-I of C. hydrogenoformans and its adjacent genes have been proposed to catalyze a similar functional role based on their similarity to the R. rubrum CODH/hydrogenase gene cluster (Wu et al., PLoS Genet. 1:e65 (2005)). The C. hydrogenoformans CODH-I was also shown to exhibit intense CO oxidation and CO₂reduction activities when linked to an electrode (Parkin et al., J Am. Chem. Soc. 129:10328-10329 (2007)). The protein sequences of exemplary CODH and hydrogenase genes can be identified by the following GenBank accession numbers.


Protein	GenBank ID	GI Number	Organism

CODH-I	YP_360644	78043418	Carboxydothermus
(CooS-I)			hydrogenoformans
CooF	YP_360645	78044791	Carboxydothermus
			hydrogenoformans
HypA	YP_360646	78044340	Carboxydothermus
			hydrogenoformans
CooH	YP_360647	78043871	Carboxydothermus
			hydrogenoformans
CooU	YP_360648	78044023	Carboxydothermus
			hydrogenoformans
CooX	YP_360649	78043124	Carboxydothermus
			hydrogenoformans
CooL	YP_360650	78043938	Carboxydothermus
			hydrogenoformans
CooK	YP_360651	78044700	Carboxydothermus
			hydrogenoformans
CooM	YP_360652	78043942	Carboxydothermus
			hydrogenoformans
CooC	YP_360654.1	78043296	Carboxydothermus
			hydrogenoformans
CooA-1	YP_360655.1	78044021	Carboxydothermus
			hydrogenoformans
CooL	AAC45118	1515468	Rhodospirillum rubrum
CooX	AAC45119	1515469	Rhodospirillum rubrum
CooU	AAC45120	1515470	Rhodospirillum rubrum
CooH	AAC45121	1498746	Rhodospirillum rubrum
CooF	AAC45122	1498747	Rhodospirillum rubrum
CODH (CooS)	AAC45123	1498748	Rhodospirillum rubrum
CooC	AAC45124	1498749	Rhodospirillum rubrum
CooT	AAC45125	1498750	Rhodospirillum rubrum
CooJ	AAC45126	1498751	Rhodospirillum rubrum

Native to E. coli and other enteric bacteria are multiple genes encoding up to four hydrogenases (Sawers, G., Antonie Van Leeuwenhoek 66:57-88 (1994); Sawers et al., J Bacteriol. 164:1324-1331 (1985); Sawers and Boxer, Eur. J Biochem. 156:265-275 (1986); Sawers et al., J Bacteriol. 168:398-404 (1986)). Given the multiplicity of enzyme activities, E. coli or another host organism can provide sufficient hydrogenase activity to split incoming molecular hydrogen and reduce the corresponding acceptor. E. coli possesses two uptake hydrogenases, Hyd-1 and Hyd-2, encoded by the hyaABCDEF and hybOABCDEFG gene clusters, respectively (Lukey et al., J. Biol. Chem. 285(6):3928-3938 (2010)). Hyd-1 is oxygen-tolerant, irreversible, and is coupled to quinone reduction via the hyaC cytochrome. Hyd-2 is sensitive to 02, reversible, and transfers electrons to the periplasmic ferredoxin hybA which, in turn, reduces a quinone via the hybB integral membrane protein. Reduced quinones can serve as the source of electrons for fumarate reductase in the reductive branch of the TCA cycle. Reduced ferredoxins can be used by enzymes such as NAD(P)H:ferredoxin oxidoreductases to generate NADPH or NADH. They can alternatively be used as the electron donor for reactions such as pyruvate ferredoxin oxidoreductase, AKG ferredoxin oxidoreductase, and 5,10-methylene-H4folate reductase.


Protein	GenBank ID	GI Number	Organism

HyaA	AAC74057.1	1787206	Escherichia coli
HyaB	AAC74058.1	1787207	Escherichia coli
HyaC	AAC74059.1	1787208	Escherichia coli
HyaD	AAC74060.1	1787209	Escherichia coli
HyaE	AAC74061.1	1787210	Escherichia coli
HyaF	AAC74062.1	1787211	Escherichia coli
HybO	AAC76033.1	1789371	Escherichia coli
HybA	AAC76032.1	1789370	Escherichia coli
HybB	AAC76031.1	2367183	Escherichia coli
HybC	AAC76030.1	1789368	Escherichia coli
HybD	AAC76029.1	1789367	Escherichia coli
HybE	AAC76028.1	1789366	Escherichia coli
HybF	AAC76027.1	1789365	Escherichia coli
HybG	AAC76026.1	1789364	Escherichia coli

The hydrogen-lyase systems of E. coli include hydrogenase 3, a membrane-bound enzyme complex using ferredoxin as an acceptor, and hydrogenase 4 that also uses a ferredoxin acceptor. Hydrogenase 3 and 4 are encoded by the hyc and hyfgene clusters, respectively. Hydrogenase 3 has been shown to be a reversible enzyme (Maeda et al., Appl Microbiol Biotechnol 76(5): 1035-42 (2007)). Hydrogenase activity in E. coli is also dependent upon the expression of the hyp genes whose corresponding proteins are involved in the assembly of the hydrogenase complexes (Jacobi et al., Arch. Microbiol 158:444-451 (1992); Rangarajan et al., J. Bacteriol. 190:1447-1458 (2008)).


Protein	GenBank ID	GI Number	Organism

HycA	NP_417205	16130632	Escherichia coli
HycB	NP_417204	16130631	Escherichia coli
HycC	NP_417203	16130630	Escherichia coli
HycD	NP_417202	16130629	Escherichia coli
HycE	NP_417201	16130628	Escherichia coli
HycF	NP_417200	16130627	Escherichia coli
HycG	NP_417199	16130626	Escherichia coli
HycH	NP_417198	16130625	Escherichia coli
HycI	NP_417197	16130624	Escherichia coli
HyfA	NP_416976	90111444	Escherichia coli
HyfB	NP_416977	16130407	Escherichia coli
HyfC	NP_416978	90111445	Escherichia coli
HyfD	NP_416979	16130409	Escherichia coli
HyfE	NP_416980	16130410	Escherichia coli
HyfF	NP_416981	16130411	Escherichia coli
HyfG	NP_416982	16130412	Escherichia coli
HyfH	NP_416983	16130413	Escherichia coli
HyfI	NP_416984	16130414	Escherichia coli
HyfJ	NP_416985	90111446	Escherichia coli
HyfR	NP_416986	90111447	Escherichia coli
HypA	NP_417206	16130633	Escherichia coli
HypB	NP_417207	16130634	Escherichia coli
HypC	NP_417208	16130635	Escherichia coli
HypD	NP_417209	16130636	Escherichia coli
HypE	NP_417210	226524740	Escherichia coli
HypF	NP_417192	16130619	Escherichia coli

The M. thermoacetica hydrogenases are suitable for a host that lacks sufficient endogenous hydrogenase activity. M. thermoacetica can grow with CO₂as the exclusive carbon source indicating that reducing equivalents are extracted from H₂to enable acetyl-CoA synthesis via the Wood-Ljungdahl pathway (Drake, H. L., J. Bacteriol. 150:702-709 (1982); Drake and Daniel, Res. Microbiol. 155:869-883 (2004); Kellum and Drake, J. Bacteriol. 160:466-469 (1984)) (see FIG. 6). M. thermoacetica has homologs to several hyp, hyc, and hyf genes from E. coli. The protein sequences encoded for by these genes are identified by the following GenBank accession numbers.
Proteins in M. thermoacetica whose genes are homologous to the E. coli hyp genes are shown below.


Protein	GenBank ID	GI Number	Organism

Moth_2175	YP_431007	83590998	Moorella thermoacetica
Moth_2176	YP_431008	83590999	Moorella thermoacetica
Moth_2177	YP_431009	83591000	Moorella thermoacetica
Moth_2178	YP_431010	83591001	Moorella thermoacetica
Moth_2179	YP_431011	83591002	Moorella thermoacetica
Moth_2180	YP_431012	83591003	Moorella thermoacetica
Moth_2181	YP_431013	83591004	Moorella thermoacetica

Proteins in M. thermoacetica that are homologous to the E. coli Hydrogenase 3 and/or 4 proteins are listed in the following table.


Protein	GenBank ID	GI Number	Organism

Moth_2182	YP_431014	83591005	Moorella thermoacetica
Moth_2183	YP_431015	83591006	Moorella thermoacetica
Moth_2184	YP_431016	83591007	Moorella thermoacetica
Moth_2185	YP_431017	83591008	Moorella thermoacetica
Moth_2186	YP_431018	83591009	Moorella thermoacetica
Moth_2187	YP_431019	83591010	Moorella thermoacetica
Moth_2188	YP_431020	83591011	Moorella thermoacetica
Moth_2189	YP_431021	83591012	Moorella thermoacetica
Moth_2190	YP_431022	83591013	Moorella thermoacetica
Moth_2191	YP_431023	83591014	Moorella thermoacetica
Moth_2192	YP_431024	83591015	Moorella thermoacetica

In addition, several gene clusters encoding hydrogenase functionality are present in M. thermoacetica and their corresponding protein sequences are provided below.


Protein	GenBank ID	GI Number	Organism

Moth_0439	YP_429313	83589304	Moorella thermoacetica
Moth_0440	YP_429314	83589305	Moorella thermoacetica
Moth_0441	YP_429315	83589306	Moorella thermoacetica
Moth_0442	YP_429316	83589307	Moorella thermoacetica
Moth_0809	YP_429670	83589661	Moorella thermoacetica
Moth_0810	YP_429671	83589662	Moorella thermoacetica
Moth_0811	YP_429672	83589663	Moorella thermoacetica
Moth_0812	YP_429673	83589664	Moorella thermoacetica
Moth_0814	YP_429674	83589665	Moorella thermoacetica
Moth_0815	YP_429675	83589666	Moorella thermoacetica
Moth_0816	YP_429676	83589667	Moorella thermoacetica
Moth_1193	YP_430050	83590041	Moorella thermoacetica
Moth_1194	YP_430051	83590042	Moorella thermoacetica
Moth_1195	YP_430052	83590043	Moorella thermoacetica
Moth_1196	YP_430053	83590044	Moorella thermoacetica
Moth_1717	YP_430562	83590553	Moorella thermoacetica
Moth_1718	YP_430563	83590554	Moorella thermoacetica
Moth_1719	YP_430564	83590555	Moorella thermoacetica
Moth_1883	YP_430726	83590717	Moorella thermoacetica
Moth_1884	YP_430727	83590718	Moorella thermoacetica
Moth_1885	YP_430728	83590719	Moorella thermoacetica
Moth_1886	YP_430729	83590720	Moorella thermoacetica
Moth_1887	YP_430730	83590721	Moorella thermoacetica
Moth_1888	YP_430731	83590722	Moorella thermoacetica
Moth_1452	YP_430305	83590296	Moorella thermoacetica
Moth_1453	YP_430306	83590297	Moorella thermoacetica
Moth_1454	YP_430307	83590298	Moorella thermoacetica

Ralstonia eutropha H16 uses hydrogen as an energy source with oxygen as a terminal electron acceptor. Its membrane-bound uptake [NiFe]-hydrogenase is an “02-tolerant” hydrogenase (Cracknell, et al. Proc Nat Acad Sci, 106(49) 20681-20686 (2009)) that is periplasmically-oriented and connected to the respiratory chain via a b-type cytochrome (Schink and Schlegel, Biochim. Biophys. Acta, 567, 315-324 (1979); Bernhard et al., Eur. J. Biochem. 248, 179-186 (1997)). R. eutropha also contains an 02-tolerant soluble hydrogenase encoded by the Hox operon which is cytoplasmic and directly reduces NAD+ at the expense of hydrogen (Schneider and Schlegel, Biochim. Biophys. Acta 452, 66-80 (1976); Burgdorf, J. Bact. 187(9) 3122-3132(2005)). Soluble hydrogenase enzymes are additionally present in several other organisms including Geobacter sulfurreducens (Coppi, Microbiology 151, 1239-1254 (2005)), Synechocystis str. PCC 6803 (Germer, J. Biol. Chem., 284(52), 36462-36472 (2009)), and Thiocapsa roseopersicina (Rakhely, Appl. Environ. Microbiol. 70(2) 722-728 (2004)). The Synechocystis enzyme is capable of generating NADPH from hydrogen. Overexpression of both the Hox operon from Synechocystis str. PCC 6803 and the accessory genes encoded by the Hyp operon from Nostoc sp. PCC 7120 led to increased hydrogenase activity compared to expression of the Hox genes alone (Germer, J. Biol. Chem. 284(52), 36462-36472 (2009)).


Protein	GenBank ID	GI Number	Organism

HoxF	NP_942727.1	38637753	Ralstonia eutropha H16
HoxU	NP_942728.1	38637754	Ralstonia eutropha H16
HoxY	NP_942729.1	38637755	Ralstonia eutropha H16
HoxH	NP_942730.1	38637756	Ralstonia eutropha H16
HoxW	NP_942731.1	38637757	Ralstonia eutropha H16
HoxI	NP_942732.1	38637758	Ralstonia eutropha H16
HoxE	NP_953767.1	39997816	Geobacter sulfurreducens
HoxF	NP_953766.1	39997815	Geobacter sulfurreducens
HoxU	NP_953765.1	39997814	Geobacter sulfurreducens
HoxY	NP_953764.1	39997813	Geobacter sulfurreducens
HoxH	NP_953763.1	39997812	Geobacter sulfurreducens
GSU2717	NP_953762.1	39997811	Geobacter sulfurreducens
HoxE	NP_441418.1	16330690	Synechocystis str. PCC
			6803
HoxF	NP_441417.1	16330689	Synechocystis str. PCC
			6803
Unknown	NP_441416.1	16330688	Synechocystis str. PCC
function			6803
HoxU	NP_441415.1	16330687	Synechocystis str. PCC
			6803
HoxY	NP_441414.1	16330686	Synechocystis str. PCC
			6803
Unknown	NP_441413.1	16330685	Synechocystis str. PCC
function			6803
Unknown	NP_441412.1	16330684	Synechocystis str. PCC
function			6803
HoxH	NP_441411.1	16330683	Synechocystis str. PCC
			6803
HypF	NP_484737.1	17228189	Nostoc sp. PCC 7120
HypC	NP_484738.1	17228190	Nostoc sp. PCC 7120
HypD	NP_484739.1	17228191	Nostoc sp. PCC 7120
Unknown	NP_484740.1	17228192	Nostoc sp. PCC 7120
function
HypE	NP_484741.1	17228193	Nostoc sp. PCC 7120
HypA	NP_484742.1	17228194	Nostoc sp. PCC 7120
HypB	NP_484743.1	17228195	Nostoc sp. PCC 7120
Hox1E	AAP50519.1	37787351	Thiocapsa roseopersicina
Hox1F	AAP50520.1	37787352	Thiocapsa roseopersicina
Hox1U	AAP50521.1	37787353	Thiocapsa roseopersicina
Hox1Y	AAP50522.1	37787354	Thiocapsa roseopersicina
Hox1H	AAP50523.1	37787355	Thiocapsa roseopersicina

Genes encoding hydrogenase enzymes from C. ljungdahli are shown below.


Protein	GenBank ID	GI Number	Organism

CLJU_c20290	ADK15091.1	300435324	Clostridium ljungdahli
CLJU_c07030	ADK13773.1	300434006	Clostridium ljungdahli
CLJU_c07040	ADK13774.1	300434007	Clostridium ljungdahli
CLJU_c07050	ADK13775.1	300434008	Clostridium ljungdahli
CLJU_c07060	ADK13776.1	300434009	Clostridium ljungdahli
CLJU_c07070	ADK13777.1	300434010	Clostridium ljungdahli
CLJU_c07080	ADK13778.1	300434011	Clostridium ljungdahli
CLJU_c14730	ADK14541.1	300434774	Clostridium ljungdahli
CLJU_c14720	ADK14540.1	300434773	Clostridium ljungdahli
CLJU_c14710	ADK14539.1	300434772	Clostridium ljungdahli
CLJU_c14700	ADK14538.1	300434771	Clostridium ljungdahli
CLJU_c28670	ADK15915.1	300436148	Clostridium ljungdahli
CLJU_c28660	ADK15914.1	300436147	Clostridium ljungdahli
CLJU_c28650	ADK15913.1	300436146	Clostridium ljungdahli
CLJU_c28640	ADK15912.1	300436145	Clostridium ljungdahli

Several enzymes and the corresponding genes used for fixing carbon dioxide to either pyruvate or phosphoenolpyruvate to form the TCA cycle intermediates, oxaloacetate or malate are described below.
Carboxylation of phosphoenolpyruvate to oxaloacetate is catalyzed by phosphoenolpyruvate carboxylase. Exemplary PEP carboxylase enzymes are encoded by ppc in E. coli (Kai et al., Arch. Biochem. Biophys. 414:170-179 (2003), ppcA in Methylobacterium extorquens AM1 (Arps et al., J. Bacteriol. 175:3776-3783 (1993), and ppc in Corynebacterium glutamicum (Eikmanns et al., Mol. Gen. Genet. 218:330-339 (1989).


Protein	GenBank ID	GI Number	Organism

Ppc	NP_418391	16131794	Escherichia coli
ppcA	AAB58883	28572162	Methylobacterium extorquens
Ppc	ABB53270	80973080	Corynebacterium glutamicum

An alternative enzyme for converting phosphoenolpyruvate to oxaloacetate is PEP carboxykinase, which simultaneously forms an ATP while carboxylating PEP. In most organisms PEP carboxykinase serves a gluconeogenic function and converts oxaloacetate to PEP at the expense of one ATP. S. cerevisiae is one such organism whose native PEP carboxykinase, PCK1, serves a gluconeogenic role (Valdes-Hevia et al., FEBS Lett. 258:313-316 (1989). E. coli is another such organism, as the role of PEP carboxykinase in producing oxaloacetate is believed to be minor when compared to PEP carboxylase, which does not form ATP, possibly due to the higher K_mfor bicarbonate of PEP carboxykinase (Kim et al., Appl. Environ. Microbiol. 70:1238-1241 (2004)). Nevertheless, activity of the native E. coli PEP carboxykinase from PEP towards oxaloacetate has been recently demonstrated in ppc mutants of E. coli K-12 (Kwon et al., J. Microbiol. Biotechnol. 16:1448-1452 (2006)). These strains exhibited no growth defects and had increased succinate production at high NaHCO₃concentrations. Mutant strains of E. coli can adopt Pck as the dominant CO2-fixing enzyme following adaptive evolution (Zhang et al. 2009). In some organisms, particularly rumen bacteria, PEP carboxykinase is quite efficient in producing oxaloacetate from PEP and generating ATP. Examples of PEP carboxykinase genes that have been cloned into E. coli include those from Mannheimia succiniciproducens (Lee et al., Biotechnol. Bioprocess Eng. 7:95-99 (2002)), Anaerobiospirillum succiniciproducens (Laivenieks et al., Appl. Environ. Microbiol. 63:2273-2280 (1997), and Actinobacillus succinogenes (Kim et al. supra). The PEP carboxykinase enzyme encoded by Haemophilus influenza is effective at forming oxaloacetate from PEP.


Protein	GenBank ID	GI Number	Organism

PCK1	NP_013023	6322950	Saccharomyces cerevisiae
pck	NP_417862.1	16131280	Escherichia coli
pckA	YP_089485.1	52426348	Mannheimia succiniciproducens
pckA	O09460.1	3122621	Anaerobiospirillum
			succiniciproducens
pckA	Q6W6X5	75440571	Actinobacillus succinogenes
pckA	P43923.1	1172573	Haemophilus influenza

Pyruvate carboxylase (EC 6.4.1.1) directly converts pyruvate to oxaloacetate at the cost of one ATP. Pyruvate carboxylase enzymes are encoded by PYC1 (Walker et al., Biochem. Biophys. Res. Commun. 176:1210-1217 (1991) and PYC2 (Walker et al., supra) in Saccharomyces cerevisiae, and pyc in Mycobacterium smegmatis (Mukhopadhyay and Purwantini, Biochim. Biophys. Acta 1475:191-206 (2000)).


Protein	GenBank ID	GI Number	Organism

PYC1	NP_011453	6321376	Saccharomyces cerevisiae
PYC2	NP_009777	6319695	Saccharomyces cerevisiae
Pyc	YP_890857.1	118470447	Mycobacterium smegmatis

Malic enzyme can be applied to convert CO₂and pyruvate to malate at the expense of one reducing equivalent. Malic enzymes for this purpose can include, without limitation, malic enzyme (NAD-dependent) and malic enzyme (NADP-dependent). For example, one of the E. coli malic enzymes (Takeo, J. Biochem. 66:379-387 (1969)) or a similar enzyme with higher activity can be expressed to enable the conversion of pyruvate and CO₂to malate. By fixing carbon to pyruvate as opposed to PEP, malic enzyme allows the high-energy phosphate bond from PEP to be conserved by pyruvate kinase whereby ATP is generated in the formation of pyruvate or by the phosphotransferase system for glucose transport. Although malic enzyme is typically assumed to operate in the direction of pyruvate formation from malate, overexpression of the NAD-dependent enzyme, encoded by maeA, has been demonstrated to increase succinate production in E. coli while restoring the lethal Δpfl-ΔldhA phenotype under anaerobic conditions by operating in the carbon-fixing direction (Stols and Donnelly, Appl. Environ. Microbiol. 63(7) 2695-2701 (1997)). A similar observation was made upon overexpressing the malic enzyme from Ascaris suum in E. coli (Stols et al., Appl. Biochem. Biotechnol. 63-65(1), 153-158 (1997)). The second E. coli malic enzyme, encoded by maeB, is NADP-dependent and also decarboxylates oxaloacetate and other alpha-keto acids (Iwakura et al., J. Biochem. 85(5):1355-65 (1979)).


Protein	GenBank ID	GI Number	Organism

maeA	NP_415996	90111281	Escherichia coli
maeB	NP_416958	16130388	Escherichia coli
NAD-ME	P27443	126732	Ascaris suum

The enzymes used for converting oxaloacetate (formed from, for example, PEP carboxylase, PEP carboxykinase, or pyruvate carboxylase) or malate (formed from, for example, malic enzyme or malate dehydrogenase) to succinyl-CoA via the reductive branch of the TCA cycle are malate dehydrogenase, fumarate dehydratase (fumarase), fumarate reductase, and succinyl-CoA transferase. The genes for each of the enzymes are described herein above.
Enzymes, genes and methods for engineering pathways from succinyl-CoA to various products into a microorganism are now known in the art. The additional reducing equivalents obtained from CO and/or H₂, as disclosed herein, improve the yields of caprolactone when utilizing carbohydrate-based feedstock. For example, caprolactone can be produced from succinyl-CoA via conversion of adipyl-CoA to caprolactone. Exemplary enzymes for the conversion succinyl-CoA to caprolactone include an adipyl-CoA reductase, an adipate semialdehyde reductase, a 6-hydroxyhexanoyl-CoA transferase, a 6-hydroxyhexanoyl-CoA synthetase, a 6-hydroxyhexanoyl-CoA cyclase, an adipate reductase, a 6-hydroxyhexanoate cyclase, a 6-hydroxyhexanoate kinase, and/or a 6-hydroxyhexanoyl phosphate cyclase (see FIG. 1 steps A/B/C/D; A/B/H/I; A/B/G; E/B/C/D; E/B/H/I; or E/B/G).

Example III

Methods for Handling CO and Anaerobic Cultures

This example describes methods used in handling CO and anaerobic cultures.
A. Handling of CO in Small Quantities for Assays and Small Cultures.
CO is an odorless, colorless and tasteless gas that is a poison. Therefore, cultures and assays that utilized CO required special handling. Several assays, including CO oxidation, acetyl-CoA synthesis, CO concentration using myoglobin, and CO tolerance/utilization in small batch cultures, called for small quantities of the CO gas that were dispensed and handled within a fume hood. Biochemical assays called for saturating very small quantities (<2 mL) of the biochemical assay medium or buffer with CO and then performing the assay. All of the CO handling steps were performed in a fume hood with the sash set at the proper height and blower turned on; CO was dispensed from a compressed gas cylinder and the regulator connected to a Schlenk line. The latter ensures that equal concentrations of CO were dispensed to each of several possible cuvettes or vials. The Schlenk line was set up containing an oxygen scrubber on the input side and an oil pressure release bubbler and vent on the other side. Assay cuvettes were both anaerobic and CO-containing. Therefore, the assay cuvettes were tightly sealed with a rubber stopper and reagents were added or removed using gas-tight needles and syringes. Secondly, small (˜50 mL) cultures were grown with saturating CO in tightly stoppered serum bottles. As with the biochemical assays, the CO-saturated microbial cultures were equilibrated in the fume hood using the Schlenk line setup. Both the biochemical assays and microbial cultures were in portable, sealed containers and in small volumes making for safe handling outside of the fume hood. The compressed CO tank was adjacent to the fume hood.
Typically, a Schlenk line was used to dispense CO to cuvettes, each vented. Rubber stoppers on the cuvettes were pierced with 19 or 20 gage disposable syringe needles and were vented with the same. An oil bubbler was used with a CO tank and oxygen scrubber. The glass or quartz spectrophotometer cuvettes have a circular hole on top into which a Kontes stopper sleeve, Sz7 774250-0007 was fitted. The CO detector unit was positioned proximal to the fume hood.
B. Handling of CO in Larger Quantities Fed to Large-Scale Cultures.
Fermentation cultures are fed either CO or a mixture of CO and H₂to simulate syngas as a feedstock in fermentative production. Therefore, quantities of cells ranging from 1 liter to several liters can include the addition of CO gas to increase the dissolved concentration of CO in the medium. In these circumstances, fairly large and continuously administered quantities of CO gas are added to the cultures. At different points, the cultures are harvested or samples removed. Alternatively, cells are harvested with an integrated continuous flow centrifuge that is part of the fermenter.
The fermentative processes are carried out under anaerobic conditions. In some cases, it is uneconomical to pump oxygen or air into fermenters to ensure adequate oxygen saturation to provide a respiratory environment. In addition, the reducing power generated during anaerobic fermentation may be needed in product formation rather than respiration. Furthermore, many of the enzymes for various pathways are oxygen-sensitive to varying degrees. Classic acetogens such as M. thermoacetica are obligate anaerobes and the enzymes in the Wood-Ljungdahl pathway are highly sensitive to irreversible inactivation by molecular oxygen. While there are oxygen-tolerant acetogens, the repertoire of enzymes in the Wood-Ljungdahl pathway might be incompatible in the presence of oxygen because most are metallo-enzymes, key components are ferredoxins, and regulation can divert metabolism away from the Wood-Ljungdahl pathway to maximize energy acquisition. At the same time, cells in culture act as oxygen scavengers that moderate the need for extreme measures in the presence of large cell growth.
C. Anaerobic Chamber and Conditions.
Exemplary anaerobic chambers are available commercially (see, for example, Vacuum Atmospheres Company, Hawthorne Calif.; MBraun, Newburyport Mass.). Conditions included an O₂concentration of 1 ppm or less and 1 atm pure N₂. In one example, 3 oxygen scrubbers/catalyst regenerators were used, and the chamber included an O₂electrode (such as Teledyne; City of Industry CA). Nearly all items and reagents were cycled four times in the airlock of the chamber prior to opening the inner chamber door. Reagents with a volume >5 mL were sparged with pure N₂prior to introduction into the chamber. Gloves are changed twice/yr and the catalyst containers were regenerated periodically when the chamber displays increasingly sluggish response to changes in oxygen levels. The chamber's pressure was controlled through one-way valves activated by solenoids. This feature allowed setting the chamber pressure at a level higher than the surroundings to allow transfer of very small tubes through the purge valve.
The anaerobic chambers achieved levels of O₂that were consistently very low and were needed for highly oxygen sensitive anaerobic conditions. However, growth and handling of cells does not usually require such precautions. In an alternative anaerobic chamber configuration, platinum or palladium can be used as a catalyst that requires some hydrogen gas in the mix. Instead of using solenoid valves, pressure release can be controlled by a bubbler. Instead of using instrument-based O₂monitoring, test strips can be used instead.
D. Anaerobic Microbiology.
Small cultures were handled as described above for CO handling. In particular, serum or media bottles are fitted with thick rubber stoppers and aluminum crimps are employed to seal the bottle. Medium, such as Terrific Broth, is made in a conventional manner and dispensed to an appropriately sized serum bottle. The bottles are sparged with nitrogen for ˜30 min of moderate bubbling. This removes most of the oxygen from the medium and, after this step, each bottle is capped with a rubber stopper (such as Bellco 20 mm septum stoppers; Bellco, Vineland, N.J.) and crimp-sealed (Bellco 20 mm). Then the bottles of medium are autoclaved using a slow (liquid) exhaust cycle. At least sometimes a needle can be poked through the stopper to provide exhaust during autoclaving; the needle needs to be removed immediately upon removal from the autoclave. The sterile medium has the remaining medium components, for example buffer or antibiotics, added via syringe and needle. Prior to addition of reducing agents, the bottles are equilibrated for 30-60 minutes with nitrogen (or CO depending upon use). A reducing agent such as a 100×150 mM sodium sulfide, 200 mM cysteine-HCl is added. This is made by weighing the sodium sulfide into a dry beaker and the cysteine into a serum bottle, bringing both into the anaerobic chamber, dissolving the sodium sulfide into anaerobic water, then adding this to the cysteine in the serum bottle. The bottle is stoppered immediately as the sodium sulfide solution generates hydrogen sulfide gas upon contact with the cysteine. When injecting into the culture, a syringe filter is used to sterilize the solution. Other components are added through syringe needles, such as B12 (10 μM cyanocobalamin), nickel chloride (NiCl₂, 20 microM final concentration from a 40 mM stock made in anaerobic water in the chamber and sterilized by autoclaving or by using a syringe filter upon injection into the culture), and ferrous ammonium sulfate (final concentration needed is 100 μM-made as 100-1000× stock solution in anaerobic water in the chamber and sterilized by autoclaving or by using a syringe filter upon injection into the culture). To facilitate faster growth under anaerobic conditions, the 1 liter bottles were inoculated with 50 mL of a preculture grown anaerobically. Induction of the pA1-lacO1 promoter in the vectors was performed by addition of isopropyl 3-D-1-thiogalactopyranoside (IPTG) to a final concentration of 0.2 mM and was carried out for about 3 hrs.
Large cultures can be grown in larger bottles using continuous gas addition while bubbling. A rubber stopper with a metal bubbler is placed in the bottle after medium addition and sparged with nitrogen for 30 minutes or more prior to setting up the rest of the bottle. Each bottle is put together such that a sterile filter will sterilize the gas bubbled in and the hoses on the bottles are compressible with small C clamps. Medium and cells are stirred with magnetic stir bars. Once all medium components and cells are added, the bottles are incubated in an incubator in room air but with continuous nitrogen sparging into the bottles.

Example IV

CO Oxidation (CODH) Assay

This example describes assay methods for measuring CO oxidation (CO dehydrogenase; CODH).
The 7 gene CODH/ACS operon of Moorella thermoacetica was cloned into E. coli expression vectors. The intact ˜10 kbp DNA fragment was cloned, and it is likely that some of the genes in this region are expressed from their own endogenous promoters and all contain endogenous ribosomal binding sites. These clones were assayed for CO oxidation, using an assay that quantitatively measures CODH activity. Antisera to the M. thermoacetica gene products was used for Western blots to estimate specific activity. M. thermoacetica is Gram positive, and ribosome binding site elements are expected to work well in E. coli. This activity, described below in more detail, was estimated to be ˜ 1/50th of the M. thermoacetica specific activity. It is possible that CODH activity of recombinant E. coli cells could be limited by the fact that M. thermoacetica enzymes have temperature optima around 55° C. Therefore, a mesophilic CODH/ACS pathway could be advantageous such as the close relative of Moorella that is mesophilic and does have an apparently intact CODH/ACS operon and a Wood-Ljungdahl pathway, Desulfitobacterium hafniense. Acetogens as potential host organisms include, but are not limited to, Rhodospirillum rubrum, Moorella thermoacetica and Desulfitobacterium hafniense.
CO oxidation is both the most sensitive and most robust of the CODH/ACS assays. It is likely that an E. coli-based syngas using system will ultimately need to be about as anaerobic as Clostridial (i.e., Moorella) systems, especially for maximal activity. Improvement in CODH should be possible but will ultimately be limited by the solubility of CO gas in water.
Initially, each of the genes was cloned individually into expression vectors. Combined expression units for multiple subunits/1 complex were generated. Expression in E. coli at the protein level was determined. Both combined M. thermoacetica CODH/ACS operons and individual expression clones were made.
CO oxidation assay. This assay is one of the simpler, reliable, and more versatile assays of enzymatic activities within the Wood-Ljungdahl pathway and tests CODH (Seravalli et al., Biochemistry 43:3944-3955 (2004)). A typical activity of M. thermoacetica CODH specific activity is 500 U at 55° C. or ˜60 U at 25° C. This assay employs reduction of methyl viologen in the presence of CO. This is measured at 578 nm in stoppered, anaerobic, glass cuvettes.
In more detail, glass rubber stoppered cuvettes were prepared after first washing the cuvette four times in deionized water and one time with acetone. A small amount of vacuum grease was smeared on the top of the rubber gasket. The cuvette was gassed with CO, dried 10 min with a 22 Ga. needle plus an exhaust needle. A volume of 0.98 mlL of reaction buffer (50 mM Hepes, pH 8.5, 2 mM dithiothreitol (DTT) was added using a 22 Ga. needle, with exhaust needled, and 100% CO. Methyl viologen (CH₃viologen) stock was 1 M in water. Each assay used 20 microliters for 20 mM final concentration. When methyl viologen was added, an 18 Ga needle (partial) was used as a jacket to facilitate use of a Hamilton syringe to withdraw the CH₃viologen. 4-5 aliquots were drawn up and discarded to wash and gas equilibrate the syringe. A small amount of sodium dithionite (0.1 M stock) was added when making up the CH₃viologen stock to slightly reduce the CH₃viologen. The temperature was equilibrated to 55° C. in a heated Olis spectrophotometer (Bogart Ga.). A blank reaction (CH₃viologen+buffer) was run first to measure the base rate of CH₃viologen reduction. Crude E. coli cell extracts of ACS90 and ACS91 (CODH-ACS operon of M. thermoacetica with and without, respectively, the first cooC). 10 microliters of extract were added at a time, mixed and assayed. Reduced CH₃viologen turns purple. The results of an assay are shown in Table I.

TABLE I

Crude extract CO Oxidation Activities.

ACS90	7.7 mg/ml	ACS91	11.8 mg/ml
Mta98	9.8 mg/ml	Mta99	11.2 mg/ml

Extract	Vol	OD/	U/ml	U/mg

ACS90	10 microliters	0.073	0.376	0.049
ACS91	10 microliters	0.096	0.494	0.042
Mta99	10 microliters	0.0031	0.016	0.0014
ACS90	10 microliters	0.099	0.51	0.066
Mta99	25 microliters	0.012	0.025	0.0022
ACS91	25 microliters	0.215	0.443	0.037
Mta98	25 microliters	0.019	0.039	0.004
ACS91	10 microliters	0.129	0.66	0.056

Averages
ACS90 0.057 U/mg
ACS91 0.045 U/mg
Mta99 0.0018 U/mg

Mta98/Mta99 are E. coli MG1655 strains that express methanol methyltransferase genes from M. thermoacetia and, therefore, are negative controls for the ACS90 ACS91 E. coli strains that contain M. thermoacetica CODH operons.
If −1% of the cellular protein is CODH, then these figures would be approximately 100× less than the 500 U/mg activity of pure M. thermoacetica CODH. Actual estimates based on Western blots are 0.5% of the cellular protein, so the activity is about 50× less than for M. thermoacetica CODH. Nevertheless, this experiment demonstrates CO oxidation activity in recombinant E. coli with a much smaller amount in the negative controls. The small amount of CO oxidation (CH₃viologen reduction) seen in the negative controls indicates that E. coli may have a limited ability to reduce CH₃viologen.
To estimate the final concentrations of CODH and Mtr proteins, SDS-PAGE followed by Western blot analyses were performed on the same cell extracts used in the CO oxidation, ACS, methyltransferase, and corrinoid Fe—S assays. The antisera used were polyclonal to purified M. thermoacetica CODH-ACS and Mtr proteins and were visualized using an alkaline phosphatase-linked goat-anti-rabbit secondary antibody. The Westerns were performed and results are shown in FIG. 8. The amounts of CODH in ACS90 and ACS91 were estimated at 50 ng by comparison to the control lanes. Expression of CODH-ACS operon genes including 2 CODH subunits and the methyltransferase were confirmed via Western blot analysis. Therefore, the recombinant E. coli cells express multiple components of a 7 gene operon. In addition, both the methyltransferase and corrinoid iron sulfur protein were active in the same recombinant E. coli cells. These proteins are part of the same operon cloned into the same cells.
The CO oxidation assays were repeated using extracts of Moorella thermoacetica cells for the positive controls. Though CODH activity in E. coli ACS90 and ACS91 was measurable, it was at about 130-150× lower than the M. thermoacetica control. The results of the assay are shown in FIG. 9. Briefly, cells (M. thermoacetica or E. coli with the CODH/ACS operon; ACS90 or ACS91 or empty vector: pZA33S) were grown and extracts prepared as described herein. Assays were performed as described above at 55° C. at various times on the day the extracts were prepared. Reduction of methylviologen was followed at 578 nm over a 120 sec time course.
These results describe the CO oxidation (CODH) assay and results. Recombinant E. coli cells expressed CO oxidation activity as measured by the methyl viologen reduction assay.

Example V

E. coli CO Tolerance Experiment and CO Concentration Assay (Myoglobin Assay)

This example describes the tolerance of E. coli for high concentrations of CO.
To test whether or not E. coli can grow anaerobically in the presence of saturating amounts of CO, cultures were set up in 120 ml serum bottles with 50 ml of Terrific Broth medium (plus reducing solution, NiCl₂, Fe(II)NH₄SO₄, cyanocobalamin, IPTG, and chloramphenicol) as described above for anaerobic microbiology in small volumes. One half of these bottles were equilibrated with nitrogen gas for 30 min. and one half was equilibrated with CO gas for 30 min. An empty vector (pZA33) was used as a control, and cultures containing the pZA33 empty vector as well as both ACS90 and ACS91 were tested with both N₂and CO. All were inoculated and grown for 36 hrs with shaking (250 rpm) at 37° C. At the end of the 36 hour period, examination of the flasks showed high amounts of growth in all. The bulk of the observed growth occurred overnight with a long lag.
Given that all cultures appeared to grow well in the presence of CO, the final CO concentrations were confirmed. This was performed using an assay of the spectral shift of myoglobin upon exposure to CO. Myoglobin reduced with sodium dithionite has an absorbance peak at 435 nm; this peak is shifted to 423 nm with CO. Due to the low wavelength and need to record a whole spectrum from 300 nm on upwards, quartz cuvettes must be used. CO concentration is measured against a standard curve and depends upon the Henry's Law constant for CO of maximum water solubility=970 micromolar at 20° C. and 1 atm.
For the myoglobin test of CO concentration, cuvettes were washed 10× with water, 1× with acetone, and then stoppered as with the CODH assay. N₂was blown into the cuvettes for ˜10 min. A volume of 1 ml of anaerobic buffer (HEPES, pH 8.0, 2 mM DTT) was added to the blank (not equilibrated with CO) with a Hamilton syringe. A volume of 10 microliter myoglobin (˜1 mM—can be varied, just need a fairly large amount) and 1 microliter dithionite (20 mM stock) were added. A CO standard curve was made using CO saturated buffer added at 1 microliter increments. Peak height and shift was recorded for each increment. The cultures tested were pZA33/CO, ACS90/CO, and ACS91/CO. Each of these was added in 1 microliter increments to the same cuvette. Midway through the experiment a second cuvette was set up and used. The results are shown in Table II.

TABLE II

Carbon Monoxide Concentrations, 36 hrs.

Strain and Growth Conditions	Final CO concentration (micromolar)

pZA33-CO	930
ACS90-CO	638
	494
	734
	883
ave	687
SD	164
ACS91-CO	728
	812
	760
	611
ave.	728
SD	85

The results shown in Table II indicate that the cultures grew whether or not a strain was cultured in the presence of CO or not. These results indicate that E. coli can tolerate exposure to CO under anaerobic conditions and that E. coli cells expressing the CODH-ACS operon can metabolize some of the CO.
These results demonstrate that E. coli cells, whether expressing CODH/ACS or not, were able to grow in the presence of saturating amounts of CO. Furthermore, these grew equally well as the controls in nitrogen in place of CO. This experiment demonstrated that laboratory strains of E. coli are insensitive to CO at the levels achievable in a syngas project performed at normal atmospheric pressure. In addition, preliminary experiments indicated that the recombinant E. coli cells expressing CODH/ACS actually consumed some CO, probably by oxidation to carbon dioxide.
Throughout this application various publications have been referenced. The disclosures of these publications in their entireties, including GenBank and GI number publications, are hereby incorporated by reference in this application in order to more fully describe the state of the art to which this invention pertains. Although the invention has been described with reference to the examples provided above, it should be understood that various modifications can be made without departing from the spirit of the invention.

Claims

1. A non-naturally occurring microbial organism, said microbial organism having a caprolactone pathway and comprising at least one exogenous nucleic acid encoding a caprolactone pathway enzyme expressed in a sufficient amount to produce caprolactone, wherein said caprolactone pathway comprises a pathway selected from:

(1) 1D, 1A, 1B, and 1C;

(2) 1E, 1B, 1C and 1D;

(3) 1F, 1A, 1B, 1C and 1D;

(4) 1F, 1E, 1B, 1C and 1D;

(5) 1A, 1B and 1G;

(6) 1E, 1B and 1G;

(7) 1F, 1A, 1B and 1G;

(8) 1F, 1E, 1B and 1G;

(9) 1A, 1B, 1C, 1J and 1I;

(10) 1E, 1B, 1C, 1J and 1I;

(11) 1F, 1A, 1B, 1C, 1J and 1I;

(12) 1F, 1E, 1B, 1C, 1J and 1I;

(13) 1A, 1B, 1H and 1I;

(14) 1E, 1B, 1H and 1I;

(15) 1F, 1A, 1B, 1H and 1I;

(16) 1F, 1E, 1B, 1H and 1I;

(17) 2A, 2B, 2C, 2D, 2E and 2F;

(18) 2A, 2B, 2C, 2D and 2G;

(19) 2A, 2B, 2C, 2D, 2E, 2J and 2I;

(20) 2A, 2B, 2C, 2D, 2H and 2I;

(21) 4A, 4B, 4C, 4D and 3A; and

(22) 5A, 5B, 5C an 3A,

wherein 1A is an adipyl-CoA reductase, wherein 1B is an adipate semialdehyde reductase, wherein 1C is a 6-hydroxyhexanoyl-CoA transferase or a 6-hydroxyhexanoyl-CoA synthetase, wherein 1D is a 6-hydroxyhexanoyl-CoA cyclase or spontaneous cyclization, wherein 1E is an adipate reductase, wherein 1F is an adipyl-CoA transferase, an adipyl-CoA synthetase or an adipyl-CoA hydrolase, wherein 1G is a 6-hydroxyhexanoate cyclase, wherein 1H is a 6-hydroxyhexanoate kinase, wherein 11 is a 6-hydroxyhexanoyl phosphate cyclase or spontaneous cyclization, wherein 1J is a phosphotrans-6-hydroxyhexanoylase, wherein 2A is a 4-hydroxybutyryl-CoA:acetyl-CoA acyltransferase, wherein 2B is a 3-oxo-6-hydroxyhexanoyl-CoA reductase, wherein 2C is a 3,6-dihydroxyhexanoyl-CoA dehydratase, wherein 2D is a 6-hydroxyhex-2-enoyl-CoA reductase, wherein 2E is a 6-hydroxyhexanoyl-CoA transferase, a 6-hydroxyhexanoyl-CoA synthetase or a 6-hydroxyhexanoyl-CoA hydrolase, wherein 2F is a 6-hydroxyhexanoate cyclase, wherein 2G is a 6-hydroxyhexanoyl-CoA cyclase or spontaneous cyclization, wherein 2H is a phosphotrans-6-hydroxyhexanoylase, wherein 2I is a 6-hydroxyhexanoyl phosphate cyclase or spontaneous cyclization, wherein 2J is a 6-hydroxyhexanoate kinase, wherein 3A is a cyclohexanone monooxygenase, wherein 4A is an adipate semialdehyde dehydratase, wherein 4B is a cyclohexane-1,2-dione reductase, wherein 4C is a 2-hydroxycyclohexanone reductase, wherein 4D is a cyclohexane-1,2-diol dehydratase, wherein 5A is a 2-ketocyclohexane-1-carboxoyl-CoA hydrolase (acting on C—C), wherein 5B is a 2-ketocyclohexane-1-carboxoyl-CoA transferase, a 2-ketocyclohexane-1-carboxoyl-CoA synthetase or a 2-ketocyclohexane-1-carboxoyl-CoA hydrolase, and wherein 5C is a 2-ketocyclohexane-1-carboxylate decarboxylase.

2. The non-naturally occurring microbial organism of claim 1, wherein said microbial organism comprises two, three, four, five, six or seven exogenous nucleic acids each encoding a caprolactone pathway enzyme.

3. The non-naturally occurring microbial organism of claim 2, wherein said microbial organism comprises exogenous nucleic acids encoding each of the enzymes of at least one of the pathways selected from (1)-(22).

4. The non-naturally occurring microbial organism of claim 1, wherein said at least one exogenous nucleic acid is a heterologous nucleic acid.

5. The non-naturally occurring microbial organism of claim 1, wherein said non-naturally occurring microbial organism is in a substantially anaerobic culture medium.

6. The non-naturally occurring microbial organism of claim 1, further comprising:

(i) a reductive TCA pathway comprising at least one exogenous nucleic acid encoding a reductive TCA pathway enzyme, wherein said at least one exogenous nucleic acid is selected from an ATP-citrate lyase, citrate lyase, a citryl-CoA synthetase, a citryl-CoA, a fumarate reductase, and an alpha-ketoglutarate:ferredoxin oxidoreductase;

(ii) a reductive TCA pathway comprising at least one exogenous nucleic acid encoding a reductive TCA pathway enzyme, wherein said at least one exogenous nucleic acid is selected from a pyruvate:ferredoxin oxidoreductase, a phosphoenolpyruvate carboxylase, a phosphoenolpyruvate carboxykinase, a CO dehydrogenase, and an H₂hydrogenase; or

(iii) at least one exogenous nucleic acid encodes an enzyme selected from a CO dehydrogenase, an H₂hydrogenase, and combinations thereof.

7. The non-naturally occurring microbial organism of claim 5, wherein said microbial organism comprising (i) further comprises an exogenous nucleic acid encoding an enzyme selected from a pyruvate:ferredoxin oxidoreductase, an aconitase, an isocitrate dehydrogenase, a succinyl-CoA synthetase, a succinyl-CoA transferase, a fumarase, a malate dehydrogenase, an acetate kinase, a phosphotransacetylase, an acetyl-CoA synthetase, an NAD(P)H:ferredoxin oxidoreductase, ferredoxin, and combinations thereof.

8. The non-naturally occurring microbial organism of claim 5, wherein said microbial organism comprising (ii) further comprises an exogenous nucleic acid encoding an enzyme selected from an aconitase, an isocitrate dehydrogenase, a succinyl-CoA synthetase, a succinyl-CoA transferase, a fumarase, a malate dehydrogenase, and combinations thereof.

9. The non-naturally occurring microbial organism of claim 5, wherein said microbial organism comprising (i) comprises three exogenous nucleic acids encoding an ATP-citrate lyase or a citrate lyase, a fumarate reductase, and an alpha-ketoglutarate:ferredoxin oxidoreductase;

wherein said microbial organism comprising (ii) comprises five exogenous nucleic acids encoding a pyruvate:ferredoxin oxidoreductase, a phosphoenolpyruvate carboxylase, a phosphoenolpyruvate carboxykinase, a CO dehydrogenase, and an H₂hydrogenase; or

wherein said microbial organism comprising (iii) comprises two exogenous nucleic acids encoding a CO dehydrogenase and an H₂hydrogenase.

10. A method for producing caprolactone, comprising culturing the non-naturally occurring microbial organism of claim 1 under conditions and for a sufficient period of time to produce caprolactone.

11. Culture medium comprising bioderived caprolactone, wherein said bioderived caprolactone has a carbon-12, carbon-13 and carbon-14 isotope ratio that reflects an atmospheric carbon dioxide uptake source.

12. The culture medium of claim 11, wherein said culture medium is separated from a non-naturally occurring microbial organism having a caprolactone pathway.

13. Bioderived caprolactone having a carbon-12, carbon-13 and carbon-14 isotope ratio that reflects an atmospheric carbon dioxide uptake source.

14. The bioderived caprolactone of claim 13, wherein said bioderived caprolactone has an Fm value of at least 80%, at least 85%, at least 90%, at least 95% or at least 98%.

15. A composition comprising said bioderived caprolactone of claim 13 and a compound other than said bioderived caprolactone.

16. The composition of claim 15, wherein said compound other than said bioderived caprolactone is a trace amount of a cellular portion of a non-naturally occurring microbial organism having a caprolactone pathway.

17. (canceled)

18. A biobased polymer comprising said bioderived caprolactone of claim 13.

19.-20. (canceled)

21. A biobased resin comprising said bioderived caprolactone of claim 13.

22. (canceled)

23. A molded product obtained by molding a biobased polymer or resin of claim 18.

24. (canceled)

25. A process for producing a biobased polymer or resin of claim 18 comprising chemically reacting said bioderived caprolactone with itself or another compound in a polymer producing or a resin producting reaction.