Gene Transfer Mechanism in Bacteria and It’s types

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.

1. Conjugation: Transfer of genes between cells that are in physical contact with one another
2. Transduction: Transfer of genes from one cell to another by a bacteriophage
3. Transformation: Transfer of cell-free or “naked” DNA from one cell to another

Conjugation

• 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

Transduction

• 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

Transformation

• 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

References

1. Holmes RK, Jobling MG. Genetics. In: Baron S, editor. Medical Microbiology. 4th edition. Galveston (TX): University of Texas Medical Branch at Galveston; 1996. Chapter 5. Available from: https://www.ncbi.nlm.nih.gov/books/NBK7908/ 
2. Sun D. (2018). Pull in and Push Out: Mechanisms of Horizontal Gene Transfer in Bacteria. Frontiers in microbiology, 9, 2154. https://doi.org/10.3389/fmicb.2018.02154