conjugative

Conjugative refers to genetic elements and processes that enable transfer of genetic material between bacterial cells by conjugation. Conjugative elements include conjugative plasmids, conjugative transposons, and integrative and conjugative elements (ICEs). These elements encode a set of genes, often referred to as the tra operon, that assemble a mating-pair formation apparatus and a DNA transfer machinery, enabling intercellular DNA transfer.

Mechanism typically begins when donor and recipient cells form a stable mating pair via a pilus or a Type IV secretion system. A relaxase enzyme introduces a site-specific nick at the origin of transfer (oriT) and remains covalently attached to the 5' end of the transfer strand. The DNA is unwound and transferred as a single strand through the transfer channel into the recipient, where it is converted to double-stranded DNA. The donor may retain a copy of the element, and the recipient can become a donor in subsequent transfers.

Conjugative plasmids often carry accessory traits such as antibiotic resistance, virulence factors, or metabolic capabilities, which can spread through populations. Some DNA elements are mobilizable but lack self-transfer genes and require a helper conjugative element; others are non-conjugative and rely on other elements for transfer.

Ecology and significance: Conjugation is a major mechanism of horizontal gene transfer in bacteria and contributes to genetic diversity and the spread of antibiotic resistance genes, especially in clinical and environmental settings. It is also observed in certain archaea and, to a lesser extent, in some Gram-positive bacteria.

Examples include the F plasmid in Escherichia coli, broad-host-range plasmids like RK2, and various integrative and conjugative elements such as SXT in Vibrio cholerae.