Bacterial Taxonomy 03

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Introduction Taxonomy : science of classification Provides orderly basis for identification of organisms and placing them into various categories Need for taxonomy: 1) to establish criteria for identification 2) to arrange related organisms into groups 3) to provide information how they evolved


History Carolus Linnaeus : father of Taxonomy Originated Binomial nomenclature Ernst. H. Haeckel - Kingdom Protista Lynn Margulis & H.F. Copeland - Kingdom Monera R.H. Whittaker – 5 Kingdom Classification He separated Fungi but retained bacteria in kingdom Monera

Concepts of Taxonomy:

Concepts of Taxonomy 3 basic concepts: 1) Classification 2) Nomenclature 3) Identification


Classification Def.: systematic division of organisms into related groups based on similar characteristics Organization of microbes that share similar morphologic, physiologic, and genetic traits into specific groups or taxa Speciation of a microbe is done at the time the organism is classified and named. Classification of individual microbes may vary from time to time.


Taxa Arranged in hierarchy Kingdom Division Class Order Family Genus Species

Species :

Species Most basic taxonomic group. It is a collection of strains that share many common and genetic features and differ notably from other groups Strain: defined as the descendants of a pure culture In turn divided into Sub species Subspecies divided into Biotypes, Serotypes or Genotypes Share specific characters but differ in minor characters.

Genus :

Genus Comprises of different species having important common features But differ sufficiently to maintain their status as individual species Grouping into genus – based on various phenotypic & genetic charecters shared by the species Higher taxa designations not generally used for bacteria

Phylogentic Classification:

Phylogentic Classification Type of hierarchal classification representing branching tree appearance with one characteristic employed at each level Denotes evolutionary arrangement of species Divisions, Classes, Orders, Families, Genera & Species. Important characteristics like Lactose fermenting properties to differentiate major groups Minor characteristics like production of enzymes to differentiate minor groups

Adansonian Classification:

Adansonian Classification Introduced by Michael Adanson in 18 th century Avoids weighted characteristics Considers all the characters expressed at time of study Called Phenetic system Computer analysis allows identification of large no. of characteristics Classification based on large no. of characters known as numerical taxonomy

Numerical Taxonomy:

Numerical Taxonomy Based on idea that by increasing the no. of characters observed, the accuracy in identification can be increased. It is very much developed by advent of computers Helps to establish evolutionary relationships The more no. of characters organisms share, the more closely they are related. If 2 organisms share 90% or more of characters, they are of same species.

Genetic Classification:

Genetic Classification Based on genetic homology Studied by extracting DNA and studying the base pair sequence by hybridization or recombination methods Study of mRNA and rRNA gives genetic relatedness 16S ribosomal RNA studies show evolutionary relationships among organisms

Nomenclature :

Nomenclature Naming of organisms based on established rules and guidelines By International Code for Nomenclature of Bacteria. Binomial nomenclature Genus and species name derived from Latin or Greek derivation


Contd. Genus designation always capitalized Species designation not capitalized Names should be italicized or underlined in print In case of changes, the previous name to be followed with in parentheses E.g. Stenotrophomonas (Pseudomonas) maltophila

Identification :

Identification Process of characterizing a given microorganism to determine its classification, its relatedness to the other similar or dissimilar organisms & by these processes assign a name to the organism By various biochemical tests & genetic assays

Practical steps :

Practical steps 1) Have a pure culture 2) Determine whether you have chemolithotrophic autotroph , or photosynthetic organism or chemoheterotrophic organism 3) Examine cells by Grams stain & other stains if necessary 4) Examine growth characteristics & other unique features


Contd. 5) Test for oxygen requirement 6) Test for dissimilation of glucose – Oxidative or Fermentative 7) Complete additional tests selected by scanning the characteristics for cluster of genera to which the organism is assigned based on initial tests

Taxonomic Keys:

Taxonomic Keys Dichotomous taxonomic keys For identifying groups of bacteria Each key – 2 paired statements “either- or” Can be used for staining reaction, metabolic reactions, growth at different temperatures, cultural characteristics and properties of colonies on solid media

Three Domain Classification:

Three Domain Classification Proposed by Woese in 1990 States that from a common ancestor Bacteria and Archaea first seperated and then Eukarya seperated from Archaea Domains rank above Kingdom Also postulates that a 4 th domain that directly gave genes to Eukarya which became extinct Proven by Universal genetic code

Intraspecies Classification:

Intraspecies Classification Sub classify species based on 1) biochemical properties (Biotypes), 2) antigenic properties (Serotypes), 3) susceptibility to phage (Phagetypes), 4) production of bacteriocins(Colicintypes), 5) presence of specific genes (Genotypes)

Intraspecies Classification:

Intraspecies Classification 1) Biotyping : relies on set of biochemical reactions. E.g. biochemical reactions 2) Serotyping : based on difference in antigenic expression on the cell 3) Bacteriocin typing : by susceptibility to bacteriocins 4) Phagetyping : for bacteria to which lytic bacteriophages were identified; epidemiological significance

Genotypic Classification:

Genotypic Classification Depends on differences related to genome of bacteria Techniques employed: Plasmid profile analysis RFLP analysis 16S RNA sequencing Restriction endonuclease analysis

Reference Collections of Microbes:

Reference Collections of Microbes Necessary to provide a stability & continuity of organisms For taxonomic & epidemiologic purposes To compare the isolated mutants Study of genetic loci & nutrition & biochemical pathways First by Prof. Frantisek Kral of Prague in 1900’s

Contd. :

Contd. Individual microbiologosts maintained in early part of century 1947 International Federation of Type Culture Collections formed Later on many reference collections emerged ATCC, NCTC, MTCC etc.

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