医学微生物学（邬国军）5生物专业-第四章：细菌的遗传与变异.ppt

Ⅲ．受体菌的生理状态 Some bacteria are able to take up DNA naturally. However, these bacteria only take up DNA at a particular time in their growth cycle when they produce a specific protein called a competence factor. The bacteria at this stage are called competent. Most bacteria are not able to take up DNA naturally. However, in these bacteria competence can be induced in vitro by treatment with chemicals (e.g. CaCl2). Ⅳ．环境因素：Ca++，Mg++，cAMP等由 于有利于维持DNA 的稳定性，故具有促 进转化的作用。 (2) 接合(Conjugation) ① 定义 通过性菌毛连接沟通，将遗传物质由供体菌转给受体菌的方式。 ② F质粒的接合 Ⅰ. F因子的基本知识 ※ 功 能—— 编码性菌毛的产生 ※ 复制方式—— 滚环复制或与宿主菌染色体整合而随 着宿主菌染色体的复制而复制。 ※ 存在形式: F+ 菌—— 包含游离F质粒的细菌 Hfr菌—— 高频重组菌 (high frequency recombinant) F 质粒整合到宿主菌基因组中. F’ 菌—— 含有游离的F’质粒（F质粒上整合了部分宿 主基因组片段） F- F+ Hfr F’ Conjugate with F+ Curing Integrate excision Deviational excision Curing Integrate Conjugate with F’ Ⅲ．Transform of E. coli F plasmid Ⅳ．F质粒接合的类型 ☆ F+×F- 接合 ☆　Hfr×F- 接合 ☆　F’×F－接合 （3）转导(Transduction) ① 定义 由噬菌体介导，将供体菌的DNA片段转入受体菌，使受体菌获得供体菌的部分遗传性状。 ② 转导的类型 Generalized transduction(普遍性转导) Transduction in which potentially any dornor bacterial gene can be transferred Restricted transduction （局限性转导） Transduction in which only certain donor genes can be transferred Ⅰ．普遍性转导(Generalized Transduction) Potentially any donor gene can be transferred The fate of exogenous DNA in Generalized Transduction i) Complete transduction (完全转导) ii) Abortive transduction (流产转导): Ⅱ．局限性转导(Restricted transduction) (Lysogenic Phage) Ⅲ．Difference between generalized transduction and Restricted transduction (discuss) Generalized Restricted Vector Target gene Time Cause Pseudophage Defective phage Any dornor gene Certain donor gene Bacteriolysis phase Lysogenic phase Error assemble Error excision (4) 溶原性转换(Lysogenic Conversion) ① 定义 溶原性转换是指侵入细菌的噬菌体在溶原期，以前噬菌体形式与细菌的染色体发生重组，导致细菌的基因