Requirement of autolytic activity for bacteriocin-induced lysis

The bacteriocin produced by Lactococcus lactis IFPL105 is bactericidal agai nst several Lactococcus and Lactobacillus strains. Addition of the bacterio cin to exponential-growth-phase cells resulted in all cases in bacteriolysi s. The bacteriolytic response of the strains was not related to differences in sensitivity to the bacteriocin and was strongly reduced in the presence of autolysin inhibitors (Co2+ and sodium dodecyl sulfate). When L. lactis MG1363 and its derivative deficient in the production of the major autolysi n AcmA (MG1363acm.4 Delta 1) were incubated with the bacteriocin, the latte r did not lyse and no intracellular proteins were released into the medium. Incubation of cell wall fragments of L. lactis MG1363, or of L. lactis MG1 363acmA Delta I to which extracellular AcmA was added, in the presence or a bsence of the bacteriocin had no effect on the speed of cell wall degradati on. This result indicates that the bacteriocin does not degrade cell walls, nor does it directly activate the autolysin AcmA. The autolysin was also r esponsible for the observed lysis of L. lactis MG1363 cells during incubati on, with nisin or the mixture of lactococcins A, B, and M. The results pres ented here show that lysis of L. lactis after addition of the bacteriocins is caused by the resulting cell damage, which promotes uncontrolled degrada tion of the cell walls by AcmA.