transduction
Summary
Transduction is a mechanism of horizontal gene transfer in bacteria in which a bacteriophage (virus) transfers DNA from one bacterium to another. It comes in two forms: generalized transduction (random bacterial DNA packaged into phage) and specialized transduction (specific DNA adjacent to phage integration site is transferred). This process is a key mechanism of antibiotic resistance and virulence factor spread among bacteria.
Detail
Transduction occurs when a bacteriophage infects a bacterial cell (the donor) and, during the process of viral replication and packaging, incorporates bacterial DNA into the phage capsid instead of or along with viral DNA. When this phage subsequently infects a new bacterium (the recipient), it introduces the donor bacterial DNA, which can then be incorporated into the recipient's genome via recombination.
Generalized transduction occurs during the lytic cycle when the phage's packaging machinery mistakenly incorporates random fragments of bacterial chromosomal DNA into the phage head instead of viral genome, due to imprecise packaging (a 'packaging error'). Any gene from the bacterial chromosome can theoretically be transferred.
Specialized transduction occurs with temperate phages that integrate into the bacterial chromosome (lysogeny) at a specific site. When the phage genome excises imprecisely during induction into the lytic cycle, it can carry adjacent bacterial genes along with it, packaging only genes near the integration site.
Clinical significance: Transduction is responsible for the spread of important virulence factors and toxins in medically relevant bacteria. Classic USMLE examples include: - Corynebacterium diphtheriae: diphtheria toxin (tox gene) is phage-encoded - Clostridium botulinum: botulinum toxin - Streptococcus pyogenes: erythrogenic toxin (scarlet fever) and some strains carry phage-encoded superantigens - Shiga toxin in E. coli O157:H7 (Shiga-like toxin) is phage-encoded - Staphylococcal enterotoxins and Panton-Valentine leukocidin can be phage-mediated
This differs from other horizontal gene transfer mechanisms tested on boards: transformation (uptake of free DNA from environment), conjugation (direct cell-to-cell transfer via pilus, often plasmid-mediated, responsible for spreading antibiotic resistance genes), and transposition (jumping genes within/between DNA molecules).
Understanding transduction helps explain why certain toxigenic bacterial strains are pathogenic while genetically similar strains are not - the presence of a lysogenic phage carrying the toxin gene makes the difference.
Sources
- First Aid for the USMLE Step 1
- Sherris Medical Microbiology
- Murray's Medical Microbiology
- Kaplan USMLE Step 1 Microbiology Lecture Notes
Reviewed by AnkiBoss editorial — medical student review. Information here is for study reference only and is not medical advice. Spotted an error? Let us know.