Modulation of glycosidase and protease activities by chemostat growth conditions in an endocarditis strain of Streptococcus sanguis

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Abstract
The effects of growth conditions on the properties of the endocarditis‐producing oral bacterium Streptococcus sanguis FSS2 were studied. This strain produces a variety of proteases and glycosidases, including a thrombin‐like activity that is a potential virulence factor for endocarditis. Cultures were grown with limiting glucose or galactose in chemostats over a range of dilution rates and pH levels, and the following activities were measured at pH 7.5: thrombin‐like, Hageman factor‐like, N‐acetyl‐β‐D‐galactosaminidase, β‐D‐glucosidase, and β‐D‐galactosid‐ase. At growth pH 6.5, specific activities generally decreased as the dilution rate increased from 0.05 to 0.40 h−1. At a dilution rate of 0.1 h−1 specific activities generally were highest at growth 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 specific 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 conditions and thus were modulated by environment. Environmental regulation of thrombin‐like activity by pH is consistent with an activity that is less important on tooth surfaces than in tissues.