BIOCHEMICAL-STUDIES ON PILI ISOLATED FROM PSEUDOMONAS-AERUGINOSA STRAIN PAO

P. aeruginosa strains PAO and PAK bear polar pili which are flexible filaments having a diameter of 6 nm and an average length of 2500 nm. Both types of pili are retractile and promote infection by a number of bacteriophages. The partial biochemical characterization of PAO pili isolated from a multipiliated nonretractile mutant of PAO is described. The observed properties are compared to those of PAK pili which were characterized previously. PAO pili contain a single polypeptide subunit of 18,700 daltons. This is similar to PAK pili which contain a single polypeptide of 18,100 daltons. The amino acid composition of PAO pilin is also similar to that of PAK pilin. Neither protein contains phosphate or carbohydrate residues and both contain N-methylphenylalanine at the amino terminus. Sequencing of 20 amino acid residues at the amino terminal end of PAO pilin revealed the sequence to be identical with that of PAK pilin, while tryptic peptide analyses of PAO and PAK pilin indicated that the 2 proteins probably contain a number of homologous regions within the polypeptide. PAO and PAK pili are closely related structures.