Environmental regulation of glycosidase and peptidase production by Streptococcus gordonii FSS2

The synthesis of cell-associated and secreted proteins by Streptococcus gor donii FSS2, an infective endocarditis (IE) isolate, was influenced by both environmental ph and carbon source. Controlling the pH at 7.5 in stirred ba tch cultures showed that cell-associated and secreted protein concentration s were increased during late exponential and stationary phase by 68% and 12 5%, respectively, compared with similar cultures without pH control. The ex pression of five glycosidase and eight peptidase activities were examined u sing fluorogen-labelled synthetic substrates. Enzyme activities were signif icantly down-regulated during exponential growth, increasing during station ary phase (P < 0.01) whether the culture ph was controlled at ph 7.5 or all owed to fall naturally to pH 4.4. Culture-supernatant activities were signi ficantly increased (P < 0.05) when the ph was maintained at 6.0 or 7.5, ind icating modulation of enzyme activity by ph. Growth under nitrogen-limitati on/glucose-excess conditions resulted in a significant repression of cell-a ssociated glycosidase activities (P < 0.01), whilst in the supernatant, act ivities were generally reduced. The expression of peptidase activities in t he culture supernatant did not significantly change. The results suggest a possible role for catabolite repression by glucose in regulating enzyme exp ression. When S. gordonii FSS2 was cultured with 50% (v/v) added heat-inact ivated foetal bovine serum, several cell-associated enzyme activities incre ased initially but were then reduced as the culture time was extended to 11 6 h, Culture-supernatant enzyme activities (N-acetyl-beta-D-glucosaminidase , N-acetyl-beta-D-galactosaminidase, thrombin, Hageman factor, collagenase and chymotrypsin), however, were significantly increased (P < 0.01) over th e same time period. The findings indicated that most of the important glyco sidases synthesized by S. gordonii FSS2 were down-regulated by acid growth conditions and may also be subject to catabolite repression by glucose but conversely may be upregulated by growth in serum. These results may have im plications for streptococcal growth in an IE vegetation and in the mouth be tween meals or during sleep.