Comparative study on R-type pyocins of Pseudomonas aeruginosa

Four R-type pyocins (R1, R2, R3, and R4) produced by different Pseudomonas aeruginosa strains were compared with respect to their structure and action methanism. It is known that these bacteriocins have structures similar to contractile bacteriophage tails and serologically cross-react with each other, but they are distinguished according to difference in range of sensitive strains. All these pyocins were shown to arrest the synthesis of protein and nucleic acid in sensitive cells, as previously reported for pyocin R1. Action of pyocin R3 was shown to require calcium ion. Although antiserum prepared against one pyocin neutralized other R-type pyocins as well as the homologous pyocin, some differences in antigen specificity were found between pyocin R1 and pyocin R2 and R3 antibody blocking assays. Electron microscopic observation of pyocin particles treated with the antiserum pre-absorbed with heterologous pyocin revealed that specific antigens were located on the distal portion of the fibers. Comparison of protein composition showed these pyocins to be composed of essentially similar subunit proteins but a subunit protein supposed to be a main constituent of the fiber was different in its molecular weight among these pyocins. These results suggest that the main structural difference of these pyocins is to be found in the fiber.