AUTOLYSIS OF LACTOCOCCUS-LACTIS CAUSED BY INDUCED OVERPRODUCTION OF ITS MAJOR AUTOLYSIN, ACMA

The optical density of a culture of Lactococcus lactis MG1363 was redu ced more than 60% during prolonged stationary phase, Reduction in opti cal density (autolysis) was almost absent in a culture of an isogenic mutant containing a deletion in the major autolysin gene, acmA. An acm A mutant carrying multiple copies of a plasmid encoding AcmA lysed to a greater extent than the wild-type strain did. Intercellular action o f AcmA was shown by mixing end-exponential-phase cultures of an acmA d eletion mutant and a tripeptidase (pepT) deletion mutant, PepT, produc ed by the acmA mutant, was detected in the supernatant of the mixed cu lture, but no PepT was present in the culture supernatant of the acmA mutant, A plasmid was constructed in which acmA, lacking its own promo ter, was placed downstream of the inducible promoter/operator region o f the temperate lactococcal bacteriophage rlt, After mitomycin inducti on of an exponential-phase culture of L. lactis LL302 carrying this pl asmid, the cells became subject to autolysis, resulting in the release of intracellular proteins.