Regulation of Dextransucrase Formation by Streptococcus sanguis

The dextransucrase formation by Streptococcus sanguis, strain 804, was studied under standardized and reproducible conditions in continuous culture. At state growth in complex medium the enzyme activity was high at low dilution rates and decreased when the dilution rate increased. At steady-state growth in chemically defined medium, the enzyme activity was very low at all dilution rates. In batch culture in complex medium the enzyme activity increased with a linear differential rate during the logarithmic phase of growth. In chemically defined medium in batch culture, the enzyme activity was hardly detectable. A significant increase in enzyme activity in the culture was demonstrated in the transitional stage between steady-state growth in the defined medium and in the complex medium. The enzyme activity in the culture during this transitional stage was more than 20 times higher than the activity at steady-state growth in the defined medium and two times higher than the activity at steady-state growth in the complex medium. There were no indications that the observed variation in enzyme activity in the culture could be ascribed to inhibitory or stimulatory substances. The variation in enzyme activity in the cultures may reflect differences in enzyme formation.The present results indicate that dextransucrase may only be formed in the mouth when there is an excess of nutrients available for the organism.