Sex pili and common pili in the conjugational transfer of colicin factor Ib by Salmonella typhimurium

Abstract

The kinetics of spread of colicin factor Ib (colIb) in col− cultures of S. typhimurium was studied. The rate of spread was greater with pil+ strains (those forming common pili) than with pil− strains. The difference reflects inefficient pairing between pil− cells, which donate or receive colIb efficiently only when mated with pil+ cells. The donor function of colIb is known to be repressed a few generations after it is acquired by a col− cell. While donor ability is manifest, a new type of pilus (the ‘Ib pilus’) is formed which is morphologically distinct from common pili and other sex pili such as that determined by the F factor. The Ib pilus is presumably involved in the transfer of colIb by conjugation.