Phage‐conversion of cytotoxin production in Pseudomonas aeruginosa

We isolated a temperate phage which carried the cytotoxin gene (ctx) from a cytotoxin (CTX)‐producing Pseudomonas aeruginosa strain, PA158. The phage, φCTX, had a head with a hexagonal outline and a contractile tail with tail fibres. The phage genome was a linear double‐stranded 35.5kb DNA with single‐stranded cohesive ends (cos). The attP, cos and ctx genes were all located very close to one another within a 2.3kb segment on the phage genome in the order given (in the circular form). φCTX converted CTX non‐producing P. aeruginosa strains into CTX producers. A single copy of φCTX DNA was integrated at the same site on the host chromosome (attB) in every lysogen, including PA15B. However, the amount of CTX produced in these lysogens varied from strain to strain and was less than that in PA158.