Identification of the lipopolysaccharide core region as the receptor site for a cytotoxin-converting phage, φCTX, of Pseudomonas aeruginosa

A temperate phage, φCTX, is a cytotoxin-converting phage of Pseudomonas aeruginosa. In this study, we characterized the lipopolysaccharide (LPS) structures of φCTX-resistant mutants derived from φCTX-sensitive strains. φCTX infectivity was neutralized by LPS preparations derived from sensitive strains but not by those from resistant strains. φCTX-resistant mutants had lower-molecular-weight rough (R)-type LPS than the parental strains and lacked the reactivity of some anti-LPS core monoclonal antibodies. Some LPS core components were lacking or significantly decreased in the resistant mutants. These results suggested that a receptor site of the cytotoxin- converting phage φCTX was the LPS core region and that especially L-rhamnose and D-glucose residues in the outer core were involved in phage binding. The host range of φCTX was nearly O-serotype dependent, probably because of the diversity of the LPS core structure among P. aeruginosa strains. φCTX bound to most strains of Homma serotypes A, G, and I but not to strains of serotypes B and E. Furthermore, we found that a genetic locus specifying φCTX sensitivity (and consequently participating in the biosynthesis of part of the LPS core) existed in or near the locus participating in the determination of O-serotype specificity (somA), which has been mapped between leu-10 and eda-9001. φCTX, as well as anti-LPS core monoclonal antibodies, will be a good tool for structural characterization of the P. aeruginosa LPS core region.