The document discusses the classification of bacteria according to Bergey's Manual. It provides: - An overview of the history and purpose of Bergey's Manual in classifying and identifying bacteria since 1923. - Details on the 9th edition's classification of bacteria into two domains (Archaea and Bacteria) based on rRNA sequencing. - Summaries of the major phyla, classes, orders and genera of bacteria, including both Gram-positive and Gram-negative groups. - Descriptions of important pathogenic and non-pathogenic bacteria referenced in Bergey's Manual.

1. Classification of Bacteria
Any discussion dealing with bacterial classification can not do any through acquaintance with a
book named Bergesys Manualwhich has remained an authentic source of exhaustive information about all
known bacteria for more than 80 years.
BergeysMnnual:
In 1923,David Hendricks Bergey, professor of bacteriology at the university of Pennsylvania and four
colleagues published a classification of bacteria that could be used for identification of bacterial species,
“Bergeys Manual of Determinative bacteriology”.
Bergeys Manual: Classifying and Identifying prokaryotes
Bergeys manual of Determinative
Bacteriology
Provides identification schemes for
identifying bacteria and archaea.
Morphology, differential staining,
biochemical tests.
Standard reference for laboratory
identification of bacteria.
Bergeys Manual of Systematic
Bacteriology
Provides phylogenic information on
bacteria and archaea.
Based on rRNA sequencing.
Standard reference on bacterial
classification.
 The manual is now in its 9th edition.
 The first 8 edition of this book were published under the tittle “Bergeys Manual of Determinative
Bacteriology”
How it is arranged?
DIVISION EXAMPLE
Edition First, Second
Volume 1,2,3,4,5.
First edition has 4 volumes
Second edition have 5 volumes
Parts A, B,C,etc
Vol.2 have three parts (2A,2B and 2C)
Vol.5 have two parts (5A,5B)
Vol.1,3,4 have no parts
Chapter Volume 2, part A contain 24 chapter
First edition:
Volume 1(1984)- Gram negative bacteria orgeneral, medical or industrial importance.
Volume 2(1986)-Gram positive other than Actinomycetes
Volume3(1989)- Archaebacteria ,Cyanobacteria and remaining Gram negative bacteria.
Volume 4(1991)- Actinomycetes.

2. Second edition:
Volume 1(2001)- The archaea , The deeply branching and phototropic bacteria
Volume 2 (2005)– The proteobacteria
Volume 3(2009)- The low GC gram positive bacteria
Volume 4(2011)- The high GC gram positive bacteria
Volume 5(2012) – The planctomycetes, spirochaetes, fiberobacteres, Fusobacter, Bacterioidetes.
Selected Prokaryotes from Bergeys Manual of Systematic Bacteriology,Second
Edition:
Phylum
class
Order Important
genera
Special feature
Chlamydae Chlamydiales Chlamydia
Chlamydophila
Intracellular parasites,human
pathogens Intracellular
parasites,human pathogens
Spirochaetes Spirochaetale Borrelia
Leptospira
Trepanoma
Human patghogens
Human pathogens
Human pathogens
Bacteriodales Bacteroidales Bacteroids
Prevotella
Human intestinal tract
Human oral cavity
Fusobacteria Fusobacteriales Fusabacterium Human intestinal tract
DOMAIN
ARCHEA
Crenarchaeota
Euryarchaeota
Desulfurococcales
Sulfolobales
Methanobacteriales
Halobacteriales
Pyrodictium
Sulfolobus
Methanobacterium
Halobacterium
Halococcus
Hyperthermophiles
Hyperthermophiles
Methanogens
Require high salt conc.
Require high salt conc.
 Till the 7th edition published in 1957, bacteria together with virus were placed in a division called
Protophyta under the plant kingdom.
 In the 8thedition ,published in 1974 , the bacteria were brought under a separate kingdom ,
Prokaryotes and virus were exclude.
The second edition of Bergeys manual of Systematic Bacteriology (2001) recognizes 2 domains in which all
prokaryotes’ organisms are included i.e.
1.Archaea
2. Bacteria

3. 1. Domain Archaea:-
 The domain archaea have been divided into 2 phyla-i. Crenarchaeota
ii. Euryarchaeota
 The Crenarchaeota includes the extreme thermophiles, acidophiles and sulphur metabolizing
archaebacteria.
 The euryarchaeota includes extreme thermophiles anaerobic methanogens and extreme halophiles.
 The 2 phyla have been divided mainly on the basis of differences in the 16s rRNA sequences.
General characteristics of Archaebacteria: -
1. Archaebacteria may be Gram +ve or Gram -ve.
2. Cells with a cell wall except those of Thermoplasma, a wall less Mycoplasma like genus.
3. Though organisms may be aerobic, anaerobic,
chemo lithotrophic or chemoorganotrophic.
4. They mostly occur in extreme environments
though some are mesophilic.
5. An outer membrane characteristically present in
the Gram -ve true bacteria is absent in
archaebacteria.
6. Murein is absent in the cell wall of both Gram +ve
and Gram -ve archaebacteria.
7. In some methanobacterium a peptidoglycan like polymer called Pseudomurein is present.
A. Phylum Crenarchaeota:-
The phylum is a comparative small one.
It consists of a single class i.e, Thermoprotei.
The single class divided into 3 orders- i-Thermoproteus
ii-Desulfurococcous

4. iii-Sulfolobus
B. Phylum Euryarchaeota:-
The phylum euryarchaeota is much larger and more diverse than crenarchaeota.
There are some 46 genera which can be grouped into 4 major types-
i- Methanogen- Are strictly anaerobic, requiring a low redox potential for optimal
growth. E.g- Methanococcous.
Ii-Extreme Halophiles- Ability to grow at very high salt concentration.
E.g.- Halobacterium.
iii- Thermoplasma- Lack a cell wall, growing at high temperature.
E.g-Thermococcous.
iv- Thermophilic cocci
Domain Archaea
2. Domain Bacteria:-
 All prokaryotic organisms except Archaebacteria have been included in the domain bacteria of the
2nd edition of Bergey’s Manual of systematic bacteriology’
 Bacteria all commonly known as eubacteria have been classified phylogenetically mainly on the
basis of 16s r RNA homology in this edition.
 Though emphasis on r RNA is a new trend and is in contrast to the 1stedition, where mainly the
phenotypic characters formed on the basis of classification.
Gram +ve Bacteria: -
A. High GC Group: -
 All these morphological types are placed in a single phylum Actinobacteria having only one class
called actinobacteria.
 There are many genera, some of which include important pathogen, while many others are of
economic importance.
1. Streptomyces – largest genus actinomycetes.
- Occurs extensively in soil where they play an important role in the process of
mineralization.
- They are best known as producer of antibiotic.
2.Nacardia- mycolic acid is present in their cell wall.
- they are weakly acid fast.
Crenarchaeota Euryarchaeota
orders orders
Thermoproteus Desulfurococcous Sulfolobous Methnogens Halophiles Thermoplasma Thermophilic
cocci

5. 3.Mycobacterium -include two very important human pathogen- i. M. tuberoculosis (human)
ii. M. leprae (leprosy)
- M. bovis (tubercular disease of cattle)
- M. avis (tubercular infection in birds)
- M. lepraemurium (leprosy of rat)
4.Corynebacterium – it includes mostlyharmless saprophytic soil bacteria ,except one C. diphtheriae .
- C. diphtheriae produces an exotoxin.
5. Frankia- organisms which infect some 178 species of non leguminous trees and shrubs to produces
actively nitrogen fixing root nodules .
-Frankia species infect host cells either through root hair, like rhizobia or by intracellular
penetration.
6. Bravibacterium- some members have strong proteolytic activity e.g., B. linens takes part in maturation
of chees.
7. Propionibacterium- They produces propionic acid from a variety of sugars like glucose, lactose, and
pentose and also from organic acid like lactate malate etc. They contribute substantially to the production
swisschees.P. Acne has been associated with acne formation in skin.
8. Bifidobacterium- they occur usually as commensal organism in the oral cavity, urogenital tract and the
intestine. B. bifidum is present as an intestinal organism typically in breast fed babies. They are generally
non pathogenic.
B. Low GC group:-
 In the 2nd edition of the manual, the low G+C Gram +ve bacteria have been placed in the phylum
Firmicutes.
 Phylum Firmicutes has 3 classes –i. Mollicutes
ii. Clostridia
iii. Bacilli
 On the basis of r RNA homology, they have included into the low G+C group of Gram+ve bacteria
though mycoplasma don not respond to Gram +ve stain.
 A notable deviation from earlier edition of the manual is that the actinomycetes have been
separated from Firmicutes on the basis of their high G+C content of DNA.
 Besides mollicutes, the low low GC group included 2 main types, the aerobic bacilli and the
anaerobic clostridia.
1. Mollicutes :-
 The most important character of the mollicutes is that their cells are not surrounded by a cell wall
– a character shared also by some archaebacteria like theromoplasma.
 These bacteria are unable to synthesise the precursor of peptidoglycans, the main components of
bacterial wall.
 Due to absence of cell wall , mollicutes are highliy plastic and pleomorphic
 They are considered as the smallest free living bacteria .
 The cells are surrounded by a triple layered doubled membrane containing sterols.
 The class mollicutes having some main genera, which are mycoplasma, spiroplasma ,
achaeloplasma , anaeroplasma etc.

6. 2. Clostridia :-
 In the second edition of the manual, the class clostridium has been divided into three orders – i.
clostridiales, ii. Thermoanaerobacterials iii. Haloanaerobiales.
 Among three clostridiales is the largest order.
3. Bacilli:-
Class – Bacilli
Orders
Bacillales Lactobacillales
(9 family) (6 family)
Important Genera important genera
a. Bacillus a. lactobacillus
b.Caryophalon b. pediocuccus
c. Thermoactinomyces
d.Sporolactobacillus
e.staphylococcus
Gram –ve Bacteria:-
 On the basis of r RNA homology , the Gram -ve bacteria are for more diverse than the Gram +ve
ones.
 The anoxygenic photosynthesizer -chlorobi and oxygenic photosynthesizer – cyanobacteria are
primitive and Gram -ve bacteria.
 The largest phylum of Gram negative bacteria is Proteobacteria.
 The proteobacteria has been divide into 5 classes - alpha, beta, gamma, delta and ephpsilon.
 Outside this complex phylum and primitive bacteria, several others have been created to
accommodate the rest Gram negative bacteria.
 Morphologically these bacteria not only have the usual coccal, rod shaped, spiral and curved cells,
all having a rigid walk, but also stalked filamentous, flexible cells.
 Some bacteria form specilized spores e.g.-Myxospores.
 Besides normal chemooganotrophy, there are forms showing chemolithotrophy,
photoorganotrophy and photolithotrophy.
 In addition Diazotrophy and Methylotrophy are also known.
 All grades of oxygen relationship occur in these bacteria, starting from fully aerobic to obligate
anaerobic.
 These bacteria are classified into 5 phylum-
i Chlamydia.
ii.spirochaetes
iii.Bacterodetes
iv.Plantomycetes
v.Proteobacteria
 Among of these five phylum Proteobacteria is the largest phylum.

7. PHYLUM PROTEOBACTERIA:-
 Proteobacteria is the largest phylum of the gram negative bacteria.
 It constitute the largest group among all eubacteria comprising five classes –
a. Class- alpha proteobacteria
b.Class - beta proteobacteria
C.Class- gamma proteobacteria
D.Class- delta proteobacteria
E.Class-epsilon proteobacteria
a. Alpha Proteobacteria:-
 On the basis of 16s rRNA homology,the alpha proteobacteria are phylogenetically related to each
other.
 Nevertheless, the bacteria are morphologically as well as physiologically highly diverse.
PHYSIOLOGICAL GROUP REPRESENTATIVE GENERA
 Phototrophic  Rhodospirillum,Rhodopseudomonas
 Chemolithotrphic  Nitrobacter,Nitrococcus
 Methylotrophic  Methylobactrerium
 Symbiotic diazotrophic  Rhizobium,Bradyrhizobium,Mesorhizobium
 Non symbiotic diazotrophic  Beijernckia,Derxia,Azospirillum
 Pathogenic  Rickettsia,Agarobacterium,Brucella
B.Beta Proteobacteria:-
 The class proteobacteria has also been divided into six orders containing bacteria which are
morphologically and physiologically diverse.
 There are –
1. Cocci Niesseria
2. Simple Rod Thiobassilus
3. Ellipsoidal cells Nitrozomonas
4. Cocco-bacilli Bordetella
5. Spirilli Spirullum
6. Rod shaped covered with sheath Spherotilus
C. Gamma proteobacteria:-
 Gamma proteobacteria is largest class in phylum proteobacterium.
 Many organisms of this class are physiologically and pathologically important .
 The largest and the important order of gamma proteobacteria is enterobacteriales, which consists
of a single family enterobacteriaaceae having 41 genera.

8. Enterobacteria :-
 They so named because they are present in the large intestine of man and other animal.
 Majority of them carry out mixed acid fermentation producing a variety of organic acid like acetic
acid, lactic acid, formic acid, succinic acid etc.
 Some members can ferment lactose to Produce acid and gas and they are commonly known as
coliform bacteria e.g. E.colli.
D. Delta Proteobacteria:-
 More than half of these bacteria include the anaerobic sulphate reducing bacteria.
 The rest includes Myxobacteria which form characterstics microfruiting bodies and the genus
Bdellovibrio,which parasitizes other bacteria.
 The bacteria possess the ability to transfer electron from the cytochrome to sulphate acting as a
terminal electron acceptor in place of oxygen which is absent under anaerobic condition.this
process is known is known as Disimilarity sulphate reduction.
 The small order Bdellovibrionales includes the intresting genus Bdellovibrio,which is parasite on
other gram negative bacteria.
 The order Myxococcales of Delta proteobacteria encompasses myxobacteria which are
characterised by formation of fruiting bodies.
E.Epsilon Proteobacteria:-
 It is the smallest class of proteobacteria comprising of a single order called Campylobacteriales.
 There are two well known genera i.e. Campylobacter and Helicobacter
 Campylobacter-(Microaerophilic)
C.jejuni- Diarrhoeal disease in man
C.fetus- known to cause abortion in cattle
 Helicobacter pylori-(Microaerophilic)
-Found in the human gastric mucosa and having implicated as a cause of Duodenal and Gastric
ulcer.
-They produce abundant urease .
- The ammonia released by the enzymatic action might damage the mucous membrane of
stomach.
Special groups of gram negative bacteria:-

9. 1.Anoxygenic photosynthetic bacteria :-
 Anoxygenic photosynthetic bacteria are defined by their ability to grow using enrgy from light
without evolving oxygen .
 The dominate groups are
Purple-sulfur bacteria ---------------------Thiospirillium,Chromatium
Purple-non sulfur bacteria-----------------Rhodospirillium,Rhodopseudomonas,
Heliobacterium(G+ve)
Green sulfur bacteria ----------------------Chlorobium
Green non sulfur bacteria -----------------Chloroflexus
 They have bacteriophyll and carotenoid and photochemical reaction centres which generates ATP
and cellular reductants used for corbondioxide fixation.
 The pigment bearing structures in bacteria are called chromatophores .
 These structures contain the entire component of photosynthetic pigment and the enzyme of
photosynthetic electrontransport.
2. Oxygenic Photosynthetic bacteria:-
 Cyanobacteria carryout a plant like photosynthesis using water as exogenous electron for
photosynthetic reduction of NADP producing oxygen as a by product
 Cyanobacteria differs from other photosynthetic bacteria in possessing chlorophyll alike green
plant, but they don’t have chlorophyll b.
 Cell mass generally has a blue green colour and may also appear red.
Blue colour is due to-phycocyanin
Green colour due to-green chlorophyll pigment
Red colour due to-phycoerythrin
 The organisms reproduce by means of binary fission,budding ,fragmentation of trichomes into
hormogonia, which are short chain of 5-15 cells
 Many filamentous cyano bacteria form also thick walled resting pores known as akinetes
 Another very characteristics structure formed in some filamentous cyanobacteria is a heterocyst
(produced by the differentiation of a vegetative cell of the trichome).within heterocyst the
nitrogenous enzyme is synthesized
 On the surface of thylakoid numerous hemispherical bodies are orderly arranged these are known
as phycobilisomes
 It is believed as cyanobacteria were among the earliest colonisers of this planet
3.Methylotrophic Bacteria:-
 most of them are obligately methane oxidisers,able to oxidise one carbon compound like methyl
alcohol,methyl nitrogen,formal dehyde formic acid but are unable to utilise methane.
 Both methane oxidiser as wel as those oxidising one carbon compounds named as methylotrophs.
E.g. alpha proteobacteria-methylophilla,methylobacterio
beta proteobacteria-methylophilus,methylobacillus
gamma proteobacteria-methylo coccus ,methylo bacter.

10. 4.Nitrifying Bacteria:-
Nitrification is the conversation of ammonia (NH3) to nitrite (NO2
-
), and then nitrate (NO3
-
). This
process is carried out by bacteria in the soil, with different species carrying out different reactions.
Ammonia and nitrates are reactive compounds which are able to be used by plants in a process
known as assimilation.
Nitrifying bacteria are chemolithotrophic organisms that include species of genera such as
Nitrosomonas, Nitrosococcus, Nitrobacter, Nitrospina, Nitrospira and Nitrococcus. These bacteria
get their energy from the oxidation of inorganic nitrogen compounds.

11. CONCLUSION:-
“Bergeys’ Manual of suystematic bacteriology” is a schizomycetes classification
systemused by old bacteriologists and has a global reputation.its based on the international
committee of bacteriological nomenclatures international rules of bacteria and virus nomenclature
,established in 1947.it was a mono mental work representing collaborating efforts of over hundred
of worlds best microbiologists when it was assembled. Acc to Bergeys’ manual ,the total no. Of
bacteria species is around 1500.these are classified into 10 orders based on morphological
characterstics and flagella type.