Genetic complementation analysis of Escherichia coli type 1 somatic pilus mutants

A genetic complementation analysis of 75 stable nonpiliated mutants of a type 1 piliated strain of Escherichia coli K-12, AW405, was performed. Strains containing pairs of pil mutations were constructed by the infectious transfer of an F101 plasmid containing one pil mutation into E. coli K-12 AW 405 containing another pil mutation. The presence or absence of type 1 pili on the merodiploid strains was determined by agglutination with type 1 pilus antiserum. All 75 mutants fell into one of four complementation groups. The pattern of complementation defined three cistrons involved in pilus formation, pilA, pilB, and pilC. The fourth complementation group was composed of a large number of mutants defective in both pilA and pilB functions.