Protease and Peptidase Activity of Micrococcus Species

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Abstract
Nine different strains or species of micrococci were examined for intracellular protease and peptidase activity. Highest activities of leucine, alanine, and methionine aminopeptidases and proline iminopeptidase were found in Micrococcus sp. ATCC 398. Lysine aminopeptidase and dipeptidase activities were maximum in Micrococcus freudenreichii ATCC 407. Highest intracellular protease activity appeared in Micrococcus sp. LL3 isolated from Cheddar cheese. All strains except Micrococcus sp. ATCC 398 preferentially hydrolyzed the .beta.-casein component during growth in skim milk at 30.degree. C, and after longer incubation whole casein (.alpha.s1 and .beta.) was completely hydrolyzed. Micrococcus sp. ATCC 398 failed to grow in skim milk under our experimental conditions. This pattern of proteolysis also was observed when skim milk was incubated with cell-free extracts of all micrococci tested as well as during growth of Micrococcus caseolyticus ATCC 13548 in ultrafiltered milk (five-fold concentration).