Amino acid requirements and proteolytic activity of Streptococcus sanguis.

The growth response of Streptococcus sanguis groups 1:A and 1:B in a complete chemically defined medium was not influenced by the oxygen concentration of the growth atmosphere. All of the cultures required cysteine and arginine; tyrosine and branched-chain amino acids were frequently required. Proteolysis of casein, mucin, and the anionic proteins of germfree rat saliva by S. sanguis was demonstrated. Hydrolytic activity toward casein was found in the soluble contents of the cells and in the cellular debris after disruption of the cells, with the soluble fractions exhibiting greater proteolytic activity toward casein. The soluble fractions from S. sanguis did not hydrolyze mucin, but this substrate was hydrolyzed by the cell debris fraction. When the amino acid requirements and proteolytic activity of S. sanguis and S. mutans were compared, these two oral streptococcal species exhibited distinct and characteristic differences.