Presence of additional peptidases in Streptococcus thermophilus CNRZ 302 compared to Lactococcus lactis.

Streptococcus thermophilus is widely used in the dairy industry but little 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 and L. lactis NCDO 763 by ion-exchange chromatography and we detected the activity of the different types of peptidases. In both L. lactis and Strep. thermophilus strains, we showed 13 different peptidase activities with biochemical homologies between both species. Streptococcus thermophilus 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 homologous between the L. lactis and Strep. thermophilus strains. Besides biochemical and genetic similarities, the peptidase systems of Strep. thermophilus and L. lactis thus differed by the presence of additional peptidases in Strep. thermophilus.