The pyocins of Pseudomonas aeruginosa

Pyocins are produced by more than 90% of Pseudomonas aeruginosa strains and each strain may synthesise several pyocins. The pyocin genes are located on the R aeruginosa chromosome and their activities are inducible by mutagenic agents such as mitomycin C. Three types of pyocins are described. (i) R-type pyocins resemble non-flexible and contractile tails of bacteriophages. They provoke a depolarisation of the cytoplasmic membrane in relation with pore formation. (ii) F-type pyocins also resemble phage tails, but with a flexible and non-contractile rod-like structure. (iii) S-type pyocins are colicin-like, protease-sensitive proteins. They are constituted of two components. The large component carries the killing activity (DNase activity for pyocins S1, S2, S3, AP41; tRNase for pyocin S4; channel-forming activity for pyocin S5). It interacts with the small component (immunity protein). The synthesis of pyocins starts when a mutagen increases the expression of the recA gene and activates the RecA protein, which cleaves the repressor PrtR, liberating the expression of the protein activator gene prtN. R and F-pyocins are derived from an ancestral gene, with similarities to the P2 phage family and the lambda phage family, respectively. The killing domains of S 1, S2, AP41 pyocins show a close evolutionary relationship with E2 group colicins, S4 pyocin with colicin E5, and S5 pyocin with colicins Ia, and Ib. (C) 2002 Societe francaise de biochimie et biologic moleculaire / Editions scientifiques et medicales Elsevier SAS. All rights reserved.