The F factor is often associated with Escherichia coli and appears to have been adapted by the bacterial host to act as an agent of genetic exchange and evolution. F encodes a type IV secretion system (T4SS) that enables bacterial conjugation, the transfer of DNA from a donor F+ to a recipient F− cell. The delivery of DNA containing either host or foreign genes has important consequences for the bacterium, allowing it to enlarge or modify its genetic content and rapidly adapt to an environmental niche. Unlike other plasmids, the conjugative functions of F and F-like plasmids appear to be controlled by a complex regulatory network that involves many host proteins resulting in a symbiotic relation between F and its host. This chapter outlines the predicted and known functions for all the genes on the F plasmid and its close relatives, and describes our current knowledge about the regulation of F conjugation.

BRIEF HISTORY OF THE F PLASMID

The discovery of horizontal gene transfer between bacteria can be attributed to the work of Lederberg and Tatum (1946), who observed that different strains of E. coli K-12 could be genetically and phenotypically altered when mixed together. A series of experiments led to the conclusion that direct contact between bacteria was required in order for genetic material to be transferred between the cells (Davis, 1950). This transfer was found to occur in one direction, from donor to recipient cells, by a mechanism contained within the donor cells (Hayes, 1952).