PRESENCE OF ADDITIONAL PEPTIDASES IN STREPTOCOCCUS-THERMOPHILUS CNRZ-302 COMPARED TO LACTOCOCCUS-LACTIS

Streptococcus thermophilus is widely used in the dairy industry but li ttle is known about its peptidase system. The aim of this study was to determine the biochemical and genetic characteristics of this system, and to compare it to the well known system of Lactococcus lactis. We separated the intracellular proteins of Strep. thermophilus CNRZ 302 a nd L. lactis NCDO 763 by ion-exchange chromatography and we detected t he activity of the different types of peptidases. In both L. lactis an d Strep. thermophilus strains, we showed 13 different peptidase activi ties with biochemical homologies between both species. Streptococcus t hermophilus also possessed two peptidases which we did not find in L. lactis: an aminopeptidase and an oligopeptidase. We performed Southern blot experiments and among the eight peptidase genes tested, only the genes encoding the general aminopeptidases, pepC and pepN, were homol ogous between the L. lactis and Strep. thermophilus strains. Besides b iochemical and genetic similarities, the peptidase systems of Strep. t hermophilus and L. lactis thus differed by the presence of additional peptidases in Strep. thermophilus.