Composition and molecular weight of pili purified from Pseudomonas aeruginosa K

Abstract

P. aeruginosa strain K (PAK) bears polar pili that promote infection by at least 6 bacteriophages. A recently isolated mutant of strain K (PAK/2PfS) is many times more piliated than the wild-type strain and facilitates the preparation of large amounts of pure pili for biochemical studies. The structural relatedness of PAK and PAK/2PfS pili was studied, and their biochemical composition was determined. A purification procedure is described for PAK and PAK/2PfS pili that yields about 8 mg of pure pili/100 g (wet wt) of PAK/2PfS cells and 0.8 mg of pure pili/100 g (wet wt) of PAK cells. PAK and PAK/2PfS pili were free from phosphate, carbohydrate and lipid and contained a single polypeptide subunit of 17,800 daltons. Isopycnic centrifugation studies revealed that PAK and PAK/2PfS pili have the same buoyant density in sucrose (1.221) and CsCl (1.295). Both types of pili banded at pH 3.9 when subjected to isoelectric focusing. Amino acid analyses showed that PAK and PAK/2PfS pili have identical amino acid compositions, and microimmunodiffusion studies revealed that the 2 types of pili are immunologically indistinguishable. PAK and PAK/2PfS pili are apparently identical. The mutation responsible for producing the multipiliated state in PAK/2PfS is probably located outside the structural gene for PAK pili.