MODULATION OF GLYCOSIDASE AND PROTEASE ACTIVITIES BY CHEMOSTAT GROWTH-CONDITIONS IN AN ENDOCARDITIS STRAIN OF STREPTOCOCCUS-SANGUIS

The effects of growth conditions on the properties of the endocarditis -producing oral bacterium Streptococcus sanguis FSS2 were studied. Thi s strain produces a variety of proteases and glycosidases, including a thrombin-like activity that is a potential virulence factor for endoc arditis. Cultures were grown with limiting glucose or galactose in che mostats over a range of dilution rates and pH levels, and the followin g activities were measured at pH 7.5: thrombin-like, Hageman factor-li ke, N-acetyl-beta-D-galactosaminidase, beta-D-glucosidase, and beta-D- galactosidase. At growth pH 6.5, specific activities generally decreas ed as the dilution rate increased from 0.05 to 0.40 h(-1). At a diluti on rate of 0.1 h(-1), specific activities generally were highest at gr owth pH 6.5 and lower and approximately equal at growth pH 5.5 and 7.5 . The major exception was the thrombin-like activity, for which the sp ecific activity at growth pH 7.5 was approximately 5-fold higher than at growth pH 5.5. Hageman factor-like activity was apparently glucose catabolite repressible, as its activity was 3-fold higher in galactose cultures. The measured activities changed as functions of growth cond itions and thus were modulated by environment. Environmental regulatio n of thrombin-like activity by pH is consistent with an activity that is less important on tooth surfaces than in tissues.