Transduction

Transduction

Transduction is an event in which bacteriophages function as vectors/
vehicles to transfer of DNA from donor bacteria to recipient bacteria.  
Transfer of bacterial genes by phage was discovered by Zinder and  
Lederberg in 1952 in Salmonella typhimurium. Transduction  
mechanism is occur in two ways.
1. Generalized transduction
2. Specialized transduction
The bacteriophage containing the bacterial DNA of donor is called  
transfusing phage. Bacteriophages are two types.
i) Virulent phage: Virulent phage follow lytic cycle capable of causing  
bacterial infection and eventually destruction and death of bacterial  
cell e. g. T4 Phage
ii) Temperate phage: Phage does not cause disruptic infection instead  
phage DNA incorporated into bacterial DNA and replicate Lysogenic  
and after sometime become virulent cause lysis. e. g. λ phage  
1. Generalized transduction: In generalised transduction, a DNA  
fragment is transferred from one bacterium to another by a lytic  
phage which carry donor bacterial DNA due to an error virulent phage  
act as vehicle for transduction.

 

Steps of generalised transduction

  

i) A lytic bacteriophage infect susceptible bacterium

ii) When phage genome enter the bacterium it cause  
degradation of bacterial host DNA into fragments.
iii) Phage genome replicate using host machinery and  
synthesise enzyme and coat protein.
iv) During maturation and packaging of virus particles,  
few phage heads may envelope fragments of bacterial  
DNA by error that is double stranded so only bacterial  
DNA(host) is present in the transducing phage.
v) Transducing phage carrying bacterial DNA (host) or  
donor will infect another cell and transfer the donor  
DNA to the recipient bacterial cell.
vi) When bacterial DNA of donor is introduced into the  
host cell, It can be integrated into the bacterial  
chromosome of host and transfer several bacterial gene
at one time forming Recombinant DNA.
vii) Bacteria (recipient cell) multiply with new genetic  
material.
Examples of Generalised transduction is P1 in E. coli  
and P22 in Salmonella.
 

Generalised transduction may be three types

 

2. Specialized transduction: 

 

A temperate phage infect a susceptible donor bacterium and its DNA into its genome. It is called
Prophage.
•A DNA fragment is transferred from one bacterium to another by a temperate bacteriophage  which carry donor DNA along with phage genome due to an error.  
•In specialised transduction phage insert in genome at donor at specific site and  
perform site specific recombination.  
•Specialised transduction only occur when lysogenic (temperate) infected donor bacteria enter lytic cycle and release phage progeny. They only bacterial genes that can be transduced are very near to the site at which prophage is integrated.  
•The only site at which λ phage integrate is between for galactose formation (gal gene) and biotin  synthesis gene (bio gene), so at the time of abnormal integration of prophage only gal or bio gene could be transferred.