Bacterial conjugation

Conjugation transfers genetic material between bacterial cells by a mechanism requiring cell-to-cell contact or close physical association. It is distinct from transformation, in which cells take up DNA from their surroundings, and transduction, in which bacterial viruses carry DNA between cells. Conjugation is a major route of horizontal gene transfer, the movement of genes other than from parent cell to offspring.

In a common form of conjugation, a donor carries a conjugative plasmid: a DNA molecule with genes that enable its transfer. Transfer machinery brings donor and recipient cells together, and DNA-processing proteins prepare a strand of plasmid DNA for passage into the recipient. Each cell synthesizes a complementary strand, so the donor typically retains a copy while the recipient may acquire the plasmid. The best-studied systems include the F factor of Escherichia coli, but mechanisms and transfer structures differ among bacterial groups; not all conjugation is mediated by the same kind of pilus or apparatus.

A transferred plasmid can introduce new genes into a recipient, but inheritance and expression depend on compatibility with the recipient and other biological conditions. Conjugative elements may carry genes involved in antibiotic resistance, metabolism or other traits, and can move among bacteria in settings such as microbial communities and biofilms. Transfer alone does not guarantee that a trait will persist: the DNA must be maintained and its effects shaped by selection and the recipient’s cellular context. Antibiotic exposure can favor resistant bacteria, while conjugation is one of several processes that can spread resistance genes.

In 1946, Joshua Lederberg and Edward Tatum reported genetic recombination in Escherichia coli. Their work challenged the view that bacteria lacked mechanisms for genetic exchange and opened a new field of bacterial genetics. Later research characterized conjugation as one route by which bacterial DNA can pass between cells; the historical experiment established recombination, rather than providing the full molecular account of modern conjugation mechanisms.