Conjugation

For conjugation in grammar, see Verb.

Conjugation is a temporary union of two organisms, usually bacteria, for the purpose of DNA transfer. It is one of the three major ways in which genes can be transferred between different species (horizontal gene transfer), the others being transformation and transduction. Horizontal gene transfer is a major cause of antibiotic resistance; if a pathogenic bacterium picks up resistance genes by chance, and then is exposed to antibiotics, this causes natural selection and ensures that the resistant cells survive and multiply.

Conjugation between two cells of the same bacterial species involves a thin tube joining the cells and transferring DNA, but when two different species are involved the bacteria form a larger structure called a protoplast, where the cell walls form the bridge between the cells.