Optimum Cultural Conditions for Induction of Temperate Bacteriophages in Lactic Streptococci

Nineteen strains of lactic-group streptococci were examined for lysogeny by treatment with ultraviolet light; eight were inducible. The effectiveness of lysogenic induction with ultraviolet light or mitomycin C depended on the dose of inducing agent, temperature of incubation, and age of the culture. Strain-specific differences in responses to all of these factors were observed; however, in general induction was most effective at temperatures of 30 C or less and when cultures were in mid-exponential growth. No single ultraviolet or mitomycin C dose would induce all eight strains. Cultures which had been frozen and thawed were generally not inducible immediately after thawing. This was attributed to inhibition of bacterial growth by freezing. Cultures which had been chilled without freezing remained inducible. Lysogenic induction was not affected by either calcium or phosphate.