Antibody-stimulated Increase in Sex Pili in R⁺ Enterobacteria

Abstract

ALTHOUGH a single bacterium may bear hundreds of common pili there are seldom more than two or three sex pili, corresponding roughly to the number of copies of the sex factor genome. This finding supports the suggestion that efficient transfer of F is due to the location of its genome near the mating substance on the cell surface¹, and fits with a more recent observation that transfer of a given sex factor only occurs in the presence of pili determined by its own genome². We report here a new observation, that the number of sex pili can be enormously increased simply by exposing metabolically active bacteria to antiserum to the sex pilus. These experiments show that there are fifty or more potential sites for pilus extrusion, not two or three as previously supposed.