Summary: Strain 1, an avirulent non-slime-producing variant of 60, had greater bacteriocinogenic activity than did strain 60 both in liquid and on solid medium. The bacteriocin synthesized by strain 1 inhibited the growth of 43 of 51 strains tested. It had no effect on strain 1, strain 60, or selected strains from 10 other bacterial species. Although the optimal growth temperature for strain 1 was 32°C, the temperature most favourable for bacteriocin production was 30°C. Bacteriocin titre could be increased by short exposure to ultraviolet light but not by chemical inducing agents.

The bacteriocin produced by strain 1 was purified from the culture supernatant by ammonium sulphate precipitation, anion exchange chromatography, membrane ultrafiltration and preparative electrophoresis. Purified bacteriocin, being non-sedimentable, thermolabile and sensitive to proteolytic enzymes, resembled the S-type bacteriocins produced by aeruginosa. As determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis, the purified bacteriocin had a molecular weight of approximately 65000. It was insensitive to chloroform, nucleases and phospholipase. Although the bacteriocin present in culture supernatant was stable for 3 months at 4°C, the activity of purified bacteriocin declined rapidly under a variety of storage conditions. Maximum pH stability was between 6 and 8.


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