Autolysis in Strains of Viridans Streptococci

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Abstract
Seven strains of viridans streptococci of the species Streptococcus sanguis, S. mutans and S. mitis were investigated for autolysis. The effect of pH, salt concentration and temperature on the autolytic process was studied in Na2HPO4/NaH2PO4 buffer. Whole cells and walls of all strains autolyzed most rapidly at pH values > 7. Autolysis of whole cells of S. sanguis and 1 strain of S. mitis (ATCC15909) was maximal in 0.05-0.2 M buffer, while the 2 S. mutans strains and S. mitis ATCC15912 showed maximal autolysis in 0.5 and 1.0 M buffers. Cultures harvested in the stationary phase of growth possessed only slightly decreased autolytic activity compared with those from the exponential phase. Whole cells autolyzed more rapidly at 37.degree. C than at 45.degree. C and 10.degree. C. Autolysis of isolated walls of 3 strains of S. mitis (ATCC903, ATCC15909 and ATCC15912) was maximal at pH 7.0 and 7.5 and in 1.0 M buffers. S. mitis ATCC15909 also showed maximal lysis in 0.01 M and 0.5 M buffers. An endopeptidase action of the autolytic system of S. mitis ATCC15912 was indicated by the progressive release of soluble amino groups during autolysis of the walls. No release of reducing groups was observed. Several free amino acids were released during autolysis of these walls, alanine, lysine and glutamic acid being in greatest quantity.