Transduction is the transfer of genetic material from one bacterium to another via a bacteriophage, a virus that infects bacteria. This process allows DNA to move between cells without direct contact or environmental uptake.
Explanation
In generalized transduction, bacteriophages in the lytic cycle accidentally package fragments of host DNA instead of their own genome. When these defective virions infect another bacterium, they inject the donor DNA, which may recombine with the recipient’s chromosome if homologous sequences are present. Specialized transduction occurs with temperate phages that integrate into a specific site on the bacterial chromosome during the lysogenic cycle. When they excise, they may mistakenly take adjacent bacterial genes with them, so only genes near the integration site are transferred. Transduction contributes to genetic diversity in microbial populations and can spread virulence factors or antibiotic resistance. The process was first described by Joshua Lederberg and Norton Zinder in 1952 using Salmonella. Transduction has been used as a tool in microbial genetics to map chromosomal locations by measuring the frequency of co-transduction, providing insights into gene linkage and organization. In nature, transduction is a significant means of horizontal gene transfer, influencing bacterial evolution by disseminating metabolic traits, toxin genes and resistance determinants.
Important Examples and Applications
One of the classic models is the P1 phage, which mediates generalized transduction in Escherichia coli; it can carry fragments of host DNA up to about 90 kilobases. The bacteriophage P22 performs a similar role in Salmonella species. Specialized transduction is well illustrated by the lambda phage of E. coli, which integrates into the attB site between the gal and bio operons. When imprecise excision occurs, it can carry gal or bio genes into new hosts, conferring new metabolic capabilities. In clinical contexts, transduction can spread toxin genes such as the Shiga toxin carried by lambdoid phages in E. coli O157:H7 or the gene encoding diphtheria toxin in Corynebacterium diphtheriae. Phage-mediated transfer of antibiotic resistance genes has been documented in Staphylococcus aureus, contributing to the emergence of methicillin-resistant strains. Researchers also harness transducing phages as vectors for genetic manipulation, enabling targeted delivery of genetic material into bacteria.
Transduction is a phage-mediated mechanism of gene transfer that shapes bacterial genomes. By moving genes among related bacteria, it plays an important role in evolution and in the spread of clinically relevant traits. Understanding transduction is essential in microbiology and biotechnology because it influences pathogenesis and provides tools for genetic analysis.
Related Terms: Conjugation, Transformation, Lysogeny, Bacteriophage, Horizontal gene transfer