Chapter 5 Genetic Analysis in Bacteria

Chapter 5 Genetic Analysis in Bacteria and Bacteriophages 第五章细菌与噬菌体遗传

structure of bacterial genomes

mechanisms by which bacteria transfer genes

between cells of the same species

mechanisms by which bacteria transfer genes

between bacterial cells and bacterial viruses

Geneticists can use their knowledge of bacterial genetics in general and of various forms of bacterial gene transfer in particular to identify, map, and characterize the genes that contribute to biological process.

5.1 Plasmid patterns 质粒类型

5.2 Transfer of genes between bacteria 细菌间基因的传递

5.2.1 Transfer by conjugation （结合传递）

5.2.2 Three transfer types (F+, F-, Hfr, F’ cells)

5.2.3 Interrupted mating experiment – 中断杂交技术

5.3 Transfer of genes between bacterium and bacterial

viruses 细菌与噬菌体间基因的传递

5.3.1 Bacteriophage and its properties

5.3.2 Generalized transduction （普通转导）

5.3.3 Specialized transduction （特定转导）

5.3.4 Recombination in bacteria

Advantages ：

1. Rapid reproduction, short life-span and large amount

2. Small genetic material, simple cell structure

3. Simple DNA structure, naked, helix and circular

DNA

4. Monoploid DNA

Plasmids are chromosome-like structures found in bacterial cells, but which are not essential to bacteri

al growth.

Some can move from one bacterium to another. The best studied is the F plasmid. This is an episome, an element that can replicate either independently or

integrate into the bacterial chromosome.

5.1 Plasmid patterns

E.coli encodes all the enzymes it needs for amino-acid and nucleotide biosynthesis, it can grow in minimal media, which contain glucose as the only source of carbon and energy, and inorganic salts as the source of the other elements that compose bacterial cells.

遗传物质的分布：

E.coli: 大环 DNA 主染色体 4×106bp

质粒小染色体，大环 DNA 的 0.5%~2% ，

约 4000~5000bp

infectious ： from donor strain to recipient 从一个细菌（供体菌）转移到另一个不含质粒的受体菌中

non-infectious: 不能传递

replicable: isolated from chromosome 独位于染色体之外 combined: integrated into main chromosome and disengaged again 插入到主染色体上 , 条件改变可脱离

F plasmid: F+ - 供体菌 ( 雄性菌 ), 膜上有性须 , 可转移

F- - 受体菌 ( 雌性菌 ), 无性须

R plasmid: antibiotic resistance ( 抗药性质粒 )

Plasmid pattern

5.1 Plasmid patterns 质粒类型5.2 Transfer of genes between bacteria 细菌间基因的传递 5.2.1 Transfer by conjugation （结合传递） 5.2.2 Three transfer types (F+, F-, Hfr, F’ cells)

5.2.3 Interrupted mating experiment – 中断杂交技术5.3 Transfer of genes between bacterium and bacterial

viruses 细菌与噬菌体间基因的传递 5.3.1 Bacteriophage and its properties

5.3.2 Generalized transduction （普通转导） 5.3.3 Specialized transduction （特定转导） 5.3.4 Recombination in bacteria


5.2 Transfer of genes between bacteria

Focus on E.coli: the most studied and best understood species of bacteria is E.coli, a common inhabitant of vertebrate intestines. E.coli cells can grow in the complete absence of oxygen—the condition found in the intestine

s.


( 营养缺陷型菌原养型完全培养基 )

Strain A: met- bio- thr+ leu+ thi+

Strain B: met+ bio+ thr- leu- thi-

Minimal medium

A met- bio- thr+ leu+ thi+

B met+ bio+ thr- leu- thi-

met+ bio+ thr+ leu+ thi+

colonies

Founded by electronic microscope:

Conjugation tube produced between two strains

A

B

Streptomycin ( 链霉素 ) treatment

on A and B separately

A x BRestrainedreproduction

colonies

A x B

Restrained

reproduction

no colony

A B

donor strain recipient

F+ F-






5.3 Transfer of genes between bacterium and bacterial







5.2.2 Three transfer types:

1) 游离态 F 质粒

F+ F-

• Low recombination between main chromosome 主染色体之间重组率低 • F- F+

flash

2) 结合态 F 质粒

F+ integrated into mainDNA (Hfr strain)

F-

• HIGH cross-overs and recombination betwe

en main DNA

• F- F-

flash

F-Hfr

3) F’ 质粒

When the F plasmid is excised from the bacterial chromosome it sometimes incorporates part of the chromosome into its own structure - F’

Hfr 菌株质粒从主染色体脱离时携带部分主染色体基因形成的游离质粒 - F’

flash

• Hfr F’ F- F’ integration –sexduction ( 性导 )

• Low frequency

• F- F’ Hfr

F’

1)

2)

3)

Interactive genetics – problem2

Applications:

C Strain: arg-met+ × E Strain: arg+met-

arg +met+

F+ × F+ Hfr× F- Hfr× F+

F- × F- F+ × F- Hfr× Hfr

What type of crosses would give you many/few/no exconjugants?

C Strain: arg-met+ × E Strain: arg+met-

arg +met+

F+ × F+ Hfr× F- Hfr× F+

F- × F- F+ × F- Hfr× Hfr

What type of crosses would give you many/few/no exconjugants?

FOOFOC5

OFMOFC4

FOOFOC3

MOOMOC2

OFMOFC1

E5E4E3E2E1

Possible crosses between strains below, identify which strains are F+, F- and Hfr cell

O= none; F=few; M= many exconjugants

FOOFOF+

OFMOFF-

FOOFOF+

MOOMOHfr

OFMOFF-

F-F+HfrF-F+

Possible crosses between strains below, identify which strains are F+, F- and Hfr cell

O= none; F=few; M= many exconjugants





5.2.3 Interrupted mating experiment – 中断杂交技术5.3 Transfer of genes between bacterium and bacterial







In the chromosome, plasmid can cause transf

er of the entire chromosome to a recipient cell.

The time at which each gene enters the recipient

can be used to create a gene map.

5.2.3 Interrupted mating experiment – 中断杂交技术 - by E. Wollman and E. Jacob in 1957

Hfr ×F- 隔时取样振荡中断杂交

接种 ( str. included to kill Hfr) strr F- genotype

9’ azir 11’ tonAr 18 lac + 25’ gal +

Hfr strain (strs azir tonAr gal + lac +)

F- (strr azis tonAs gal- lac-)

min

%

O azi tonA lac gal F

9 11 18 25

gene order and mapunit in Hfr cell

Application:

Hfr strains Transfer order of genes

H

1

2

3

AB312

0 thr pro lac pur gal his gly thi

0 thr thi gly his gal pur lac pro

0 pro thr thi gly his gal pur lac

0 pur lac pro thr thi gly his gal

0 thi thr pro lac pur gal his gly

• Draw the structure of main DNA

• Mark the transfer origin and the direction on it

• Mark the random integrated positions of F plasmid

H thr 1thi

gly

his

gal 3

pur

lac

pro

2AB312

H 1 2 3 AB312

0 thr pro lac pur gal his gly thi0 thr thi gly his gal pur lac pro0 pro thr thi gly his gal pur lac0 pur lac pro thr thi gly his gal0 thi thr pro lac pur gal his gly






5.3 Transfer of genes between bacterium and bacterial viruses

细菌与噬菌体间基因的传递 5.3.1 Bacteriophage and its properties






Phages can be divided into two classes: virulent or temperate depending on how they behave after infection of a bacteriu

m.

when a virulent phage infects a bacterium it takes over the synthetic machinery of the host and uses it as a factory for the p

roduction of new phages.

5.3 Transfer of genes between bacterium and bacterial viruses

Temperate phages have a choice between the lytic ( 溶菌 ) and an alternative lysogenic ( 溶原 ) pathway.

The latter involves integration into the host’s chromosome where the phage, now termed a prophage ( 原噬菌体 ), is dormant and replicates along with the rest of the host chrom

osome.

Occasionally with low frequency the prophage loses its dormancy and converts to the lytic, replicating phages and lysi

ng the bacterium.

( 二 ) 转导作用 t r a n s d u c t i o n

病毒、噬菌体介导溶菌途径溶原菌途径

ÁÑ½â

ÈÜÔ

溶原 / 菌过程

5.3.2 Generalized transduction （普通转导）Bacteriophages are involved in transduction. Virulent phages replicate in the bacterium. An occasional phage particle will contain a small fragment of bacterial DNA rather than bacteriophage DNA. The bacteriophage will transfer it to a recipient cell

- generalized transduction

侵染复制宿主 DNA 断裂噬菌体 DNA

组装外壳，宿主 DNA 碎片随机装入子噬菌体释放带有原宿主 DNA 基因侵染细菌

原宿主 DNA 片段与受体菌同源互补部分二倍体形成或发生交换重组 - 普通转导 .


Lysogenic prophage loses its dormant state and excised from the host DNA. Rarely the excision process is inaccurate, the phages carry and transfer host genes betwee

n bacteria – specialized transduction

结合态噬菌体切离宿主 DNA ，携带部分宿主基因，再次侵染时与受体菌 DNA 同源互补及交换重组。


• Transformation - 转化

细菌细胞从周围介质吸收不同基因型细胞的 DNA ，其基因型和表型发生改变的过程

• Transfection – 转染

用除去蛋白质外壳的病毒核酸感染细胞或原生质体的过程。转化的一种特殊形式

• Transduction – 转导

以噬菌体为媒介，将细菌基因导入另一细菌的过程。普通转导、特定转导

Documents

Chapter 5 Genetic Analysis in Bacteria