Bacteriocinogeny in Proteus vulgaris

Abstract

One hundred and eighteen different strains of Proteus vulgaris were investigated for bacteriocinogeny. These P. vulgaris strains were also used a s indicators. Seventy of the 118 strains produced zones of inhibition when cross-streaked with the other P. vulgaris strains. Sixty-seven of the strains had a non-transmissible killing effect on one or more of the indicator organisms and subcultures of areas of inhibition to broth also failed to show growth. Thirty of the 67 bacteriocins with different spectra of activity were further investigated, Individual bacteriocins killed from five to 87 of the P. vulgaris indicators. Nine bacteriocins had similar host ranges whereas the host ranges of the remaining 58 bacteriocins differed. All these strains as well as the non-bacteriocinogenic Proteus strains displayed a Dienes demarcation line between their swarms. When tested against a number of gram-negative bacteria the bacteriocins only inhibited P. vulgaris and P> mlrabllls strains and had no effect on strains of the family Enterobacteriaceae. Broth cultures of bacteriocinogenic strains are inducible by ultraviolet light and yield bacteriocin titres of about 1/100. Activity can be concentrated with 40% ammonium sulphate and is sedimentable by high speed centrifugation„ The bacteriocins were electrophoretically immobile and diffused through agar. Activity could be destroyed after 20 min. at a temperature of 60 and also by the action of trypsin. Chemical analysis showed the bacteriociyis to consist of protein and to contain no DNA. Electron microscopy of all 30 preparations revealed similar phage tail-like structures with a contractile sheath round a hollow core. The particles resemble some pyocins and also the tail of a Proteus vulgaris transducing phage. In two preparations a few phage-like particles which resemble other Proteus phages were also seen. Bacteriocin activity was always associated with uncontrqcted sheaths and triggered tails do not adsorb to susceptible organisms. It is concluded that the tail-like structures are the products of defective lysogeny. The high incidence of defective lysogeny may be accounted for by the selection of genes which impart a selective advantage to the host and which were originally acquired through transduction or lysogenic conversion.