In bacterial population DNA can be transferred from one organism to another by the horizontal transfer mechanism (apart from vertical inheritance). The DNA thus transferred by lateral/horizontal method can be stably incorporated in the recipient , and changes the genetic composition of recipient permanently.
Three broad mechanisms mediate efficient movement of DNA between cells- conjugation, transduction and transformation.
- Conjugation: Transfer of genes between cells that are in physical contact with one another
- Transduction: Transfer of genes from one cell to another by a bacteriophage
- Transformation: Transfer of cell-free or “naked” DNA from one cell to another
- Conjugation was the first extensively studied method of gene transfer
- Conjugation requires donor cell-to-recipient cell contact and is mediated by sex pilus
- Process occurs between two living cells
- Requires mobilization of donor bacterium’s chromosome/ plasmid
- Plasmid are genetic elements most frequently transferred by conjugation
- Phage mediated genetic recombination in bacteria i.e. phage is used to transfer DNA from one bacterium to another
- Transducing particle: Bacterial nucleic acid in phage coat
- There are two broad categories of Transduction
- Generalized transduction: Where virtually any genetic marker can be transferred
- Specialized transduction: Bacterial DNA who are adjacent to viral DNA in the prophage get transferred
- For artificial Genetic recombination purpose Temperate phage are preferred vehicle for gene transfer
- Transduction has been found to occur in a variety of bacterial populations including:
- Escherichia coli
- Pseudomonas spp
- Salmonella spp
- Staphylococcus spp
- Recipient cell uptake free DNA released into the environment.
- DNA is released it to the environment when another bacterial cell (i.e. donor) dies and undergoes lysis
- Not all bacteria are able to go for transformation, only some bacteria are able to take free DNA and are able to go transformation. These type of bacterial are called competent bacteria.
- Pathogenic bacteria showing competence
- Haemophilus spp
- Streptococcus spp
- Neisseria spp