人卫7版微生物chapter4,5细菌的遗传与变异

1、chapter 5 bacterial genetics and variationresulted from gene alteration (irreversible) caused by the environmental conditions (reversible) shape and structure variation colony variation菌落变异菌落变异 antigenicity variation抗原性变抗原性变异异 virulence variation毒力变异毒力变异 resistant variation耐药性变异耐药性变异vibrio cholerae（

2、霍乱弧菌）（霍乱弧菌）normal l form bacillus anthracic (炭疽杆菌炭疽杆菌), bacillus proteus (变形杆菌变形杆菌)smooth光滑型光滑型rough粗糙型粗糙型 virulent strain of bovine tubercle bacilli inoculate special media (bile胆汁胆汁, glycerine甘油甘油 , potato)cultureattenuated bacillus calmette and guerin (bcg) 13 years (230 generations) produce toxi

3、ndiphtheria bacilliatoxic diphtheria bacillitoxigenic diphtheria bacilli outline1. genetic materials of bacteria2. bacteriophage (chapter 4) 3. gene transfer and recombination 4. gene mutation5. significance of bacterial genetic variationdna forms: ds-dna, circlecharacteristics of bacterial chromoso

4、me nucleoid a circular, double-stranded molecule of dna 4.6106bp, 4000 genes no introns in structure gene neednt post transcription cleavage most of the dna for encoding protein only a few overlapping genes operon (操纵子), regulon (调节子) electron micrograph of an e.coli dnaan e. coli bacillus was treat

5、ed with an enzyme to weaken its wall, then placed in water, causing itsdna to leak out.(16,000)1.plasmids are small, usually circular，extrachromosomal, double-stranded dna molecules.2.they are capable of self-replication3.contain genes that confer some properties，such as antibiotic resistance，virule

6、nce factors.4.plasmids are not essential for cellular survival.5.conjugative (接合性) and nonconjugative (非接合性)6.compatibility (相容性) and incompatibility (不相容性)phenotypic effects1.fertility致育 plasmid (f factors)2.resistance耐药性 plasmid (r factors)3.virulence 毒力plasmid4.bacteriocin细菌素 plasmid5.metabolic p

7、lasmid definition: 转座因子转座因子 segments of dna that are able to move from one location to another from one chromosome to another from one location to another on the same chromosome between chromosome and plasmid properties of transposable elements“random” movementnot capable of self replicationtranspos

8、ition mediated by site-specific recombination (transposase, 转座酶)two major classes: insertion sequence, is (插入序列) transposon, tn (转座子): elements that carry no other genes except those involved in transpositionmutationplasmid insertionphase variationtransposaseabcdefggfedcbab. transposon (tn)（转座子）（转座子

9、）: transposable genetic elements that carry one or more other genes in addition to those which are essential for transpositionis isresistance gene(s)is isresistance gene(s)(chapter 4) bacteriophage definition shape, structure and chemical components virulent phage temperate phage obligate intracellu

10、lar parasites that multiply inside bacteria by making use of some or all of the host biosynthetic machinery ( i.e. viruses that infect bacteria).shapes of bacteriophage tadpole (蝌蚪形蝌蚪形) spheral (球形) filamentous (丝状)bacteriophagetailtail fibersbase plateheadcontractile sheathcapsiddnacomposition and

11、propagationtypes of bacteriophages lytic or virulent毒性毒性phage: phages that can only multiply within bacteria and kill the cell by lysis. lysogenic溶原性溶原性 or temperate温和性温和性 phage: phages that can either multiply via the lytic cycle or enter a quiescent state in the bacterial cell and express most pha

12、ge genes through gene integration. 毒性噬菌体毒性噬菌体 lytic phage definition: phages which can only multiply within bacteria and kill the cell by lysis at the end of the life cycle.1. adsorption 吸附 2. penetration 穿入 3. biological synthesis 生物合成 4. maturation and release 成熟和释放 温和噬菌体温和噬菌体 溶原性噬菌体溶原性噬菌体 phages

13、that can either multiply via the lytic cycle or enter a quiescent state (the prophage (前噬菌体) state) in the bacterial cell and express most phage genes through gene integration. 溶原性细菌溶原性细菌 bacteria carrying prophages (前噬菌体) are termed lysogenic (溶原的) because a physiologic signal can trigger a lytic c

14、ycle resulting in death of the host cell and liberation of many copies of the phage.lysogenic bacteriumlysogenic bacteriumprophagelysogenic phage /temperate phage cycles of temperate phage lysogenic cyclelytic cycle the phage dna integrates into the cell dna it can change a nonpathogenic organism in

15、to a pathogenic onestreptococcus pneumoniae injectionisolation and culture(dead)(dead)recipientadhesionuptakebinary fissionmutant strainrecombinationtransforming principle 转化因子转化因子（突变株）（突变株）factors affecting transformationdna size: smaller than1020 genescompetence of the recipientthe ability to take

16、 up dna from environment is called competence. competence state can occur naturally or be induced artificially.(cacl2)bacterial transformationwith dna fragments the donor the recipient bacterial conjugation is the transfer of genetic material between bacterial cells by direct cell-to-cell contact or

17、 by a bridge-like connection (the sex pilus) between two cells. during conjugation the donor cell provides a conjugative or mobilizable genetic element that is most often a plasmid （质粒）or transposon（转座子）. conjugation 接合接合 f f+ +f ff f+ +f f- -f f+ +f f- -f f+ +f f+ +f f+ +f f+ +donor (供体菌)recipient

18、(受体菌)mechanism of f+ x f- crossescharacteristics of f+ x f- crosses f- becomes f+ while f+ remains f+ dna is replicated through rolling circle replication (滚环式复制) low transfer of donor chromosomal geneshfr (high-frequency recombination) bacteria 高频重组菌高频重组菌 occasionally, the f factor integrates into

19、a random position in the bacterial chromosome. when this happens, the bacterial cell is called hfr instead of f+. hfr bacteria are still able to initiate conjugation with f- cells, but the outcome is completely different from conjugation involving f+ bacteria.f+hfrintegrated (hfr)mechanism of hfr x

20、f- crosseshfrf-hfrf-hfrf-hfrf-（hfr 与 f菌杂交）菌杂交）characteristics of hfr x f- crossesnf- rarely becomes f+ while hfr remains f+nhigh frequency transfer of certain donor chromosomal geneshfrhfr中的中的f f质粒可从染色体上脱离下来，终止质粒可从染色体上脱离下来，终止hfrhfr状态，从染色体上脱离的状态，从染色体上脱离的f f质粒有时可带有染色质粒有时可带有染色体上几个邻近的基因，这种质粒称体上几个邻近的基因，这

21、种质粒称f f质粒，带有质粒，带有f f质粒的细菌为质粒的细菌为f f菌。菌。ff菌菌hfrfffff（性导）（性导）fffffffffff f- -fff f- -structure of r factors rtfresistance transfer factor耐药传递因子conjugative plasmidtransfer genestn 9tn 21tn 10tn 8rtfr determinant r determinantresistance determinant耐药决定因子transposons transduction（转导）（转导） is virus-mediated

22、 transfer of genetic information from donor to recipient cell. there are two types of transduction: generalized transduction (普遍性转导)specialized (restricted) transduction (局限性转导)完全转导完全转导流产转导流产转导generalized transductiongeneralized transductionby bacteriophages excision of the prophage replication and

23、release of phage infection of the recipient lysogenization of the recipientnormal isolationbreakageconnect breakageconnect deviation isolationspecialized transductionby a temperate bacteriophage the added genetic information provided by the dna of a prophage may enable a bacterium to possess new gen

24、etic traits. for example, some bacteria become virulent only when infected themselves with a specific temperate phage. produce toxindiphtheria bacilliatoxic diphtheria bacillitoxigenic diphtheria bacilli protoplast fusion 原生质体融合原生质体融合 definition: protoplast fusion is a physical phenomenon. during fusion two or more protoplasts come in contact and adhere with one another either spontaneously or in presence of fusion inducing agents. protoplast fusion by proto