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1、Bacterial GeneticsXiao-Kui GUO PhDBacterial GenomicsMicrobial Genomics68%Deinococcus radioduransMicrobial Genome FeaturesG+C content29%Borrelia burgdorferiGenome organizationsingle circular chromosomelarge linear chromosome plus21 extrachromosomal elementscircular chromosome plus one or moreextrachr
2、omosomal elementstwo circular chromosomesPLASMIDS PLASMIDS PlasmidsPlasmidsareareextrachromosomalextrachromosomalgeneticelementsgeneticelementscapableofautonomousreplication.Ancapableofautonomousreplication.An episomeepisomeisaisaplasmidplasmidthatcanthatcanintegrateintothebacterialchromosomeintegra
3、teintothebacterialchromosomeClassification ofClassification of Plasmids Plasmids TransferpropertiesTransferproperties ConjugativeConjugative plasmids plasmids Nonconjugative plasmidsNonconjugative plasmids PhenotypiceffectsPhenotypiceffects FertilityFertility plasmid plasmid (F factor) (F factor) Ba
4、cteriocinogenic plasmidsBacteriocinogenic plasmids. . ResistanceResistance plasmids plasmids 7 factors) 7 factors) . .Insertionsequences(IS)-InsertionsequencesareInsertionsequencesaretransposablegeneticelementsthatcarrynoknowngenesexceptthosethataretransposablegeneticelementsthatcarrynoknowngenesexc
5、eptthosethatarerequiredfortransposition.requiredfortransposition. a.a.NomenclatureNomenclature-InsertionsequencesaregiventhedesignationISfollowedbya-InsertionsequencesaregiventhedesignationISfollowedbyanumber.e.g.IS1number.e.g.IS1 b.b.StructureStructure InsertionsequencesaresmallstretchesofDNAthatha
6、veattheirendsInsertionsequencesaresmallstretchesofDNAthathaveattheirendsrepeatedsequences,whichareinvolvedintransposition.Inbetweentheterminalrepeatedsequences,whichareinvolvedintransposition.Inbetweentheterminalrepeatedsequencestherearegenesinvolvedintranspositionandsequencesthatcanrepeatedsequence
7、stherearegenesinvolvedintranspositionandsequencesthatcancontroltheexpressionofthegenesbutnoothernonessentialgenesarepresent.controltheexpressionofthegenesbutnoothernonessentialgenesarepresent. c.c.ImportanceImportance i)Mutation-Theintroductionofaninsertionsequenceintoabacterialgenewillresultini)Mut
8、ation-Theintroductionofaninsertionsequenceintoabacterialgenewillresultintheinactivationofthegene.theinactivationofthegene. ii)ii)PlasmidPlasmidinsertionintochromosomes-Thesitesatwhichinsertionintochromosomes-Thesitesatwhichplasmidsplasmidsinsertintotheinsertintothebacterialchromosomeareatornearinser
9、tionsequenceinthechromosome.bacterialchromosomeareatornearinsertionsequenceinthechromosome. iii)PhaseVariation-Theiii)PhaseVariation-Theflagellarflagellarantigensareoneofthemainantigenstowhichtheantigensareoneofthemainantigenstowhichtheimmuneresponseisdirectedinourattempttofightoffabacterialinfectio
10、n.Inimmuneresponseisdirectedinourattempttofightoffabacterialinfection.InSalmonellatherearetwogeneswhichcodefortwoSalmonellatherearetwogeneswhichcodefortwoantigenicallyantigenicallydifferentdifferentflagellarflagellar antigens.Theexpressionofthesegenesisregulatedbyaninsertionsequences.Inoneantigens.T
11、heexpressionofthesegenesisregulatedbyaninsertionsequences.Inoneorientationoneofthegenesisactivewhileintheotherorientationtheotherorientationoneofthegenesisactivewhileintheotherorientationtheotherflagellarflagellar geneisactive.Thus,Salmonellacanchangetheirflagellainresponsetotheimmunegeneisactive.Th
12、us,Salmonellacanchangetheirflagellainresponsetotheimmunesystemsattack.PhasevariationisnotuniquetoSalmonellasystemsattack.PhasevariationisnotuniquetoSalmonellaflagellarflagellarantigens.Itisalsoantigens.Itisalsoseenwithotherbacterialsurfaceantigens.Alsothemechanismofphasevariationmayseenwithotherbact
13、erialsurfaceantigens.Alsothemechanismofphasevariationmaydifferindifferentspeciesofbacteria(e.g.differindifferentspeciesofbacteria(e.g.NeisseriaNeisseria;transformation).;transformation).Transposons(Tn)-TransposonsTransposons are transposable are transposable genetic elements that carry one or more o
14、ther genes in addition to genetic elements that carry one or more other genes in addition to those which are essential for transposition.those which are essential for transposition. NomenclatureNomenclature - - Transposons Transposons are given the designation are given the designation Tn Tn followe
15、d by a followed by a number.number. StructureStructure - The structure of a - The structure of a transposon transposon is similar to that of an insertion is similar to that of an insertion sequence. The extra genes are located between the terminal repeated sequence. The extra genes are located betwe
16、en the terminal repeated sequences. In some instances (compositesequences. In some instances (composite transposons transposons) the terminal repeated ) the terminal repeated sequences are actually insertion sequences. sequences are actually insertion sequences. ImportanceImportance - Many antibioti
17、c resistance genes are located on - Many antibiotic resistance genes are located on transposons transposons. . SinceSince transposons transposons can jump from one DNA molecule to another, these can jump from one DNA molecule to another, these antibiotic resistanceantibiotic resistance transposons t
18、ransposons are a major factor in the development of are a major factor in the development of plasmidsplasmids which can confer multiple drug resistance on a bacterium which can confer multiple drug resistance on a bacterium harboring such aharboring such a plasmid plasmid. These multiple drug resist
19、ance. These multiple drug resistance plasmids plasmids have have become a major medical problem because the indiscriminate use of become a major medical problem because the indiscriminate use of antibiotics have provided a selective advantage for bacteria harboring theseantibiotics have provided a s
20、elective advantage for bacteria harboring these plasmidsplasmids.MechanismofbacterialvariationGene mutationGene transfer and recombination TransformationTransformationConjugationConjugationTransductionTransductionLysogenicLysogenicconversionconversionProtoplastfusionProtoplastfusionTypes of mutation
21、Base substitutionFrame shefitInsertion sequencesWhat can cause mutation?Chemicals: nitrous acid; alkylating agents5-bromouracilbenzpyreneRadiation: X-rays and Ultraviolet lightVirusesBacterial mutationMutation rateMutation and selectivityBackward mutationTransformationTransformation is gene transfer
22、 resulting from the uptake by a recipient cell of naked DNA from a donor cell. Certain bacteria (e.g. Bacillus, Haemophilus, Neisseria, Pneumococcus) can take up DNA from the environment and the DNA that is taken up can be incorporated into the recipients chromosome. Conjugation Transfer of DNA from
23、 a donor to a recipient by direct physical contact between the cells. In bacteria there are two mating types a donor (male) and a recipient (female) and the direction of transfer of genetic material is one way; DNA is transferred from a donor to a recipient.Physiological States of F FactorAutonomous
24、 (F+)Characteristics of FCharacteristics of F+ + x F x F- - crosses crossesF F- - becomes F becomes F+ + while F while F+ + remains F remains F+ +Low transfer of donor Low transfer of donor chromosomal geneschromosomal genesF+Physiological States of F FactorIntegrated (Hfr)Characteristics of Charact
25、eristics of HfrHfr x F x F- - crosses crossesF F- - rarely becomes rarely becomes HfrHfr while while HfrHfr remains remains HfrHfrHigh transfer of High transfer of certain donor certain donor chromosomal chromosomal genesgenesF+HfrPhysiological States of F FactorAutonomous with Autonomous with donor
26、 genes (F)donor genes (F) Characteristics of F Characteristics of F x Fx F- - crosses crossesF F- - becomes F becomes F while F remains while F remains F FHigh transfer of High transfer of donor genes on donor genes on F and low F and low transfer of other transfer of other donor donor chromosomal c
27、hromosomal genesgenesHfrFMechanism of F+ x F- CrossesDNA transferOrigin of Origin of transfertransferRolling circle Rolling circle replicationreplication Pair formation Conjugation bridgeF+F-F+F-F+F+F+F+Mechanism of Hfr x F- CrossesDNA transferDNA transfer Origin of transferOrigin of transfer Rollin
28、g circle Rolling circle replicationreplicationHomologous Homologous recombinationrecombination Pair formation Conjugation bridgeHfrF-HfrF-HfrF-HfrF-Mechanism of F x F- CrossesDNA transferDNA transfer Origin of Origin of transfertransfer Rolling circle Rolling circle replicationreplication Pair forma
29、tion Conjugation bridgeFFFFFF-FF-RPlasmidTransduction: Transductionisdefinedasthetransferofgeneticinformationbetweencellsthroughthemediationofavirus(phage)particle.Ittherefore does not require cell to cellcontactandisDNaseresistant.Generalized Transduction Generalized transduction is transduction in
30、 which potentially any bacterial gene from the donor can be transferred to the recipient.The mechanism of generalizedtransductionGeneralized transduction1.It is relatively easy. It is relatively easy. 2.It is rather efficient (10It is rather efficient (10-3-3 per recipient with per recipient with P2
31、2HT, 10P22HT, 10-6-6 with P22 or P1), using the with P22 or P1), using the correct phage. correct phage. 3.It moves only a small part of the It moves only a small part of the chromosome which allows you to change chromosome which allows you to change part of a strains genotype without affecting part
32、 of a strains genotype without affecting the rest of the chromosome. the rest of the chromosome. 4.The high frequency of transfer and the The high frequency of transfer and the small region transferred allows fine-small region transferred allows fine-structure mappingstructure mappingSpecialized tra
33、nsductionSpecialized transductionSpecialized transduction is transduction in is transduction in which only which only certain donorcertain donor genesgenes can be can be transferred to the recipient. transferred to the recipient. Different phages may transfer different genes Different phages may tra
34、nsfer different genes but anbut an individual phage can only transfer certain individual phage can only transfer certain genesgenesSpecialized transduction is mediated by Specialized transduction is mediated by lysogeniclysogenic or temperate phage and the genes or temperate phage and the genes that
35、 get transferred will depend on where the that get transferred will depend on where the prophageprophage has has inserted in the chromosome.inserted in the chromosome.The mechanism of specialized transductionSpecialized transduction 1.Very efficient transfer of a small region-can be Very efficient t
36、ransfer of a small region-can be useful for fine-structure mapping useful for fine-structure mapping 2.Excellent source of DNA for the chromosomal Excellent source of DNA for the chromosomal region carried by the phage, since every phage region carried by the phage, since every phage carries the sam
37、e DNA. carries the same DNA. 3.Can often be used to select for deletions of Can often be used to select for deletions of some of the chromosomal genes carried on the some of the chromosomal genes carried on the phage. phage. 4.MerodiploidsMerodiploids generated using specialized generated using spec
38、ialized phage can be quite useful in complementation phage can be quite useful in complementation analyses.analyses.Lysogenicconversion The prophage DNA as a gene recombined with chromosome of host cell.ProtoplastFusion Fusion of two protoplasts treated withlysozymeandpenicillin.ApplicationofBacterialVariationUseinmedicalclinic:Diagnosis,Treatment,Prophylaxis.UseinGeneticEngineering
