Classification of bacteria

©Anuswedha Ananthan
Anuswedha Ananthan
Assistant Professor
Department of Microbiology
Justice Basheer Ahmed Sayeed College for Women
Chennai

TAXONOMY
CLASSIFICATION
NOMENCLATURE
IDENTIFICATION

CLASSIFICATION- PRINCIPLES
 CHARACTERISTICS USED IN
CLASSIFICATION
 1. CLASSICAL/PHENOTYPIC
 Morphological,chemical
composition,cultural,physiological &
metabolic,antigenic,pathogenicity,ecological
characteristics.
2. MOLECULAR/GENOTYPIC
comparison of proteins, NA base
composition,NA hybridisation,NA sequencing

CLASSIFICATION SYSTEMS
INTUITIVE METHOD
NATURAL CLASSIFICATION
PHENETIC CLASSIFICATION
PHYLETIC/PHYLOGENETIC
CLASSIFICATION

NUMERICAL TAXONOMY
 Five steps involved in numerical taxonomy
 1. Selection of strains
 2. Selection of tests
 3. Coding and arranging of test results in
 a format suitable for analysis by computer
 4. Computer analysis
 5. Preservation and interpretation of results

 a =number of characters positive in both strains
 b =number of characters positive in
 strain 1 and negative in strain 2
 c =number of characters negative in
 strain 1 and positive in strain 2
 d =number of characters negative in both strains
 Similarity coefficient (Sj) = a/a + b + c
 Matching coefficient (Ss) = a + d/a + b + c + d
 Sj = does not take into account characters negative
for
 both organisms (only positive matches)
 Ss = includes both positive and negative matches

 Advantages of numerical taxonomy
 1. Objective
 2. Stable
 3. Compares a large number of characters
 after thorough investigation
 4. Is easy to revise and refine upon further research
 5. Computer does the work
 Disadvantages of numerical taxonomy
 1. Does not rely upon evolutionary distribution of
strains
 2. Is based on methods that may vary from
 lab to lab or year to year
 3. Gives equal weight to certain characters that
 may represent differences in genetic complexity
 4. Similarity between groups does not mean
 relatedness at the genotypic level

Classification of bacteria
 Levels of Classification/taxonomic structuring
 A group or “level” of classification
 Hierarchical; broad divisions are divided up into smaller
divisions:
 Kingdom (Not used by most bacteriologists)
 Phylum (Called “Division” by botanists)
 Class
 Order
 Family
 Genus (plural: Genera)
 Species (Both singular & plural)

Definition of “Species
 The “basic unit” of taxonomy, representing a specific,
recognized type of organism
 For sexually reproducing organisms, a fundamental
definition of “species” has been reproductive compatibility
 This definition fails for many microbial species (including
bacteria), because they do not reproduce sexually
 Classic definition: A collection of microbial strains that share
many properties and differ significantly from other groups of
strains
 Species are identified by comparison with known “type
strains”: well-characterized pure cultures; references for the
identification of unknowns
 There are several collections of type strains, including the
American Type Culture Collection (ATCC)

 Strain:
 A population of microbes descended from a
single individual or pure culture
 Different strains represent genetic variability
within a species
 Biovars: Strains that differ in biochemical or
physiological differences
 Morphovars: Strains that vary in morphology
 Serovars: Stains that vary in their antigenic
properties

 Bergey’s Manual
 DavidBergey in 1923.
 2 books-
 1.Bergey’s Manual of DeterminativeBacteriology-
culturedbacteria-9th ed
 2. 1.Bergey’s Manual of Systematic Bacteriology-all known
bacteria-2nd edition

Bergey’s manual of Systematic Bacteriology
 1st edition:
 Classification based on phenetic system
 Prokaryotes divided into 4 volumes
 1. G-ve bacteria of general, medical or industrial
importance
 2. G+ve bacteria other than actinomycetes
 3. G-ve bacteria with distinctive
properties,cyanobacteria & archaea
 4.Actinomycetes

 2nd edition:Classification based on phylogenetic
relationships;5 vol
VOLUME ORGANISMS DESCRIBED
1. The Archaea & deeply branching &
phototrophic bacteria
Includes archaea, cyanobacteria, green
sulfur & non-sulfur bacteria, deinococci
7 other branching forms
2. The Proteobacteria All proteobacteria
3.The Low G+C gram +ve bacteria G+C% below 50-55%-Clostridia,
bacilli,Streptococci,staphylococci,mycopl
asma
4. The High G+C gram +ve bacteria G+C% above 50-
55%,corynebacteria,Mycobacteria,Nocard
ia,Actinomycetes
5. The Planctomycetes, Spirochaetes,
Fibrobacteres,Bacterioides &
Fusobacteria
Different G-ve bacteria,
Chlamydias,spirochaetes

BERGEY’S MANUAL OF DETERMINATIVE BACTERIOLOGY
 4 Major categories
 1. G-ve eubacteria that have cell walls
 2. G+ve eubacteria that have cell walls
 3. Eubacteria lacking cell walls
 4. The Archaebacteria.
 35 different groups

NOMENCLATURE
 BINOMIAL NOMENCLATURE
 1.Genus/Generic name
 2. Species name/Specific epithet
 Common/coloquial name
 Purpose: 1. for international communication
 2. to prevent any confusion by
using vernacular names.

INDENTIFICATION
Few characteristics listed to identify
only that isolate and no other.
Characteristics chosen must be easy to
determine
IDENTIFICATION methods
1. identification keys
2. identification tables

Classification of bacteria

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