Extracellular Peptidases in Group N Streptococci used as Cheese Starters

Strains of Streptococcus cremoris which utilized peptides had a mercaptoethanol‐sensitive, Mg 2+ ‐activated dipeptidase which could be released from the cells by lysozyme. A similar enzyme was inferred to be present in Strep. lactis. An apparently cell wall‐bound peptidase was only found in Strep. lactis ; this was also Mg 2+ ‐activated but was insensitive to mercaptoethanol. The peptidase recovered from culture‐supernatants of Strep. cremoris and Strep. lactis was similar to one of the two EDTA‐sensitive intracellular dipeptidases present in both organisms, but was distinct from the lysozyme‐released enzymes. The significance of these cell‐bound extracellular peptidases in relation to peptide utilization is discussed.