The R-type pyocin of Pseudomonas aeruginosa is related to P2 phage, and the F-type is related to lambda phage

Pseudomonas aeruginosa produces three types of bacteriocins: R-, F- and S-t ype pyocins. The S-type pyocin is a colicin-like protein, whereas the R-typ e pyocin resembles a contractile but non-flexible tail structure of bacteri ophage, and the F-type a flexible but non-contractile one. As genetically r elated phages exist for each type, these pyocins have been thought to be va riations of defective phage. In the present study, the nucleotide sequence of R2 pyocin genes, along with those for F2 pyocin, which are located downs tream of the R2 gene cluster on the chromosome of P. aeruginosa PAO1, was a nalysed in order to elucidate the relationship between the pyocins and bact eriophages. The results clearly demonstrated that the R-type pyocin is deri ved from a common ancestral origin with P2 phage and the F-type from lambda phage. This notion was supported by identification of a lysis gene cassett e similar to those for bacteriophages. The gene organization of the R2 and F2 pyocin gene cluster, however, suggested that both pyocins are not simple defective phages, but are phage tails that have been evolutionarily specia lized as bacteriocins. A systematic polymerase chain reaction (PCR) analysi s of P. aeruginosa strains that produce various subtypes of R and F pyocins revealed that the genes for every subtype are located between trpE and trp G in the same or very similar gene organization as for R2 and F2 pyocins, b ut with alterations in genes that determine the receptor specificity.