微生物学第六章教学课件【可编辑PPT】

Gene horizotal transfer (基因的水平转移）
目前来说，微生物的基因水平转移方式主要有三种： 转化 （transformation）；转导 （transduction)；
和接合转移 （conjugation)。 A, 供体(donor)：提供DNA的细菌细胞； B, 受体 (recipient)：获得DNA的细胞； C, 供体基因进入受体细胞产生的结果： （1）暂时存在于受体细胞中，在细胞分裂过程中被丢
Gene transfer by this process occurs in soil and marine environments and may be an important route of genetic exchange in nature.
Artificial transformation is carried out in the laboratory by a variety of techniques, including treatment of the cells with calcium chloride, which renders their membranes more permeable to DNA. This approach
DNA Transformation （转化）
• 转化（transformation)：
•
受体菌直接吸收供体菌的DNA片段而获得后
者部分遗传性状的现象。
转化子（transformant）:
Βιβλιοθήκη Baidu
通过转化方式而形成的杂种后代称为转化子。
感受态（competence）:
受体细胞最易接受外源DNA片段并能实现转
微生物学第六章教 学课件
重点和难点
1，细菌的基因水平转移方式； 2，转座，转座子的类型及其遗传效应。
Oswald T. Avery and his colleagues then set out to discover which constituent in the heat-killed virulent pneumococci was responsible for Griffith’s transformation. These investigators selectively destroyed constituents in purified extracts of virulent pneumococci, using enzymes that would hydrolyze DNA, RNA, or protein. Transformation of the nonvirulent bacteria was blocked only if the DNA was destroyed, suggesting that DNA was carrying the information required for transformation. The publication of these studies provided the first evidence that Griffith’s transforming principle was DNA and therefore that DNA carried genetic information.
化的一种生理状态。
转化过程
When bacteria lyse, they release considerable amounts
of DNA into the surrounding environment. These
fragments may be relatively large and contain several genes. If a fragment contacts a competent (感受态） cell, one able to take up DNA and be transformed, it can
be bound to the cell and taken inside.
当细菌裂解后，它们向环境中释放大量的DNA。其 中的某些DNA片段相对比较大，含有多个基因。如 果其中一个片段与感受态细胞接触，后者就会与之 结合，并将其转移到细胞内。
The transformation frequency of very competent cells is around 10-3 for most genera when an excess of DNA is used. That is, about one cell in every thousand will take up and integrate the gene. Competency is a complex phenomenon and is dependent on several conditions.
失； （2）整合到受体细胞基因组中； （3）外源基因置换受体中的部分基因。
DNA Transformation （转化）
One way in which DNA can move between bacteria is through transformation, discovered by Fred Griffith in 1928. Transformation is the uptake by a cell of a naked DNA molecule or fragment from the medium and the incorporation of this molecule into the recipient chromosome in a heritable form. In natural transformation the DNA comes from a donor bacterium. The process is random, and any portion of a genome may be transferred between bacteria.