VMC 211: General Veterinary Microbiology (1+1)

TRANSDUCTION

• It is the transfer of a portion of DNA from one bacterium to another by bacteriophage.
• Phages exhibit two types of replication, lytic and lysogenic. In lytic mode after entering into the bacteria they direct the synthesis of phage genomes and proteins which assemble to produce new phages. The newly formed phages are then released by lysing the bacterial cell.
• In lysogenic mode carried out by temperate phages they have their DNA like an episome in bacteria. This viral DNA can be integrated in the bacterial chromosome. Such DNA are known as prophages.
• The bacteria having prophages can be induced by UV light and other agents to make the prophages to replicate rapidly and go through lytic cycle of growth. This leads to lysis of cells and release of virus particles.
• The phages particles may have some bacterial DNA incorporated or in some phages there will be only bacterial DNA. When such phage infects another bacterium the bacterial DNA in then is transferred to the recipient bacterial cell.
• This DNA transfer mechanism was found out by Zinder and Lederberg in 1952 when studying sexual recombination in Salmonella.

Generalized transduction

• All fragments of bacteria DNA have a chance to enter in to the phage in generalized transduction.
• Any part of the bacterial chromosome may be incorporated in to the phage head during assembly and it is usually not associated with any viral DNA.

Specialized transduction

• In this process the phages transduce only those bacterial genes adjacent to the prophage in the bacterial chromosome. This process is also called as restricted transduction.
• When such a phage infects a bacterium it carries with it certain bacterial genes which have become part of phage genome.
• The bacterial genes carried in the phage genome can then recombine with the homologous DNA of the infected cell.

Illustration for transduction