The Diversity of Potential Cheese Ripening Characteristics of Lactic Acid Starter Bacteria: 1. Resistance to Cell Lysis and Levels and Cellular Distribution of Proteinase Activities

By reference to subcellular fraction markers, the resistance to lysis of 23 strains of Lactococcus lactis subsp, cremoris, 30 strains of L. lactis subsp. lactis and five strains of Streptococcus thermophilus and the levels and distribution of proteinase activity in the strains were determined. Strains of L. lactis subsp, cremoris were readily lysed by transfer to hypotonic buffer after treatment with lysozyme alone, whilst strains of L. lactis subsp, lactis and S. thermophilus could be efficiently; lysed in this way only after treatment with a combination of lysozyme and mutanolysin. With a. few notable exceptions, those strains which gave the. fastest rates of acid production also generally presented higher levels of cell surface proteinase, as determined by activity on.fluorescein isothioeyanate-labelled beta-casein. The highest levels of cell surface proteinase detected were found for strains of L. lactis subsp, cremoris. However, the levels of total proteinase activity, in the lactococcal strains did not correlate with the rate of acid production in milk, some slow acid-producers yielding similar or greater total proteinase levels than. fast acid-producers. Homology to DNA probes or the lactococcal cell surface proteinase gene and to the conserved region encoding the serhw proteinase active site was shown by the. fast acid-producing lactococcal strains, but not by most of the slow acid-producing lactococcal strains or by, the strains of S. thermophilus. A significant proportion of the total proteinase activity was recovered in the subcellular fraetions in which high levels of cytoplasmic marker enzyme activity were found. The total proteinase levels detected in strains of L. lactis subsp, lactis showed a greater range variation lhatl in tile Strains of L. lactis subsp, cremoris. High levels of total proteinase activity were. found ill the slow acid-producers despite tile strains having been growth in the presence of'yeast extract. For many of the straills, the levels of proteinase released from the cell, Surface during cell wall degradation with lytic enzyme treatment were higher than lose found using whole cells, suggesting that a significant amount of proteolytic activity was either inaccessible to substrate or present in an inactive form.