In Transduction, DNA is transferred from one cell to another through the agency of viruses. Genetic transfer of host gene by bacteriophage occurs in two ways-Generalized transduction and specialized transduction.
Specialized transduction occurs only in some temperate phages. But specialized transduction is an extremely efficient gene transfer mechanism.
In some occasions, DNA from a specific region of the host chromosome is integrated directly into the virus genome-usually replacing some viral genes. The resulting defective transducing phage (temperate phage) particles now have bacterial DNA as a part of genome.
To understand the process of specialized transduction, you must first be aware about lytic cycle of Bacteriophage.
Let’s contrast between normal lysogenic cycle and mechanism of transduction
- When a bacterial cell is lysogenized by a lambda phage, the phage genome becomes integrated into the host DNA at a specific site.
- Viral DNA replicates under host control
On induction: The viral DNA separates from the host DNA by a process that is reverse of integration.
- During normal event: Lambda DNA is excised as a unit
- During rare event. lambda phage excise incorrectly; some of the adjacent bacterial genes are also excised along with phage DNA where as some phage DNA is left behind. These phage are called defective lambda phage.
- When the lysate containing both defective lambda phage are mixed with sensitive bacterial population, there are two possibilities
- The bacterial DNA may be integrated into the host chromosome during lysogenization, and
- The DNA may be replicated in the recipients as part of a lytic infection
Transduction has been found to occur in a variety of bacterial populations including:
- Escherichia coli
- Pseudomonas spp
- Salmonella spp
- Staphylococcus spp