Introduction
Transduction is a process of horizontal gene transfer in bacteria, where genetic material is transferred from one bacterium to another using a bacteriophage (a virus that infects bacteria). There are two main types of transduction: generalized and specialized. Both are important mechanisms for genetic variation in bacterial populations.
1. Generalized Transduction
Definition
Generalized transduction occurs when a bacteriophage accidentally incorporates a random fragment of the host bacterium’s DNA during the lytic cycle.
Process
- In the lytic cycle, the phage replicates and breaks down the host bacterial DNA.
- Sometimes, fragments of bacterial DNA are mistakenly packaged into phage heads instead of viral DNA.
- These defective phages can infect another bacterium and inject bacterial DNA.
- The foreign DNA may recombine with the new host’s genome, leading to gene transfer.
Features
- Any gene from the bacterial chromosome can be transferred.
- Does not require integration at a specific site.
- Used for bacterial gene mapping.
2. Specialized Transduction
Definition
Specialized transduction occurs when a temperate phage (like λ-phage) integrates its genome into a specific site in the bacterial chromosome and later excises incorrectly, carrying adjacent bacterial genes with it.
Process
- Occurs during the lysogenic cycle.
- The phage DNA integrates at a specific site in the bacterial genome (e.g., between gal and bio genes).
- During excision, nearby bacterial genes are picked up along with phage DNA.
- Only genes near the site of integration can be transferred.
Features
- Only specific genes are transferred.
- Requires temperate phages.
- Less commonly used for mapping due to limited gene range.
Comparison Table
| Feature | Generalized Transduction | Specialized Transduction |
|---|---|---|
| Type of Phage | Lytic | Temperate (Lysogenic) |
| Genes Transferred | Any random gene | Only specific nearby genes |
| DNA Packaging Error | Random fragments of host DNA | Incorrect excision of integrated phage |
| Applications | Gene mapping, genetic research | Gene regulation studies |
Conclusion
Both generalized and specialized transduction are essential for genetic diversity in bacterial populations. While generalized transduction allows random gene transfer, specialized transduction is limited to specific genes. These processes are widely studied in genetic engineering and microbiology research.