医学微生物学课件：2 细菌的遗传与变异

1、Bacterial GeneticsSection 1 bacterial VariationsMorphology and structureL form, H-O, capsuleVirulenceBCG, lysogenic diphtheria ResistanceColonyS-RAntigenicityS-RSection 2 genetic materialsChromosomePathogenicity island : C+GPlasmidConjugative , nonconjugative Bacteriophage (phage,噬菌体)Viruses that ar

2、e associated with prokaryotes, or simply, bacterial viruses.Transposable element (转位因子)The results of phage infectionsVirulent phagelytic bacteriaTemperate phage (lysogenic phage)lysogenic bacteria, prophage temperate phage and bacterial lysogenyprophage(前噬菌体)lysogenic bacterium(溶原性细菌)lysogenic conv

3、ersion(溶原性转换)diphtheria toxinbotulinThe phage DNA can integrate into the recipient cell DNA, and the cell can acquire a new trait, this process is called lysogenic conversion.lysogenic conversion (溶原性转换)Assay for Lytic PhagePlaque assayMethodPlaque forming unit (pfu)Measures infectious particles Bac

4、teriaPhage+PhageTransposable element(转位因子)Also named Jumping genes(跳跃基因) or movable genes(移动基因)Insertion sequence, IS (插入序列)Less than 2kbpTransposon, Tn(转座子)More than 2kbpFunctional genesTypes of Transposable Genetic ElementsInsertion sequences (IS)Definition: Elements that carry no other genes exce

5、pt those involved in transpositionNomenclature - IS1Structure Importance MutationPlasmid insertionTransposaseABCDEFGGFEDCBATypes of Transposable Genetic ElementsTransposons (Tn) Definition: Elements that carry other genes except those involved in transpositionNomenclature - Tn10StructureComposite Tn

6、s Importance Antibiotic resistanceIS ISResistance Gene(s)IS ISResistance Gene(s)(complex Tn)复合型转座子Section 3 Genetic Mechanism of Bacterial VariationMutationSpontaneous mutationInduced mutationGene transfer and recombinationDonor chromosome, plasmidphagerecombinationTransformation(转化)The direct uptak

7、e of donor DNA by the recipient cellConjugation(接合)Plasmid (sex pili)-mediated genetic recombination in bacteriaTransduction(转导)phage-mediated genetic recombination in bacteriaLysogenic conversion(溶原性转换)prophage Protoplast fusion(原生质融合)TransformationDefinition: Gene transfer resulting from the uptak

8、e of DNA from a donor.Factors affecting transformationDNA size and stateSensitive to nucleasesCompetence(感受态) of the recipient Competence factorsInduced competenceTransformationStepsUptake of exogenous DNARecombinationSignificance Recombinant DNA technology转化 (transformation)Transformation is the tr

9、ansfer of DNA itself from one cell to another. In nature, dying bacteria may release their DNA, which may be taken by the recipient cells.ConjugationDefinition: Gene transfer from a donor to a recipient by direct physical contact between cellsMating types in bacteriaDonorF factor (Fertility factor)F

10、 (sex) pilusRecipientLacks an F factorMechanism of F+ x F- Crosses Pair formationConjugation bridgeDNA transferOrigin of transferRolling circle replicationPhysiological States of F FactorAutonomous (F+)Characteristics of F+ x F- crossesF- becomes F+ while F+ remains F+Low transfer of donor chromosom

11、al genesPhysiological States of F FactorIntegrated (Hfr，高频重组菌株)Characteristics of Hfr x F- crossesF- rarely becomes Hfr while Hfr remains HfrHigh transfer of certain donor chromosomal genesF+Hfr高频重组菌Mechanism of Hfr x F- CrossesDNA transferOrigin of transferRolling circle replicationHomologous recom

12、bination Pair formation Conjugation bridgePhysiological States of F FactorAutonomous with donor genes (F)Characteristics of F x F- crossesF- becomes F while F remains FHigh transfer of donor genes on F and low transfer of other donor chromosomal genesConjugationSignificanceGram- bacteriaAntibiotic r

13、esistanceRapid spreadGram+ bacteriaProduction of adhesive material by donor cells conjugation (接合)Conjugation is the mating of two bacterial cells during which DNA is transferred from the donor to the recipient cell. The mating process is controlled by an F plasmid, which carries the genes for the p

14、roteins required for conjugation. The most important protein is pilin, which form the sex pilus (conjugation tube).TransductionDefinition: phage-mediated genetic recombination in bacteriaResistant to environmental nucleasesTypes of transductiongeneralized - Transduction in which potentially any dono

15、r bacterial gene can be transferredrestricted - Transduction in which only certain donor genes can be transferredGeneralized TransductionInfection of DonorPhage replication and degradation of host DNAAssembly of phages particlesRelease of phageInfection of recipientLegitimate recombinationSpecialize

16、d TransductionLysogenic PhageExcision of the prophageReplication and release of phageInfection of the recipientLysogenization of the recipientHomologous recombination also possibleTransductionSignificancelysogenic conversionCorynebacterium diphtheriae Diphtheria toxinClostridium botulinum Botulinum

17、toxin transduction(转导)Transduction is the transfer of cell DNA by means of a bacterial virus (bacteriophage). During the growth of the virus within the cell, a piece of bacterial DNA is incorporated into the virus particle and is carried into the recipient cell at the time of infectionSection 4 Application of bacterial heredity and variation in medicineThe identification, treatment and preventionThe detection of cancerogenic substanceThe epidemiological surveyThe s