Cytotoxin-converting phages, phi CTX and PS21, are R pyocin-related phages

phi CTX is a temperate phage of Pseudomonas aeruginosa harbouring the ctx gene that encodes cytotoxin (CTX). We identified phi CTX as an R pyocin-related phage, by serological and molecular analysis, based on the findings that the infectivity of the phage was inhibited with the antisera directed R pyocins and R pyocin-related phages and that the phi CTX genome showed DNA homology to the genome of PS17 (a representative of the R pyocin-related phages) as well as to the pyocin R2 genes. Another new CTX-converting, R pyocin-related phage named PS21 was isolated from a CTX-producing strain of P. aeruginosa, suggesting the distribution of the ctx gene by certain members of R pyocin-related phage family.