F and type 1 piliation of Escherichia coli

F and type 1 piliation of various Escherichia coli K12 Hfr and F+ strains was re-examined by using a new visualization assay. In anaerobic cultures in rich media, bacteria were well F piliated throughout all growth phases. In aerobic cultures in rich media, F piliation reached a maximum in the mid-exponential phase. The yield of pili was up to 15 mg 1(-1). In aerated cultures, F pili disappeared in the late exponential phase. In rich media F pili were on average 10-20 micron long; in synthetic media they were an order of magnitude shorter, and less numerous. Addition of metabolic poisons (NaCN, NaN3, Na3AsO4, phenylethyl alcohol) and starving the bacteria caused rapid disappearance of F pili under aerobic conditions, but had no influence on F piliation under anaerobic conditions. Type 1 piliation was not influenced by these drugs or by an alteration of growth conditions.