Effect of mucin and glucose on proteolytic and glycosidic activities of Streptococcus oralis

Abstract

The production of glycosidase and protease activities, which may play a role in the degradation of human glycoproteins, by Streptococcus oralis strains isolated from endocarditis, septicaemia or the oral cavity was investigated with a range of fluorogenic substrates. The pH optima of the proteases ranged from 6.0 to 9.3 and the pH optima for the glycosidases were lower (4.5-6.0), although the pH range over which both groups of enzymes acted was broad. Growth in a minimal medium supplemented with glucose resulted in repression of glycosidase activities and elevated proteolytic activity. Bacteria from cultures supplemented with porcine gastric mucin (PGM), a model glycoprotein, exhibited higher levels of glycosidase activity, while proteolytic activity was suppressed and glycoprotein-derived monosaccharides were transported at significantly higher rates than those observed for cells grown in media with glucose. PGM-derived cells also exhibited high levels of N-acetylneuraminate pyruvate-lyase, the first intracellular enzyme in the pathway of sialic acid catabolism. Taken together, these data indicate that S. oralis strains produce a range of proteolytic and glycosidic enzymes that may play a role in the degradation of host-derived glycoproteins.