Transduction is the process in which bacterial DNA is transferred from one bacterial cell to another by means of a phage particle. There are two types of transduction, generalized transduction and specialized transduction.
- If all donor DNA fragments from any region of the chromosome have a chance to enter the transducing bacteriophage, it is known as generalized transduction.
- In this type of transduction, the bacteriophage initially infects the donor cell and begins the lytic cycle.
- When the virus enters the bacterial cell, it hijacks the host cell and synthesizes the components of the virus, such as the genome, enzymes, capsid, head, and tail fibers. The viral enzyme then hydrolyzes the host cell’s DNA into small fragments.
- During the assembly of the virus component to form progeny viruses, at some point any of the donor DNA fragments become incorporated into the virus capsid (bacteriophage head). Such an abnormal bacteriophage, when it infects a new cell, can transfer this donor DNA to new bacteria. Since this donor DNA is not viral DNA, it does not replicate within the recipient bacteria but undergoes homologous recombination with the recipient cell’s chromosomal DNA forming a recombinant cell.
What is generalized transduction?
There are two types of bacteriophages: virulent and temperate. The virulent bacteriophage is capable of killing the host bacteria. They always undergo a lytic life cycle that causes the death of the host bacteria. The infection of a bacterium by a virulent bacteriophage and the transfer of the bacterial DNA to another bacterium during the second infection is known as generalized transduction. Thus, generalized transduction can be defined as the transfer of bacterial DNA from one bacterium to another bacterium by a virulent bacteriophage during the lytic cycle of the bacteriophage.
Bacterial DNA transfer occurs due to mispackaging of the genetic material in the new phages. Packaging of newly replicated viral DNA in new phages shows low fidelity. Therefore, during the packaging of genetic material, small fragments of bacterial DNA or bacterial DNA recombined with viral DNA may be incorrectly included in the phages. If bacterial DNA is inserted into the viral capsid by chance, the second infection introduces this DNA into another bacterium. Therefore, the transduction is successfully completed between two bacteria.
After infection, virulent phages are able to control the bacterial cellular machinery to replicate their own DNA. The virus also becomes capable of degrading the bacterial chromosome into small pieces and causes sudden rupture of the bacterial cell wall to release assembled phages causing cell death.