Bacterial Classification and Nomenclature

1 Bacterial Classification and NomenclatureFaculty: Dr. RakeshSharda Taxonomyisthescienceoftheclassificationo forganisms,withthegoalofshowingevolution aryrelationshipsamongorganisms. Taxonomyincludes:(a)Identification.(b)No menclature.(c) is TaxonomyIdentification istheprocessofstudyingandrecordingtheide nticalanddistinguishingfeaturesNomenclat ure istheorderlyarrangementoforganismsintogr oups,preferablyinaformat, of Taxonomy , of bacteria Livingorganismswereoncedividedintoonlytw okingdoms:plantaeandanimaliae:bacteria,f ungi,andalgaewereclassifiedwithplants;pr otozoawereclassifiedasanimals. Haeckelin1865proposedthirdkingdomProtist aforunicellularmicroorganismssuchasbacte ria,algae,fungiandprotozoa. BacteriawereseparatedintotheKingdomProca ryotaeorMonerain1969byWhittaker fivekingdomsWhittaker 5 Kingdom classificationBasedoncellularorganizatio nandnutritionalpatterns:ProcaryotaeorMon era-prokaryotic,unicellular,variablenutr itionpatterns ,unicellularorcolonial,heterotrophic protozoa,slimemolds, ,unicellularormulticellular,heterotrophi corabsorptive molds,yeasts, ,multicellularorcolonial,autotrophic plants,somealgae,mosses, ,multicellular,heterotrophicoringestive Three Domains(Carl Woese and George Fox, 1977)Currently,livingorganismsaredivided intothreesuperkingdoms,calledasdomains, Eukarya Domaininclude plants, animals, fungi, and protists Eubacteria Domain include bacteria with peptidoglycan in cell wall.

2 Archaea Domain include bacteria(Archaea) with unusual cell walls BasedoncellularrRNAssequenceprimarily cellmembranelipidstructureandsensitivity toantibiotics. rRNAmoleculesthroughoutnaturecarryoutthe samefunctionandgeneticallystableverylitt leovertime. Thissystemproposesthatacommonancestorcel l("Cenancestor")gaverisetothreedifferent celltypes, Cellular DomainsThe Archaea(archaebacteria) Archaeaareprokaryoticcells. containrRNAthatisuniquetotheArchaeadisti nctlydifferentfromtherRNAofBacteriaandEu karya. cellmembranescomposedofbranchedhydrocarb onchainsattachedtoglycerolbyetherlinkage s. cellwallsofArchaeadoesnothavepeptidoglyc an. Archaeaarenotsensitivetosomeantibioticst hataffecttheBacteria, Bacteria(eubacteria) Bacteriaareprokaryoticcells. containrRNAthatisuniquetotheBacteriadist inctlydifferentfromtherRNAofArchaeaandEu karya. celllmembranescomposedofunbranchedfattya cidchainsattachedtoglycerolbyesterlinkag es.

3 Cellwallscontainpeptidoglycan. Eukarya(eukaryotes) Eukaryahaveeukaryoticcells. containrRNAthatisuniquetotheEukaryadisti nctlydifferentfromtherRNAofArchaeaandBac teria. Cellmembranescomposedofunbranchedfattyac idchainsattachedtoglycerolbyesterlinkage s. NotallEukaryapossesscellwall,butthosehav ingacellwalldoesnotcontainspeptidoglycan . Morphological characteristics Biochemical tests Serological tests Phage typing Sequences of amino acids in proteins Percentage of G-C pairs in the nucleic acid Number and sizes of DNA fragments produced by restriction enzymes Sequence of bases in 16S rRNA(Ribotyping)NomencaltureofBacteriaSc ientificNomenclature Accordingtoscientificnomenclature,eachba cteriaisassignedtwonames(binomialnomencl ature):agenusandaspecies. :EubacteriaKingdom:ProcaryotaeDivision/P hylum:GracilicutesClass:ScotobacteriaFam ily:EnterobacteriaceaeGenus:EscherichiaS pecies:coliMethods of Classifying BacteriaThe Intuitive KeyNumerical taxonomyInthismethodoftaxonomyofmany(100 to200)characteristicsforeachbacterialstr ainisdetermined, (%S)ofeachstraintoeveryotherknownstraini scalculatedbytheformula:%S = ND/NS +NDwhere,NS=numberofcharacteristicsthata resame(positiveornegative)forthetwostrai ns,ND= TaxonomyGenetic Relatedness mostreliablemethodofclassification basedonthedegreeofgeneticrelatednessbetw eenorganisms reliesuponG+Ccontent,DNAhomology,ribosom alRNAhomology(16 SrRNAforprokaryotesand18 SrRNAforeukaryotes ribotyping).

4 Genetic HomologyGenetic homologies (similarities) can be determined by looking at: Base compositions DNA-DNA or DNA-RNA Hybridization DNA or RNA sequencingBergey s ManualThe Bergey s Manual Bergey s Manual of Determinative bacteriology Internationalstandardforbacterialtaxonom y. Firstpublishedin1923. 9editionshavebeenpublished. From1980itisrenamedasBergey sManualofSystemicBacteriologypublishedas a4volumesetfrom1984. In2012 5volumeset. CurrentlyBergey'sManualofSystematicsofAr chaeaandBacteria(2015),anonlinebook, sManualofSystematicBacteriology,bacteria wereclassifiedin33sectionsbasedonphenoty pic, : Procaryotae Divisions: Gracilicutes(thinskin):ProcaryoteswithaG ram-negativecellwall. Firmicutes(thickskin):ProcaryoteswithaGr am-positivecellwall. Tenericutes(softortenderskin):Procaryote sthatlackacellwall. Mendosicutes(skinwithfaults) ,butsolelyon16 Sphylogeny