Bacterial changeability. Recombination and Mechanism of DNA transfer between bacterial cells.
Genetic variability in bacteria results from spontaneous mutations and recombination processes. DNA changes in bacteria include accidental mutations and horizontal gene transfer between donor and recipient cells, followed by recombination. These changes help bacteria adapt to unfavourable conditions and contribute to bacterial evolution.
Recombination
- Recombination is the incorporation of foreign (extrachromosomal) DNA into the chromosome or plasmid.
- Donor DNA must integrate into the recipient genome to be stable and expressed in progeny.
- It can occur between bacterial chromosomes, viral DNA, or involve the integration of phages/plasmids into the chromosome.
- Homologous (Legitimate) Recombination:
- Occurs between closely related DNA sequences.
- Generally substitutes one sequence for another, often by crossing-over.
- Requires a set of enzymes, the most important being the RecA enzyme.
- Common in closely related bacteria.
- Non-homologous (Illegitimate or Site-specific) Recombination:
- Occurs between dissimilar (non-homologous) DNA sequences.
- Generally produces insertions, deletions, or both.
- Often requires specialised recombination enzymes produced by transposons and lysogenic bacteriophages.
- Does not require DNA sequence similarity for integration or excision.
- Involves transposons and temperate phages (e.g., λ phage).