COMPARISON OF CELL-SURFACE PROTEINASE ACTIVITIES WITHIN THE LACTOBACILLUS GENUS

Whole cells of Lactobacillus delbrueckii subsp. bulgaricus CNRZ 397 (L b. bulgaricus CNRZ 397) are able to hydrolyse alpha- and beta-caseins. We have isolated a mutant of Lb. bulgaricus altered for growth in mil k and unable to hydrolyse alpha- or beta-casein. Normal growth was res tored by adding amino acids or tryptone to milk. No significant differ ence between the peptidase activities of parent and mutant strains was observed. The cell surface caseinolytic activities of three lactobaci lli species and Lactococcus lactis subsp. lactis (Lc. lactis) were com pared. As expected, the characteristics of the cell surface proteinase activity of Lb. casei were similar to those of Lc. lactis. We showed that the cleavage specificities of the cell surface proteinase activit ies from lactobacilli were species-dependent and at least three types of activity were distinguished. The regulation of the biosynthesis of cell surface proteinase activities was medium-dependent and different within the Lactobacillus genus and even within the Lb. delbrueckii spe cies. In contrast to Lb. bulgaricus, the cell surface Proteinase activ ity of Lb. lactis was totally inhibited in a medium rich in peptides o r amino acids. In contrast, the cell surface of Lb. helveticus probabl y displayed two proteinases with different cleavage specificities and with a biosynthesis regulation sensitive to different medium component s.