2022年医学专题—5细菌的遗传和变异e.ppt

BacterialGeneticsXiao-KuiGUOPhD第一页，共四十二页。BacterialGenomics第二页，共四十二页。MicrobialGenomics第三页，共四十二页。第四页，共四十二页。第五页，共四十二页。MicrobialGenomeFeatures29%G+Ccontent68%BorreliaburgdorferiDeinococcusradioduranssinglecircularchromosomeGenomeorganizationtwocircularchromosomescircularchromosomepluslargelinearchromosomeplusoneormore21extrachromosomalelementsextrachromosomalelements第六页，共四十二页。PLASMIDSPlasmidsareextrachromosomalgeneticelementscapableofautonomousreplication.AnepisomeisaplasmidthatcanintegrateintothebacterialchromosomeClassificationofPlasmidsTransferpropertiesConjugativeplasmidsNonconjugativeplasmidsPhenotypiceffectsFertilityplasmid(Ffactor)Bacteriocinogenicplasmids.Resistanceplasmids7factors).第七页，共四十二页。Insertionsequences(IS)-Insertionsequencesaretransposablegeneticelementsthatcarrynoknowngenesexceptthosethatarerequiredfortransposition.•a.Nomenclature-InsertionsequencesaregiventhedesignationISfollowedbyanumber.e.g.IS1b.StructureInsertionsequencesaresmallstretchesofDNAthathaveattheirendsrepeatedsequences,whichareinvolvedintransposition.Inbetweentheterminalrepeatedsequencestherearegenesinvolvedin•transpositionandsequencesthatcancontroltheexpressionofthegenesbutnoothernonessentialgenesarepresent.•c.Importancei)Mutation-Theintroductionofaninsertionsequenceintoabacterialgenewillresultintheinactivationofthegene.•ii)Plasmidinsertionintochromosomes-Thesitesatwhichplasmidsinsertintothebacterialchromosomeareatornearinsertionsequenceinthechromosome.•iii)PhaseVariation-Theflagellarantigensareoneofthemainantigenstowhichtheimmuneresponseisdirectedinourattempttofightoffabacterialinfection.InSalmonellatherearetwogeneswhichcodefortwo•antigenicallydifferentflagellarantigens.Theexpressionofthesegenesisregulatedbyaninsertionsequences.Inoneorientationoneofthegenesisactivewhileintheotherorientationtheotherflagellargeneisactive.Thus,Salmonellacanchangetheirflagellainresponsetotheimmunesystems'attack.PhasevariationisnotuniquetoSalmonellaflagellarantigens.Itisalsoseenwithotherbacterialsurfaceantigens.Alsothemechanismofphasevariationmaydifferindifferentspeciesofbacteria(e.g.Neisseria;transformation).第八页，共四十二页。Transposons(Tn)-Transposonsaretransposablegeneticelementsthatcarryoneormoreothergenesinadditiontothosewhichareessentialfortransposition.•Nomenclature-TransposonsaregiventhedesignationTnfollowedbyanumber.•Structure-Thestructureofatransposonissimilartothatofaninsertionsequence.Theextragenesarelocatedbetweentheterminalrepeatedsequences.Insomeinstances(compositetransposons)theterminalrepeatedsequencesareactuallyinsertionsequences.•Importance-Manyantibioticresistancegenesarelocatedontransposons.SincetransposonscanjumpfromoneDNAmoleculetoanother,theseantibioticresistancetransposonsareamajorfactorinthedevelopmentofplasmidswhichcanconfermultipledrugresistanceonabacteriumharboringsuchaplasmid.Thesemultipledrugresistanceplasmidshavebecomeamajormedicalproblem.becausetheindiscriminateuseofantibioticshaveprovidedaselectiveadvantageforbacteriaharboringtheseplasmids第九页，共四十二页。第十页，共四十二页。MechanismofbacterialvariationGenemutation•Genetransferandrecombination•Transformation•Conjugation•Transduction•Lysogenicconversion••Protoplastfusion第十一页，共四十二页。TypesofmutationBasesubstitution•...