Bacterial Genetics: Mechanism of Specialized transduction

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

  1. When a bacterial cell is lysogenized by a lambda phage, the phage genome becomes integrated into the host DNA at a specific site.
  2. Viral DNA replicates under host control
  3. On induction: The viral DNA separates from the host DNA by a process that is reverse of integration.
    1. During normal event:  Lambda DNA is excised as a unit
    2. 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.
    3. When the lysate containing both defective lambda phage are mixed with sensitive bacterial population, there are two possibilities
      1. The bacterial DNA may be integrated into the host chromosome during lysogenization, and
      2. 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:

  1. Escherichia coli
  2. Pseudomonas spp
  3. Salmonella spp
  4. Staphylococcus spp

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