Bacterial Taxonomy: Classification of Bacteria & Nomenclature

Bacterial Taxonomy: Classification of
bacteria
&
Nomenclature
By: Hafiza Asfa Shafique

Microbiology
BS Biotechnology V
Bacterial Taxonomy
• Bacterial Taxonomy: is the science dealing with
description, identification, naming and classification
of bacteria.
• This is a Greek word
– taxis = arrangement or order
– nomos = law or science
• Three sub disciplines
– Classification
– Nomenclature
– Identification
Importance
• Helps in classifying and arranging components of
diversity of bacteria
• Helps bacteriologists to make predictions and frame
hypotheses for further research based on knowledge
of identical bacteria
• bacterial taxonomy contributes particularly in the
area of clinical microbiology
The phylogenetic Tree of life based on small
subunit rRNA sequencing
The phylogenetic Tree of life based on small
subunit rRNA sequencing
Levels of Bacterial Taxonomy
Nomenclature
• The rules are set in International code for the
nomenclature of Bacteria.
• Bacteria are named according to binomial system
developed by Carl Von Linnaeus
• Names that cause error or confusion should be rejected
• A species is designated with Latin or Latinized names i.e.,
genus and species
– The first word (genus) is always capitalized
– The second word (species or specific epithet) is not capitalized
– Both genus and species name, together referred to as species, are
either underlined or italicized when appearing in print
Nomenclature
• Taxonomic names approved by the International
committee of systematic Bacteriology are considered
official and binding.
• The correct name of a species or higher taxonomic
designations is determined by valid publication
• Examples
– Salmonella typhi
– Escherichia coli
Classification of Bacteria
Basis of Bacterial Classification
• Classical characteristics
– Phenotypic characters
(morphological, nutrition, staining, cultural characteristics,
environmental factors, biochemical reactions, physiological
and metabolic, ecological etc.)
• Molecular characteristics
– genomic DNA
– GC content ratios
– DNA DNA hybridization
– nucleic acid sequencing
Classification of bacteria on the basis of
mode of nutrition
1. Phototrophs
2. Chemotrophs
3. Autotrophs
4. Heterotrophs
1. How the organism obtains carbon for synthesizing cell mass:
• Autotrpohic: carbon is obtained from carbon dioxide (CO2)
• Heterotrophic: carbon is obtained from organic compounds
• Mixotrophic: carbon is obtained from both organic compounds and
by fixing carbon dioxide
2. How the organism obtains reducing equivalents (hydrogen atoms or
electrons) used either in energy conservation or in biosynthetic
reactions:
• Lithotrophic: reducing equivalents are obtained from inorganic
compounds
• Organotrophic: reducing equivalents are obtained from organic
compounds
3. How the organism obtains energy for living and
growing:
• Phototrophic: energy is obtained from light
• Chemotrophic: energy is obtained from
external chemical compounds
1. Autotrophs
• Those bacteria which uses carbon dioxide (CO2) as sole
source of carbon to prepare its own food.
• Prepare food and gain energy by processes; photosynthesis
(in the presence of light) or chemosynthesis (gain energy
using chemical compounds)
• Autorophs further divided into:
1. Photoautotrophs:
2. Chemoautotrophs
2. Phototrophs:
• Those bacteria which gain energy from light
1. Photo-organotrophs:
• obtain energy from light
• carbon and reducing equivalents for biosynthetic reactions from organic
compounds, such as succinate.
2. Photo-lithotrophs:
• obtain energy from light and carbon from the fixation of carbon dioxide
• using reducing equivalents (hydrogen and electron source) from
inorganic compounds, such as H2S as electron source.
• Examples: Cyanobacteria (H2O as reducing equivalent as hydrogen
donor), Chromatiaceae (hydrogen sulfide (H2S) as hydrogen
donor), Chloroflexus (H2 as reducing equivalent donor)
3. Chemotrophs
• Energy is obtained from external chemical compounds
• They utilize chemical compounds for assimilation of CO2
• They cannot carry out photosynthesis
1. Chemo-organotrophs:
• obtain energy, carbon, and hydrogen for biosynthetic reactions from organic
compounds, such as glucose and amino acids.
• Examples: most bacteria, e. g. Escherichia coli, Bacillus spp., Actinobacteri,
Pseudomonas pseudoflava
2. Chemo-lithotrophs
• obtain energy from the oxidation of inorganic compounds and carbon
from the fixation of carbon dioxide, such as NH3 as electron source.
• Examples: Nitrifying bacteria, sulfur-oxidizing bacteria, iron-oxidizing
bacteria,
4. Heterotrophs
• Those bacteria which uses organic compound as
carbon source
• They lack the ability to fix CO2
• Most human pathogenic bacteria
• Some heterotrophs are simple
• Some bacteria that require special nutrients for their
growth; known as fastidious heterotrophs.
Bacterial Classification based
on Environmental Factors
Classification of bacteria on the basis
of optimum temperature of growth
1. Psychrophiles
2. Mesophiles
3. Thermophiles
4. Hyperthermophiles
1. Psychrophiles:
• They grow at 0°C or below but
• the optimum temperature is 15 °C or below
• maximum temperature is 20°C
• have polyunsaturated fatty acids in their cell membrane
which gives fluid nature to the cell membrane even at
lower temperature.
• Examples: Vibrio psychroerythrus, vibrio marinus,
Psychroflexus
2. Mesophiles:
• grow best between (25℃ -40℃) but
• optimum temperature for growth is 37 ℃
• Most of the human pathogens are mesophilic
in nature
• Examples: E. coli, Salmonella, Klebsiella,
Staphylococci
3. Thermophiles:
• These bacteria best grow above 45 ℃.
• Thermophiles contains saturated fatty acids in
their cell membrane, so their cell membrane
does not become too fluid even at higher
temperature.
• Examples: Streptococcus thermophiles,
Thermus aquaticus
4. Hyperthermophiles:
• optimum temperature of growth above 80℃.
• Mostly Archeobacteria.
• Monolayer cell membrane of Archeobacteria is
more resistant to heat and
• they adopt to grow in higher temperature.
• Examples: Pyrolobus fumari, Thermotoga
Classification of bacteria on the basis of optimum pH of growth
1. Acidophiles
2. Alkaliphiles
3. Neutrophiles
1. Acidophiles:
• Those bacteria that grow best at acidic
pH
• The cytoplasm of these bacteria are
acidic in nature.
• Some acidophiles are thermophilic in
nature, such bacteria are called
Thermoacidophiles.
• Examples: Thermoplasma, Sulfolobus
2. Alkaliphiles:
• Those bacteria that grow best at alkaline pH
• optimum pH of growth is 8.2
• Example: vibrio cholerae:
3. Neutrophiles:
• Those bacteria that grow best at neutral pH
(6.5-7.5)
• Example: E. coli
Classification of bacteria on the
basis of Morphology
• It is divided into six classes.
– Coccus
– Bacilli
– Mycoplasma
– Spirochaetes
– Rickettsiae and Chlamydiae
– Actinomycetes
Rickettsiae and Chlamydiae
• They are obligate intracellular parasites

resemble more closely to viruses than
bacteria
• 2 groups of Gram-negative bacteria
• They are fully dependent on host.
Classification of bacteria on the
bases of gaseous and soil
requirement
Soil requirement
1. Halophiles
• They required high concentration of NaCl
• Their cell membrane is made up of
o Glycoprotein
o Glutamic acid
o Aspartic acid
• Examples:
o Archeobacteria
o Halobacterium
o Halococcus
2. Halotolerant:
• Does not require NaCl
• Can tolerate low concentration of NaCl
• Tolerate 2% of salt
• Examples
o Penicillium
o Cladosporium
o Aspergillus
Bacterial classification on the basis of
Gaseous requirement
• 1. Obligate aerobes:
• bacteria require oxygen
• cannot grow in the
absence of O2.
• These bacteria carryout
only oxidative type of
metabolism.
• Examples; Mycobacterium,
Bacillus
2. Facultative anaerobes
• do not require O2 but can
use it if available.
• Growth of bacteria become
batter in presence of O2
• These bacteria carryout
both oxidative and
fermentative type of
metabolism
• Examples: coli, Klebsiella,
Salmonella
3. Aerotolerant anaerobes;
• Those bacteria do not require O2 for growth but can
tolerate the presence of O2.
• Insensitive to the oxygen presence, their growth is
not affected by the presence of O2.
• These have only fermentative type of metabolism.
• Example: Lactobacillus and Streptococci, both found
in the oral microbiota.
4. Microaerophiles:
• Microaerophilic bacteria require a reduced oxygen concentration

for growth.
• They have optimal growth in 5-10% oxygen
• some species are stimulted by 1-10% carbon dioxide
(capnophiles).
• They are not killed outright by the presence of oxygen per se, but
are able to tolerate only sub-atmospheric levels of oxygen in their
environment.
• At atmospheric level of Oxygen growth of these bacteria is
inhibited.
• Microaerophilic bacteria are examples of aerotolerant anaerobes
• Example: Campylobacter jejuni, which causes gastrointestinal
infections
5. Obligate anaerobes:
• Those bacteria that can grow only in absence of
Oxygen.
• Oxygen is harmful to obligate anaerobes
• These bacteria have only fermentative type of
metabolism
• Examples: Peptococcus, Peptostreptococcus,
Slostridium, methanococcus
6. Capnophiles:
• Those bacteria grow best at high concentration carbon

dioxide (CO2) and a lower concentration of oxygen than
present in the atmosphere .
• They are CO2 loving organism
• Most of the microaerophiles are capnophilic in nature.
• Example: Campylobacter, Helicobacter pylori, Brucella abortus
Classification of bacteria on the basis of Spore formation
Spore forming bacteria:

• Those bacteria that produce spore
during unfavorable condition.
• These are further divided into two
group
i) Endospore forming bacteria:
• Spore produced within the bacterial
cell.
• Bacillus, Clostridium,
Sporosarcina etc
ii) Exospore forming bacteria:
• Spore produced outside the cell
• Methylosinus
iii) Non sporing bacteria:
• those bacteria which do not produce
spore.
• Eg. E. coli, Salmonella

Bacterial Taxonomy: Classification of Bacteria & Nomenclature

Uploaded by

Copyright:

Available Formats

Bacterial Taxonomy: Classification of Bacteria & Nomenclature

Uploaded by

Document Information

Original Description:

Original Title

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

Bacterial Taxonomy: Classification of Bacteria & Nomenclature

Uploaded by

Copyright:

Available Formats

Bacterial Taxonomy: Classification of

By: Hafiza Asfa Shafique

• They are obligate intracellular parasites

• Microaerophilic bacteria require a reduced oxygen concentration

• Those bacteria grow best at high concentration carbon

Spore forming bacteria:

You might also like