Multilevel control of extracellular sucrose metabolism in Streptococcus salivarius by sucrose.

Standardized experimental conditions were established to test the role of sucrose in the regulation of control of its metabolism in Streptococcus salivarius. A fresh isolate of S. salivarius was used. The extracellular dextranase activity of cells grown on sucrose was 10-fold higher than that of cells grown on glucose, fructose or galactose. This activity increased in less than 5 min following the addition of sucrose to galactose-grown cells, a phenomenon which was affected by neither rifampicin nor chloramphenicol which inhibit transcription and translation, respectively. Extracellular fructanase activity was 2-fold higher when cells were grown on sucrose than when they were grown on the other sugars. This increase also occurred within 5 min, but was diminished by transcriptional and translational inhibitors. De novo synthesis was required for the production of extracellular glucosyltransferase (GTF) activity which, upon the addition of sucrose, became associated with the cell surface. Conversely, cell-associated fructosyltransferase (FTF) activity appeared to require genetic induction for its production and cell-surface association, but required sucrose for its release from the surface framework. Versatility in the control mechanisms of this complex set of enzymes allows their expression and function to be regulated at several widely separated stages in the life histories of these proteins.