Gene transfer is the mechanism of transferring the genetic material, DNA (deoxyribonucleic acid), from one bacteria to another. It is broadly of two types; vertical and horizontal. Vertical gene transfer involves transferring a gene from a parent to their offspring.
In a 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 into the recipient and changes the genetic composition of the recipient permanently.
Three broad mechanisms mediate the 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
- The process occurs between two living cells
- Requires mobilization of donor bacterium’s chromosome/ plasmid
- Plasmids 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 gets transferred
- For artificial genetic recombination purposes, the temperate phage is the 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 cells uptake free DNA released into the environment.
- DNA is released into the environment when another bacterial cell (i.e., donor) dies and undergoes lysis
- Not all bacteria can go for transformation; only some bacteria can take free DNA and can go through transformation. These types of bacteria are called competent bacteria.
- Pathogenic bacteria showing competence
- Haemophilus spp
- Streptococcus spp
- Neisseria spp