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Classification of bacteria
- 4. ©Anuswedha Ananthan
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
- 6. ©Anuswedha Ananthan
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
- 7. ©Anuswedha Ananthan
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
- 8. ©Anuswedha Ananthan
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
- 10. ©Anuswedha Ananthan
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)
- 11. ©Anuswedha Ananthan
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)
- 12. ©Anuswedha Ananthan
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
- 13. ©Anuswedha Ananthan
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
- 14. ©Anuswedha Ananthan
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
- 15. ©Anuswedha Ananthan
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
- 16. ©Anuswedha Ananthan
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
- 17. ©Anuswedha Ananthan
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.