Paper I
Question
Transduction
Answer
Transduction is a mechanism of horizontal gene transfer in which bacterial DNA is transferred from one bacterium (donor) to another (recipient) via a bacteriophage (bacterial virus) acting as the vector.
Types:
- Generalized transduction: occurs during the lytic cycle of a virulent (or lytic) phage. During assembly of new phage particles, the phage packaging machinery occasionally makes an error and packages a random fragment of the host bacterial chromosome (instead of, or along with, phage DNA) into a phage head. When this defective phage particle subsequently infects a new (recipient) bacterium, it injects the packaged bacterial DNA rather than phage DNA, which can then recombine into the recipient’s chromosome — any bacterial gene can potentially be transferred this way, hence “generalized.”
- Specialized (restricted) transduction: occurs with temperate (lysogenic) phages, which integrate their DNA into a specific site on the host chromosome (as a prophage) during lysogeny. On induction (excision from the chromosome to re-enter the lytic cycle), imprecise excision can occasionally carry adjacent bacterial genes (specifically those flanking the phage integration site) along with the phage genome into the new phage particle — so only genes near the specific prophage attachment site can be transferred, hence “specialized.”
Clinical/biological significance: transduction can transfer genes for toxin production (e.g., diphtheria toxin in toxigenic Corynebacterium diphtheriae, erythrogenic/pyrogenic toxin in Streptococcus pyogenes, Shiga-like toxin in some E. coli strains — all examples of lysogenic/phage conversion, where a prophage itself carries the toxin gene) as well as antibiotic resistance genes, contributing to bacterial pathogenicity and the spread of drug resistance.