Prophage Curing in Lactobacillus casei by Isolation of a Thermoinducible Mutant

To eliminate the occurrence of virulent phage in industrial fermentation, attempts were made to obtain prophage-cured derivatives from Lactobacillus casei lysogenic strain S-1. A thermoinducible mutant lysogen was isolated from mutagenized strain S-1, since S-1 cannot be induced under laboratory conditions. The mutation responsible for thermoinducibility was located on the prophage. Prophage-cured strains were selected after heat induction of the mutant. These cured strains did not produce the virulent phage and should be valuable for industrial fermentation.