Functions of F Pili in Mating-Pair Formation and Male Bacteriophage Infection Studied by Blending Spectra and Reappearance Kinetics

The extent of removal at various blending speeds (blending spectrum) and the kinetics of reappearance after blending of the ability of male Escherichia coli bacteria to form mating pairs, to adsorb and be infected by ribonucleic acid male phage, and to adsorb and be infected by deoxyribonucleic male phage were identical to the blending spectrum and reappearance kinetics of microscopically visible F pili. The same results were obtained with an Hfr (high-frequency recombinant), F′, or resistance transfer factor (RTF) fi + mating system. Blending did not affect the viability, growth rate, ability to adsorb T4 phage, or ability to produce new F pili at any of the speeds used. It can be concluded that microscopically visible F pili are an absolute requirement for all three functions. Three classes of F pili have been found in bacterial cultures: attached, adsorbed, and free. Bacteria with adsorbed F pili in addition to attached ones were proportionately more susceptible to male phage infection, suggesting that adsorbed F pili may be at least partially functional. Free F pili did not compete with bacteria for phage. Some implications of the virus-like nature of F-pilus outgrowth for the mechanisms of mating and male phage infection are discussed.