Recombination in bacteria

By. Pandya Dilip

Cug/2014/1078

Gene transfer in becteria

• transfer genetic material from one becteria to another becteria

• In bacteria genetic transfer can happen three ways:– Transduction– Conjugation– transformation

Transduction

Transduction

• Definition: gene transfer from a donor to a recipient by way of a bacteriophage

• Discover by lederberg & zinder in 1951

• Bacteriophage (phage): A virus that infects bcteria

Bacteriophage - structure

Types of Bacteriophage

• Bacteriophages have been classified into two types on the basis of their interaction with a bactria cell.

1. Virulent phages. 2. Temperate phages.

• Virulent – always multiply & lyse the host cell after infection.

• Temperate phage: That have a choice between two life-style after infection.

1.Lytic cycle 2.lysogenic cycle

• 1. Lytic cycle = they reproduce & lyse their host cell just like virulent phages.

• Lysogenic cycle = their chromosome are integrated in to the chromosome of the host.

Transduction

• Types of transduction1. Generalized - Transduction in

which potentially any donor bacterial gene can be transferred.

2. Specialized- Transduction in which only certain donor genes can be transferred

Generalized transduction

• Starts with the LYTIC CYCLE where a T- even phage infects E. coli killing the host cell, and synthesizing >100 copies of itself.

• The T-even phage randomly packages bacterial DNA in a few defective phages.

• Once a T – even phage infects another E. coli, this genetic information can be recombined into the host cell without causing the lytic cycle.

• New genetic information is thereby transduced from one bacteria to another.

Generalized Transduction

Specialized Transduction

• In specialized transducing particle carries only specific portions of the bacterial genome.

• Specialized transduction by a temperate bacteriophages which chromosome are able to integrate at a specific attachment site on host chromosome.

• Phages chromosome & bacterial chromosome is a attach specific attachment site by a covalently in prophages.

• The gal transducing phage (lambda) makes ~ 2,000 copies of itself with the gal gene, and infects other E.coli.

• When gal integrates into the nucleoid of other E. coli, it may provide these bacteria with a new capacity to metabolize galactose.

• The best-studied example of specialized transduction is the lambda phage. The lambda genome inserts into the host chromosome at specific locations known as attachment or att sites.

• The phage att sites and bacterial att sites are similar and can complex with each other.

conjugation

• Bacterial conjugation is the transfer of genetic material (plasmid) between bacterial cells by direct cell-to-cell contact or by a bridge-like connection between two cells.

• Discovered in 1946 by Joshua Lederberg and Edward Tatum,

BACTERIA A BACTERIA B

Transfer of genetic material from bactria A to bacteria B by physical

contact is called conjugation.

Who is donor ?

F plasmid absent donor recipient F + F- Male cell femal cell

What happen during conjugation

What is Hfr cell?

• When F factor/ plasmid exists in an integrated state with the host chromosome

Hfr conjugation