Search Results (555)

Due to environmental pollution and the depletion of fossil fuels, there is growing interest in the development and use of biofuels as environmentally friendly alternatives. One of the most promising biofuels is biohydrogen, hydrogen produced through sustainable processes using microorganisms such as bacteria and algae. One of the most interesting bacteria for hydrogen production is Ralstonia eutropha H16, known for its ability to produce oxygen-tolerant hydrogenases. These enzymes play a crucial role in biohydrogen metabolism and production. The aim of this work was to determine the optimal conditions (reactor type and synthetic medium composition) for the cultivation of R. eutropha H16. The culture media contained different concentrations of fructose and glycerol (mono- or double-substrate cultivation) and the experiments were carried out in a batch reactor. The initial experiments were carried out with 4 g/L fructose or glycerol in the culture medium at pH 7, T = 30 °C, and 120 rpm. The mathematical model, consisting of the growth kinetics (described by the Monod’s model) and the corresponding mass balances, was proposed. The developed model was validated using two independent experiments with different initial substrate concentrations: 2 g/L glycerol and fructose in one medium and 4 g/L fructose and 1 g/L glycerol in the second. In order to propose the optimal cultivation procedure for future research, the mathematical model simulations were performed for different reactor types (batch, fed-batch, and continuous stirred tank reactors) and different initial substrate concentrations. The most successful experiment was the one with 4 g/L glycerol, where γ_X = 0.485 ± 0.001 g/L of biomass was achieved. Further calculations showed that the most biomass would be produced at higher glycerol concentrations (at γ_G = 6.358 g/L, γ_X = 1.311 g/L should be achieved after 200 h of cultivation) and when using a fed-batch reactor (γ_X = 0.944 g/L after 200 h of cultivation). Full article

This paper presents an effective hybrid metaheuristic algorithm combining the genetic algorithm (GA) and a simple algorithm based on evolutionary computation. The evolutionary approach (EA) is applied to form the initial population of the GA, thus improving the algorithm’s performance, especially its convergence speed. To assess its effectiveness, the proposed hybrid algorithm, the EAGA, is evaluated on selected benchmark functions, as well as on a real optimisation process. The EAGA is used to identify parameters in a nonlinear system of differential equations modelling an E. coli fed-batch fermentation process. The obtained results are compared against published results from hybrid metaheuristic algorithms applied to the selected optimisation problems. The EAGA hybrid outperforms the competing algorithms due to its effective initial population generation strategy. The risk of premature convergence is reduced. Better numerical outcomes are achieved. The investigations validate the potential of the proposed hybrid metaheuristic EAGA for solving real complex nonlinear optimisation tasks. Full article

First-phase diets are formulated to help pigs reach a target body weight before switching to a more affordable diet. However, these transitions typically take place on a fixed schedule, which may disadvantage low-body-weight piglets due to their underdeveloped digestive systems and limited feed intake capacity. This study examined the effects of offering low-body-weight (BW) pigs a pre-starter diet until they reached a target BW on growth performance and BW variability. A total of 528 pigs ([Landrace × Yorkshire] × Pietrain), weaned at day 21, representing the smallest 50% of their batch, were divided into medium (5.35 ± 0.31 kg) and small (3.97 ± 0.21 kg) groups based on weaning BW. Pigs received a pre-starter diet either for 10 days (FIXED) or until they reached a target BW of 7.9 kg (TBW), followed by a starter feed. Growth performance between the TBW and fixed strategies was similar over the 36-day period. Overall, mortality was higher in small pigs, though small pigs fed using the fixed strategy showed higher mortality than the rest of the groups between days 10 and 36. This study concludes that offering a pre-starter diet based on target BW, instead of a fixed time, did not significantly improve growth performance or batch uniformity but reduced mortality in small pigs from days 10 to 36. Full article

Two-stage meso- and thermophilic anaerobic digestion (TSMTAD) of food waste was examined and its microbiological structure was investigated. The first stage was designed for the primary storage of perishable food waste and the second stage for central biogas production. Mesophilic storage with initial neutralization and inoculation of lactic acid bacteria (LAB) resulted in an accumulation of lactic acid (21–23 g/L) with a decreased pH, in which bacterial members in facultative hetero-fermentation-type LAB dominated. Repeated fed-batch storage showed stable accumulation of lactic acid, retaining 89.3% (av.) carbon and preventing the growth of exogenous food pathogens. When the second stage of TSMTAD was compared with direct single-stage anaerobic digestion (SSAD) at 55 °C, the amount of methane accumulated was 1.48-fold higher (896 NmL/g-vs.). The methane yield of the original food refuse was 6.9% higher in the case of TSMTAD. The microbial community structures of both cases were similar, consisting of a sole thermophilic hydrogen-assimilating methanogen, Methanothermobacter thermautotrophicus. However, the abundance of bacteria belonging to two functional groups, H₂ CO₂ and acetic acid producer, and syntrophic acetate-oxidizing bacteria increased in TSMTAD. This may change the metabolic pathway, contributing to the stimulation of methane productivity. Full article

Background/Objectives: The rapidly increasing rate of obesity has become an extremely important public health problem, particularly in developed countries. Obesity is associated with a range of health problems, often referred to as the metabolic syndrome. Adipose tissue is now regarded as an endocrine organ responsible for the hormonal secretion of adipokines, which are cytokines involved in various physiological processes. It has been established that adipokines play a key role in the regulation of many processes in the human body. The aim of the current study was to use an animal model to investigate the possible influence of obesity and adipokines on the gestational period, on the development of offspring, and to assess whether these changes are influenced by the administration of antioxidant agents and flavonoids. Methods: The present study was performed using 5 groups of 7 female Wistar albino rats. A control group was used to which a 5% lipid diet was administered, and the other 4 groups were fed an obesogenic 65% lipid diet. From the 4 groups that received obesogenic diet one group received no supplement, and the rest of 3 received Detralex, Sel-E-Vit and Rutin (antioxidants and flavonoids). Study times for both pregnant groups and offsprings: on day 15 of gestation, venous blood was drawn to determine adipokine (leptin and visfatin) levels; on days 18–22 ultrasound examination was performed to measure the thickness of adipose tissue in the abdominal wall; for each batch a number of 10 offspring were selected for the measurements (pup weight, brain weight, head length, head width, spine length, width between shoulder blades, coxal bone length), adipokine levels in the offspring (from brain tissue) were also determined, as well as the existence of changes in the brain tissue of the offspring identified by electron microscopy. Results: The results of the study showed that the high-fat diet (HFD) led to a significant increase in body weight and abdominal wall thickness in pregnant females compared to the control group. The levels of leptin and visfatin were also affected by the HFD, with leptin levels being significantly higher in the HFD group and visfatin levels being lower. In the offspring, the HFD group had a significantly higher body mass and brain weight compared to the control group. The anthropometric measurements of the offspring were also affected by the maternal diet, with the HFD group having larger dimensions overall. Interestingly, the offspring of the groups that received flavonoids in addition to the HFD had significantly smaller dimensions compared to both the HFD group and the control group. Conclusions: The results of this experimental study reinforce what is already known about the effects of obesity on the gestation period and offspring and at the same time, the current study highlights the existence of possible adverse effects of flavonoid compounds on the development of pregnancy and offspring, opening the way for future studies on the benefits and risks of using these compounds during gestational period. Full article

Haematococcus lacustris is a freshwater green microalgae species able to produce and accumulate astaxanthin in response to environmental stresses such as high light and nutrient deprivation. Astaxanthin is a xanthophyll carotenoid of growing economic interest due to its numerous biological activities, notably its strong antioxidant properties, which can be valued in the fields of nutrition, health, feed and aquaculture. The present study aims at evaluating the capacity of two newly isolated Haematococcus strains from the biodiversity of Reunion Island, to be cultivated in a photobioreactor and to produce astaxanthin. The results showed that both strains were able to grow in various nutritive media and to produce and accumulate astaxanthin in response to stresses, mainly in the form of astaxanthin monoesters, which represented up to 2% of the dry biomass weight and which were mostly composed of linoleic and linolenic acids. In fed-batch cultures using 3 L benchtop photobioreactors, the concentrations of biomass enriched in astaxanthin reached up to 3 g L⁻¹ (dry weight) with biomass productivities of 0.04 and 0.02 g L⁻¹ d⁻¹ based on the durations of the vegetative stage and of the entire culture, respectively. In these cultures, the astaxanthin productivities were found to reach on average around 0.25 mg L⁻¹ d⁻¹. Although these results were relatively low compared to the literature, the possibility of improving growth conditions in order to improve biomass and astaxanthin yields, to guarantee economic viability for cultivation at a commercial scale, was further discussed. Full article

The bioconversion of lignocellulosic biomass, which are abundant and renewable resources, into liquid fuels and bulk chemicals is a promising solution to the current challenges of resource scarcity, energy crisis, and carbon emissions. Considering the separation of some end-products, it is necessary to firstly obtain a high concentration separated fermentable sugar solution, and then conduct fermentation. For this purpose, in this study, using acid catalyzed steam explosion pretreated corn stover (ACSE-CS) and corn cob residues (CCR) as cellulosic substrate, respectively, the batch feeding strategies and enzymatic hydrolysis conditions were investigated to achieve the efficient enzymatic hydrolysis at high solid loading. It was shown that the fermentable sugar solutions of 161.2 g/L and 205 g/L were obtained, respectively, by fed-batch enzymatic hydrolysis of ACSE-CS under 30% of final solid loading with 10 FPU/g DM of crude cellulase, and of CCR at 27% of final solid loading with 8 FPU/g DM of crude cellulase, which have the potential to be directly applied to the large-scale fermentation process without the need for concentration, and the conversion of glucan in ACSE-CS and CCR reached 80.9% and 87.6%, respectively, at 72 h of enzymatic hydrolysis. This study also applied the fed-batch simultaneous saccharification and co-fermentation process to effectively convert the two cellulosic substrates into ethanol, and the ethanol concentrations in fermentation broth reached 46.1 g/L and 72.8 g/L for ACSE-CS and CCR, respectively, at 144 h of fermentation. This study provides a valuable reference for the establishment of “sugar platform” based on lignocellulosic biomass and the production of cellulosic ethanol. Full article

This research paper explores biogas production in an underground temperature-controlled fixed dome digester and compares it with a similar uncontrolled digester. Two underground fixed-dome digesters, one fitted with a solar heating system and a stirrer and the other one with an identical stirrer only, were batch-fed with cow dung slurry collected from the University of Fort Hare farm and mixed with water in a ratio of 1:1. The solar heating system consisted of a solar geyser, pex-al-pex tubing, an electric ball valve, a water circulation pump, an Arduino aided temperature control system, and a heat exchanger located at the centre of the digester. Both the digesters were intermittently stirred for 10 min every 4 h. The digester without a heating system was used as a control. Biogas production in the two digesters was compared to assess the effect of solar heating on biogas production. The total solids, volatile solids, and the chemical oxygen demand of the cow dung used as substrate were determined before and after digestion. These were compared together with the cumulative biogas produced and the methane content for the controlled and uncontrolled digesters. It was observed that the temperature control system kept the slurry temperature in the controlled digester within the required range for 82.76% of the retention period, showing an efficiency of 82.76%. Some maximum temperature gradients of 7.0 °C were observed in both the controlled and uncontrolled digesters, showing that the stirrer speed of 30 rpm was not fast enough to create the needed vortex for a uniform mix in the slurry. It was further observed that the heat from the solar geyser and the ground insulation were sufficient to keep the digester temperature within the required temperature range without any additional heat source even at night. Biogas yield was observed to depend on the pH with a strong coefficient of determination of 0.788 and 0.755 for the controlled and uncontrolled digesters, respectively. The cumulative biogas was 26.77 m³ and 18.05 m³ for controlled and uncontrolled digesters, respectively, which was an increase of 33%. The methane content increased by 14% while carbon dioxide decreased by 10% from the uncontrolled to the controlled scenario. The percentage removal of the TS, VS, and COD was 66.26%, 76.81%, and 74.69%, respectively, compared to 47.01%, 60.37%, and 57.86% for the uncontrolled situation. Thus, the percentage removal of TS, VS, and COD increased by 19.25%, 16.44%, and 16.89%, respectively. Full article

In this research work, a main biopolymer group of polyhydroxyalkanoates (PHAs) in the form of polyhydroxybutyrate (PHB) was synthesised by a pure bacterial strain of Azotobacter vinelandii via repeated fed-batch fermentation. An agricultural crop, sugar cane, was used as the sole carbon source. Firstly, batch fermentation was investigated considering variations in incubation times (24 h, 48 h, and 96 h). The highest dry cell weight (DCW) and PHAs of 5.15 ± 0.04 g/L and 4.00 ± 0.04 g/L were obtained after 48 h of incubation time. The optimum time obtained was further varied to investigate the effect of the sugar concentrations in the medium. It was found that bacteria could grow very well and produced the highest DCW and PHAs (11.17 ± 0.15 g/L and 8.77 ± 0.06 g/L) when the culture medium with a 100 g/L sugar concentration was added. Later, repeated fed-batch fermentation was carried out to improve productivity. The results obtained revealed that PHA production was increased in the next cycle of the process. Furthermore, the final productivity (0.104 g/L·h) was increased 1.65-fold compared to the first cycle (0.063 g/L·h). Moreover, the culture strategy showed remarkable results, with reductions in both fermentation time and preparation cost. Full article

Background/Objectives: Tuberculosis continues to be a significant global health concern, causing 1.3 million deaths in 2022, particularly affecting children under 5 years old. The Bacillus Calmette-Guérin (BCG) vaccine, developed in 1921, remains the primary defense against tuberculosis but requires modernized production methods. The recombinant BCG-pertussis strain shows potential in providing dual protection against tuberculosis and whooping cough, especially for vulnerable newborns, and enhanced efficacy against bladder cancer. Implementing submerged cultivation techniques for rBCG-pertussis production can offer increased productivity and standardization. Methods: This study explores a fed-batch cultivation strategy with pH-stat control to feed L-glutamic acid through the acid pump into 1 L bioreactor. Three pH values were evaluated for fed-batch and a simple batch without pH control was done for comparison. The viable cell concentration was compared before and after freeze-drying samples harvested during the cultures. Results: L-glutamic acid was identified as the preferred substrate for rBCG-pertussis. While the fed-batch strategy did not enhance the maximum specific growth rate compared to simple batch cultivation, it did improve the specific growth rate after day 4 in the pH 7.4-controlled fed-batch cultures, thereby reducing the cultivation time. Fed-batch cultures controlled at three pH levels exhibited lower optical density than the simple batch, although the viable cell counts were similar. Notably, samples harvested after day 8 from the simple batch cultures showed a reduction in CFU/mL after freeze-drying, whereas all fed-batch samples exhibited high recovery of viable cell counts post lyophilization. Conclusions: The additional glutamate supplied to the fed-batch cultures may have protected the cells during the lyophilization process. Full article

This study evaluated the potential of Y. lipolytica (CBS 2075 and DSM 8218) to grow in waste motor oil (WMO) and produce valuable compounds, laying the foundation for a sustainable approach to WMO management. Firstly, yeast strains were screened for their growth on WMO (2–10 g·L⁻¹) in microplate cultures. Despite limited growth, the CBS 2075 strain exhibited comparable growth to control conditions (without WMO), while DSM 8218 growth increased 2- and 3-fold at 5 g·L⁻¹ and 10 g·L⁻¹ WMO, respectively. The batch cultures in the bioreactor confirmed the best performance of DSM 8218. A two-stage fed-batch strategy–growth phase in aliphatic hydrocarbons, followed by the addition of WMO (one pulse of 5 g·L⁻¹ or five pulses of 1 g·L⁻¹ WMO), significantly increased biomass production and WMO assimilation by both strains. In experiments with five pulses, CBS 2075 and DSM 8218 strains reached high proteolytic activities (593–628 U·L⁻¹) and accumulated high quantities of intracellular lipids (1.3–1.7 g·L⁻¹). Yeast lipids, mainly composed of oleic and linoleic acids with an unsaturated/saturated fraction > 59%, meet the EU biodiesel standard EN 14214, making them suitable for biodiesel production. Full article

As a high-value bulk chemical, ethylene glycol plays an important role in many fields such as energy, the chemical industry, and automobile manufacturing. At the same time, methanol, as an economical and efficient raw material, has shown great potential in promoting the innovation of bio-based chemicals and fuels. In view of this, this study focused on the excavation and innovative application of enzymes, and successfully designed an efficient artificial cascade catalytic system. The system cleverly converts methanol into ethylene glycol, and the core is composed of methanol dehydrogenase, glycolaldehyde synthase, and lactoaldehyde–pyruvate oxidoreductase. The three enzyme systems work together, which not only simplifies the metabolic pathway, but also realizes the efficient reuse of coenzymes. Subsequently, after ribosome-binding site (RBS) optimization, isopropyl β-D-Thiogalactoside (IPTG) induction regulation, and methanol concentration adjustment, the concentration of ethylene glycol reached 14.73 mM after 48 h of reaction, and the conversion rate was 58.92%. Furthermore, a new breakthrough in ethylene glycol production was achieved within 48 h by using a two-stage biotransformation strategy and fed-batch feeding in a 5 L fermentor, reaching 49.29 mM, which is the highest yield of ethylene glycol reported so far. This achievement not only opens up a new way for the biotransformation of ethylene glycol, but also lays a foundation for the industrial application in this field in the future. Full article

Polyhydroxyalkanoates (PHAs) are polyesters synthesized as a carbon and energy reserve material by a wide number of bacteria. These polymers are characterized by their thermoplastic properties similar to those of plastics derived from the petrochemical industry, such as polyethylene and polypropylene. PHAs are widely used in the medical field and have the potential to be used in other applications due to their biocompatibility and biodegradability. Among PHAs, P(3HB-co-3HV) copolymers are thermo-elastomeric polyesters that are typically soft and flexible with low to no crystallinity, which can expand the range of applications of these bioplastics. Several bacterial species, such as Cupriavidus necator, Azotobacter vinelandii, Halomonas sp. and Bacillus megaterium, have been successfully used for P(3HB-co-3HV) production, both in batch and fed-batch cultures using different low-cost substrates, such as vegetable and fruit waste. Nevertheless, in recent years, several fermentation strategies using other microbial models, such as methanotrophic bacterial strains as well as halophilic bacteria, have been developed in order to improve PHA production in cultivation conditions that are easily implemented on a large scale. This review aims to summarize the recent trends in the production and recovery of PHA copolymers by fermentation, including different cultivation modalities, low-cost raw materials, as well as downstream strategies that have recently been developed with the purpose of producing copolymers, such as P(3HB-co-3HV), with suitable mechanical properties for applications in the biomedical field. Full article

Clavulanic acid is a potent β-lactamase inhibitor produced by Streptomyces clavuligerus, widely used in combination with β-lactam antibiotics to combat antimicrobial resistance. This systematic review analyzes the most successful methodologies for clavulanic acid overproduction, focusing on the highest yields reported in bench-scale and bioreactor-scale fermentations. Studies have demonstrated that glycerol is the preferred carbon source for clavulanic acid production over other sources like starch and dextrins. The optimization of feeding strategies, especially in fed-batch operations, has improved glycerol utilization and extended the clavulanic acid production phase. Organic nitrogen sources, particularly soybean protein isolates and amino acid supplements such as L-arginine, L-threonine, and L-glutamate, have been proven effective at increasing CA yields both in batch and fed-batch cultures, especially when balanced with appropriate carbon sources. Strain engineering approaches, including mutagenesis and targeted genetic modifications, have allowed for the obtainment of overproducer S. clavuligerus strains. Specifically, engineering efforts that overexpress key regulatory genes such as ccaR and claR, or that disrupt competing pathways, redirect the metabolic flux towards CA biosynthesis, leading to high clavulanic acid titers. The fed-batch operation at the bioreactor scale emerges as the most feasible alternative for prolonged clavulanic acid production with both wild-type and mutant strains, allowing for the attainment of high titers during cultivations. Full article

Acetoin biosynthesis by two Bacillus subtilis strains valorising crude glycerol was thoroughly explored within a pre-defined range of culture conditions and systems. B. subtilis ACA-DC 1176 stood out for its higher efficiency in acetoin production, prompting an investigation into the potential for enhanced productivity through the evaluation of diverse culture conditions and media compositions. The primary by-products of the biodiesel and corn industries, namely crude glycerol and corn steep liquor, respectively, were successfully employed as the principal carbon and nitrogen sources of the newly developed low-cost culture medium. Furthermore, the results of the various feeding strategies that were tested indicated that the conversion of 2,3-butanediol (BDO) to acetoin occurred exclusively when the concentration of glycerol was below approximately 5 g/L. This seemed to be necessary for the production of NADH, which is essential for maintaining cellular processes. Following the complete depletion of glycerol, acetic acid increased and became the predominant metabolite, while both acetoin and BDO decreased, presumably resulting in ATP generation. This is likely a mechanism employed by the cell to generate energy in the absence of a carbon source. In the fed-batch bioreactor culture, the kinetics of metabolites differed, as there was no conversion of BDO to acetoin at the final depletion of glycerol. At volumetric mass transfer coefficient (k_La) levels exceeding approximately 70 1/h, the production of acetoin was favoured over that of BDO, with the highest observed acetoin/BDO ratio reaching 4.29 g/g. Conversely, at k_La values below approximately 60 1/h, the titres of acetoin and BDO were found to be nearly equal. The final concentrations of acetoin and BDO reached 36.0 g/L and 25.5 g/L, respectively, resulting in a total yield of both (acetoin + BDO) per glycerol consumption of 0.40 g/g. To the best of our knowledge, this is the first study to focus on acetoin production from crude glycerol fermentative valorisation. The study presents new findings regarding the parameters influencing the level of BDO conversion to acetoin. However, further research is required in order to gain a comprehensive understanding of the underlying phenomena and metabolic pathways involved. Full article