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 p yocin-related phage, by serological and molecular analysis, based on t he findings that the infectivity of the phage was inhibited with the a ntisera directed R pyocins and R pyocin-related phages and that the ph i CTX genome showed DNA homology to the genome of PS17 (a representati ve 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 isol ated from a CTX-producing strain of P. aeruginosa, suggesting the dist ribution of the ctx gene by certain members of R pyocin-related phage family.