微生物学第4讲 Bacterial Heredity and Variation

BacterialHeredityandVariation:BacterialGeneticsLecture4

2023/3/28TakeanasalswabfromthewholeclassandStreptococcuspneumoniaeisisolatedfrom20people.Arethese20S.pneumoniaeisolatesthesame?WhatifwesamplefromthewholeJTU/community/Shanghai?Willtheisolatesbethesame?Whatifwecomparethesecarrierisolateswiththeisolatescollectedfrompatients?Whatifwecomparetheisolateswitharchievestrainscollected100or1000yearsago?2023/3/282023/3/28GeneticdiversityandevolutionTakeanasalswabfromthewholeclassandstreptococcuspneumoniaeisisolatedfrom40people.Arethese40S.pneumoniaeisolatesthesame?WhatifwesamplefromthewholeJTU/community/Shanghai?Willtheisolatesbethesame?Whatifwecomparethesecarrierisolateswiththeisolatescollectedfrompatients?Whatifwecomparetheisolateswitharchievestrainscollected100or1000yearsago?2023/3/28BacterialGeneticsisthestudyofbacterialheredityandvariationHeredity(inheritance):The“likeness”ofthecharacteristicsofprogenyandparent.Variation:Thedifferencebetweenprogenyandparent.Phenotypicvariation:canbetemporaryandreversibleGenotypicvariation:permanentandinheritable2023/3/28Phenomenaofvariationshapeandstructurevariation:LformVirulencevariation:BCGvaccinestrain.Resistancevariation:antibioticsColonyvariation:Smoothrough

30g/LNaCl

Yersiniapestispolymorphism

oldculturemedium

2023/3/28BacterialGenome

——ThegeneticmaterialChromosome:onebigpiececircularDNAMobilegeneticelementProphage

ExtrachromosomalgeneticelementsPlasmids2023/3/28Chromosome

Onelong,singlemoleculeofdoublestranded,circularorlinearDNAContainingfrom580kbtomorethan4600kbofDNA

NCBIgenomedatabase2023/3/282023/3/28GenomeorganizationSpeciesDNAmoleculesSize(Mb)NumberofgenesEscherichiacoliK-12Onecircularmolecule4.6394397VibriocholeraeElTorN16961TwocircularmoleculesChromosome12.9612770Chromosome21.0731115DeinococcusradioduransR1FourcircularmoleculesChromosome12.6492633Chromosome20.412369Megaplasmid0.177145Plasmid0.04640BorreliaburgdorferiB31sevenoreightcircularmolecules,11linearmoleculesLinearchromosome0.911853Circularplasmidcp90.00912Circularplasmidcp260.02629Circularplasmidcp32*0.032NotknownLinearplasmidlp170.01725Linearplasmidlp250.02432Linearplasmidlp28-10.02732Linearplasmidlp28-20.03034Linearplasmidlp28-30.02941Linearplasmidlp28-40.02743Linearplasmidlp360.03754Linearplasmidlp380.03952Linearplasmidlp540.05476Linearplasmidlp560.056NotknownThereare5or6similarversionsofplasmidcp32perbacterium.2023/3/28MobileGeneticElementsTheyaremobilegeneticelementsthatcanmovefromonepositiontoanotherinthegenomeorbetweendifferentmoleculesofDNA.

Insertionsequences

(IS)

:Thesimplesttransposons;carrynoknowngenesexceptthosethatarerequiredfortransposition(＜2kb)Transposons(Tn):transposablegeneticelementsthatcarryoneormoreothergenesinadditiontothosethatareessentialfortransposition.(＞2kb)MutatorphageIS

ISResistanceGene(s)Tn2023/3/28Somepathogenicbacteriauseasimilarmechanismtocoordinatetheexpressionofasystemofvirulencefactors.Thegenesfortheactivitymaybegroupedtogetherinapathogenicityorvirulenceisland,whichissurroundedbytransposon-likemobileelementsallowingthemtomovewithinthechromosomeandtootherbacteria.

(EHEC,EPEC)locusforenterocyteeffacement(LEE)2023/3/28PlasmidsExtrachromosomalgeneticelements;circular,double-strandedDNAmoleculesAutonomously

replicate,independentlyofthebacterialchromosomeCarrygeneticinformation,whichmaynotbeessentialbutcanprovideaselectiveadvantagetothebacteriaTransferable

plasmidschromosomalDNA2023/3/282023/3/28BacteriocinsToxinsMetabolizingsomesubstratesFertilityplasmidResistanceplasmidFunctionof

plasmid2023/3/28BacteriophageBacteriophages(phages)areobligateintracellularparasitesthatmultiplyinsidebacteriabymakinguseofsomeorallofthehostbiosyntheticmachinery.Theyarevirusesthatinfectbacteria.2023/3/28StructureofBacteriophage

Differentsizesandshapes

icosahedralfilamentous2023/3/28TailTailFibersBasePlateHeadContractileSheathCapsidDNA2023/3/28TypesofBacteriophageLyticorVirulentPhages

LysogenicorTemperatePhage

2023/3/28LyticorVirulentPhagesDefinition:

Lyticorvirulentphagesarephageswhichcanonlymultiplyinbacteriaandkillthecellbylysisattheendofthelifecycle.LifeCycleAdsorptionPenetration

BiologicalSynthesisMaturationandRelease

2023/3/282023/3/282023/3/28LysogenicorTemperatePhageLysogenicortemperatephages

arethosethatcaneithermultiplyviathelyticcycleorenteraquiescentstateinthecell.Inthisquiescentstatemostofthephagegenesarenottranscribed;thephagegenomeexistsinarepressedstate.ThephageDNAinthisrepressedstateiscalledaprophagebecauseitisnotaphagebutithasthepotentialtoproducephage.InmostcasesthephageDNAactuallyintegratesintothehostchromosomeandisreplicatedalongwiththehostchromosomeandpassedontothedaughtercells.Thecellharboringaprophageistermedalysogenicbacterium.2023/3/28Prophage2023/3/28Lysogenicbacterium2023/3/28LysogeniccycleandlyticcycleMitomycinC2023/3/28Whenacellbecomeslysogenized,occasionallyextragenescarriedbythephagegetexpressedinthecell.Thesegenescanchangethepropertiesofthebacterialcell.Thisprocessiscalledlysogenic

conversion.LysogenicconversionC.diphtheriaephageC.diphtheriaetoxin(-)C.diphtheriaetoxin(+)2023/3/28MechanismofbacterialvariationGenemutationGenetransferandrecombination

TransformationTranspositionConjugationTransduction2023/3/28GeneMutationMutationisanerrorduringDNAreplicationthatresultsinachangeinthesequenceofdeoxyribonucleotidebasesintheDNA.2023/3/281.PointMutationCause-duetoaddition,deletionorsubstitutionofoneormorebases.Types-Transition:apurinebase(A:G)isreplacedbyapurinebaseorapyrimidinebase(T:C)isreplacedbyanotherpyrimidinebase.Mostcommontype.Transversion:substitutionofapurinebasebyapyrimidinebase&viceversa2023/3/281.PointMutationResultsofmutation-

Missensemutation–tripletcodeisalteredsothatadifferentaminoacidispresentataparticularpositionintheprotein.Nonsensemutation–convertsacodonthatspecifiesanaminoacidintoaterminationcodon.

2023/3/282.FrameShiftMutationCause-Deletionorinsertionofabase-changesallofthecodonsdownstreamfromthechange2023/3/283.LethalMutation

Mutationinvolvesvitalfunctionsandresultsinthedeathoftheorganism–nonviablemutation.Aconditionallethalmutantmaybeabletoliveundercertainconditions–permissiveconditions.Commonesttypeofconditionalmutantisthetemperaturesensitive(ts)mutantwhichisabletoliveatthepermissivetemperatureof30Cbutnotattherestrictivetemp(39C).

2023/3/284.SuppressorMutation

ReversalofamutantphenotypebyanothermutationatapositionontheDNA,distinctfromthatoftheoriginalmutation.

2023/3/28HorizontalGenetransferandrecombination

Bacterialgeneticexchangeistypifiedbytransferofarelativelysmallfragmentofadonorgenometoarecipientcell.ThetransferreddonorDNAmaythenbeintegratedintotherecipient'snucleoid(recombination)byvariousmechanisms.SuccessfulgeneticrecombinationdemandsthatthisdonorDNAbereplicatedintherecombinantorganism.2023/3/28NaturalmechanismsofgenetransferandrecombinationinbacteriaincludeTransformationConjugationTransductionTransposition2023/3/28Downloadedfrom:StudentConsult(on4September201309:04PM)©2005Elsevier2023/3/28TransformationTheprocessbywhichbacteriatakeupfragmentsofnakedDNAandincorporatethemintotheirgenomes.

2023/3/28Transformation(FrederickGriffith,1928)

2023/3/28Downloadedfrom:StudentConsult(on4September201309:04PM)©2005ElsevierLibraryconstructionandgenecloning2023/3/28Conjugation

FirstdescribedbyLederburg&Tatumin1946inastrainofE.colicalledK12.AdonorormalebacteriumpassesDNAdirectlytoarecipientorfemalebacteriumbyaconjugationtube(sexpili).Thefemalebacteriumattainsdonorstatus&inturncanconjugatewithotherfemalecells.Malenessisdeterminedbythepresenceofaplasmidwhichcodesforsexpili.Theplasmidiscalledthesexfactororfertilityfactor(Ffactor)R(resistance)factorcanalsobetransferredbyconjugation2023/3/28F-PilusforConjugationF-pilus:encodedbytheplasmidof“fertilityfactor(Ffactor)”2023/3/28F+conjugationF+F-F+F-F+F+F+F+DonorRecipientF+oriT2023/3/28HfrConjugationWhenitexistsasafreeplasmid,theFplasmidcanonlytransferitself.Thisisn’tallthatusefulforgenetics.However,sometimestheFplasmidcanbecomeincorporatedintothebacterialchromosome,byacrossoverbetweentheFplasmidandthechromosome.Theresultingbacterialcelliscalledan“Hfr”,whichstandsfor“Highfrequencyofrecombination”.HfrbacteriaconjugatejustlikeF+do,buttheydragacopyoftheentirechromosomeintotheF-cell.2023/3/28Hfr(highfrequencyrecombinant)conjugationAnF+plasmidinsertsintothedonorbacterium'snucleoidtoformanHfrmale.2023/3/28ThesexpilusadherestoanF-female(recipient).OnedonorDNAstrandbreaksatoriToftheinsertedF+plasmid.2023/3/28Thesexpilusretractsandabridgeformsbetweenthetwobacteria.OnedonorDNAstrandbeginstoentertherecipientbacterium.Thetwocellsbreakaparteasilysotheonlyaportionofthedonor'sDNAstrandisusuallytransferredtotherecipientbacterium.2023/3/28ThedonorbacteriummakesacomplementarycopyoftheremainingDNAstrandandremainsanHfrmale.TherecipientbacteriummakesacomplementarystrandofthetransferreddonorDNA.2023/3/28ThedonorDNAfragmentundergoesgeneticexchangewiththerecipientbacte