chapter6 microbial genetics

降解质粒
将复杂的有机化合物降解成能被其作为碳源和能源利用的简单 形式，环境保护方面具有重要的意义。
假单胞菌： 具有降解一些有毒化合物，如芳香簇化合物(苯)、农药
辛烷和樟脑等的能力。 TOL质粒：含分解甲苯的基因； CAM-OCT质粒：含分解樟脑辛烷的基因
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(5) 毒性质粒（virulence plasmid）
失去形成芽胞能力, 毒性降低
变形杆菌（H） 1%石炭酸
迁徙生长
鞭毛变异
单个菌落（O）
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二、菌落变异

在陈旧培养基中型菌落 R
失去LPS的特异性多糖重复单位 同时伴有其他性状的改变
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三、毒力变异

β棒状噬菌体
白喉棒状杆菌
获得白喉毒素
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毒性质粒（virulence plasmid）
代谢质粒（Metabolic plasmid）
隐秘质粒（cryptic plasmid）
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(1) 致育因子(Fertility factor，F因子)
又F称因F子质能粒以，游其离大状小态约(F1+0)0和kb，这是最早发现的一种与大肠杆菌 的有以性与生染殖色现体象相（结接合合的作状用态）有关的质粒。
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(6)隐秘质粒（cryptic plasmid）
隐秘质粒不显示任何表型效应，它们的存在只有通过物理的 方法，例如用凝胶电泳检测细胞抽提液等方法才能发现。
它们存在的生物学意义，目前几乎不了解。
在应用上，很多隐秘质粒被加以改造作为基因工程的载体 （一般加上抗性基因）
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2μm质粒
大多数酵母菌含有一种称为2μm的质粒 ，属隐秘质粒
细菌素
抗生素

WORKING GLOSSARY
Auxotroph an organism that has developed a nutritional requirement through mutation Cloning vector genetic element into which genes can be recombined and replicated Conjugation transfer of genes from one prokaryotic cell to another by a mechanism involving cell-to-cell contact and a plasmid Diploid a eukaryotic cell or organism containing two sets of chromosomes Electroporation the use of an electric pulse to induce cells to take up free DNA Gene disruption use of genetic techniques to inactivate a gene by inserting within it a DNA fragment containing an easily selectable marker. The inserted fragment is called a cassette, and the process of insertion, cassette mutagenesis
Section 2. Techniques of bacterial genetics: in vivo
In vivo : manipulate the genetic material within the organism

• Vaccinia virus is known to show resistance to the antiviral effects of interferons.
• One of the early genes of this virus, K3L, encodes a protein which is homologous to eIF-2 which inhibits the action of PKR. In addition, the E3L protein also binds dsRNA & inhibits PKR activation
• This is only possible for viruses which are genetically variable, e.g. influenza virus & HIV.
• Herpesviruses use alternative strategies such as encoding viral Fc receptors to prevent Fc-dependent immune activation.
© Academic Press, 2000.
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Chapter 6: Infection
The Skin:
• Mammalian skin is a highly effective barrier against viruses.
• The outer layer (epidermis) consists of dead cells & therefore does not support virus replication.
• Poxviruses can also inhibit C9 polymerization, preventing membrane permeabilization.

Mendel
• Born
Johann Mendel孟德尔in 1822 – Took name of Gregor孟德尔 as a monk（道名） Mendel was a member of a monastery修道院in what is now the Czech Republic（捷克共和国） Studied physics and botany植物学in the University of Vienna维也纳(1851-1853) Began first hybridization杂交experiments on the garden pea豌豆in 1856 Research ended in 1868 when promoted to abbot (修道院院长)
Major advantages of classical genetic approach
○ Mutants can be isolated and characterized without any a priori （以前的）understanding of the molecular basis of the function.
Dominant显性的: An allele which is expressed (masks the other).
Recessive:隐性An allele which is present but remains unexpressed (masked) Homozygous:纯合子Both alleles for a trait are the same. Heterozygous:杂合子The organism's alleles for a trait are