细菌的遗传和变异 生物教学课件VIP免费

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。68%DeinococcusradioduransMicrobialGenomeFeaturesG+Ccontent29%BorreliaburgdorferiGenomeorganizationsinglecircularchromosomelargelinearchromosomeplus21extrachromosomalelementscircularchromosomeplusoneormoreextrachromosomalelementstwocircularchromosomes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.IS1•b.StructureInsertionsequencesaresmallstretchesofDNAthathaveattheirendsrepeatedsequences,whichareinvolvedintransposition.Inbetweentheterminalrepeatedsequencestherearegenesinvolvedintranspositionandsequencesthatcancontroltheexpressionofthegenesbutnoothernonessentialgenesarepresent.•c.Importance•i)Mutation-Theintroductionofaninsertionsequenceintoabacterialgenewillresultintheinactivationofthegene.•ii)Plasmidinsertionintochromosomes-Thesitesatwhichplasmidsinsertintothebacterialchromosomeareatornearinsertionsequenceinthechromosome.•iii)PhaseVariation-Theflagellarantigensareoneofthemainantigenstowhichtheimmuneresponseisdirectedinourattempttofightoffabacterialinfection.InSalmonellatherearetwogeneswhichcodefortwoantigenicallydifferentflagellarantigens.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.Thesemultipledrugresistanceplasmidshavebecomeamajormedicalproblembecausetheindiscriminateuseofantibioticshaveprovidedaselectiveadvantageforbacteriaharboringtheseplasmids.第九页，共四十二页。第十页，共四十二页。Mechanismofbacterialvariation•Genemutation•Genetransferandrecombination•Transformation•Conjugation•Transduction•Lysogenicconversion•Protoplastfusion第十一页，共四十二页。Typesofmutation•Basesubstitution...