Question
Mention two methods of extra chromosomal transfer of genetic material in bacteria
Answer
Two methods of extrachromosomal transfer of genetic material (horizontal gene transfer) in bacteria:
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Conjugation — direct cell-to-cell transfer of plasmid DNA (e.g., the F plasmid or an R plasmid) from a donor to a recipient bacterium through a specialized surface appendage, the sex pilus (F pilus), which draws the two cells together to form a conjugation bridge through which single-stranded plasmid DNA passes and is then replicated to double-stranded form in the recipient. This is the principal mechanism by which R plasmids carrying multiple antibiotic-resistance genes spread rapidly between bacteria, even across different genera.
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Transduction — transfer of bacterial DNA from one bacterium to another via a bacteriophage acting as the vector. In generalized transduction, a lytic phage occasionally packages a random fragment of host bacterial DNA instead of phage DNA during virion assembly, transferring it to the next bacterium it infects. In specialized transduction, a temperate phage integrated at a specific chromosomal site can, on induction, carry adjacent bacterial genes along with its own genome into new phage particles.
(A third mechanism, transformation — uptake of free/naked DNA from the environment by a competent bacterial cell — is also sometimes included among horizontal gene transfer mechanisms, though it does not always involve extrachromosomal/plasmid DNA specifically.)