Regulation of Pilus Expression
122The expression of Escherichia coli somatic pili is a regulated process. The pilus K99 was used as a prototype to study quantitative variation of pilus expression. The appearance of K99 on the extracellular surface of E. coli occurs only during the logarithmic phase of growth. However, net subunit synthesis occurs throughout the life cycle of the bacterial culture including the times when extracellular cell-bound K99 is not being produced. In minimal medium, glucose does not affect the appearance of K99 on the cell surface, contrary to the effect observed in a rich medium, yet net subunit synthesis is decreased by glucose. Expression of K99 on the cell surface is unaffected by chloramphenicol while subunit synthesis is totally inhibited. These results are consistent with the hypothesis that pilus outgrowth (appearance on the cell surface) and subunit synthesis are two different processes and are possibly controlled independently. Production of K99 by cells grown at 18°C is completely inhibited.