Screening for differences in the proteolytic systems of Lactococcus, Lactobacillus and Propionibacterium

The caseinolytic, and the endo- and aminopeptidase activities of the intracellular (IC) and cell-envelope-associated (CE) fractions of selected strains of Lactococcus, Lactobacillus and Propionibacterium have been compared. With the exception of one Lactococcus strain, most of the caseinolytic activity of the three genera was located in the IC fraction, as was the case for the amino- and endopeptidases. The lactococci showed low activity on Pro-pNA and high activity on Gly-Pro-pNA, the reverse was characteristic for the propionibacteria (PAB) while lactobacilli took an intermediary position. Lactococcus lactis ssp. cremoris INF-C12 was the strain with the highest total endopeptidase activity. The experiment with phosphoramidon and a peptide inhibitor, β-casein f58–72 (β-CN f58–72), indicated differences of IC endopeptidases of lactic acid bacteria (LAB) and PAB. In contrast to the LAB endopeptidases, the PAB endopeptidases were little inhibited by β-CN f58–72, and were not affected by phosphoramidon. Lysozyme was used to produce spheroplasts from whole cells; however, the susceptibility to such treatment varied. Intracellular material, ≥97%, was easily released from the lactococci strains, for other strains additional sonication was most often necessary for ≥93% lactate dehydrogenase release.