Occurrence and distribution of sucrose-metabolizing enzymes in oral streptococci

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Abstract
Specific growth rates, growth yields and the level and cellular distribution of 3 sucrose-metabolizing enzyme activities were determined for 7 oral streptococci (Streptococcus mutans strains E49, BHT, 10449, SL-1 and LM-7, S. sanguis 10558 and S. salivarius 25975). Cultures were grown in a fermentor at pH 6 with 20 mM glucose or 10 mM sucrose. Generation times varied between 21-70 min. Whereas some strains grew 10-50% more slowly with sucrose than with glucose, others did not. Growth was always logarithmic and the growth yields were similar. Glucosyl transferase (EC 2.4.1.5) was largely extracellular; in sucrose cultures it was appreciably lower, but no major shift to a cell-associated form was found. In glucose cultures, the activity varied between 4-140 IU/6 l culture. The glucan formed was mostly or exclusively water insoluble. Glucosyl transferase was stimulated weakly (.ltoreq. 60%) by various dextrans. Fructosyl transferase (EC 2.4.1.10) was primarily extracellular (except in glucose cultures of S. salivariusj and varied between 0-337 IU/culture. In S. salivarius, the extracellular fructosyl transferase was induced by sucrose. In all S. mutans cultures, the total fructosyl transferase activity was lower after growth with sucrose. All strains had extra- and intracellular invertase (EC 3.2.1.26) activity. Total levels varied between 210-3500 IU/culture. Less extracellular activity was present in sucrose cultures. Only S. salivarius had appreciable activity in the cellular particulate fraction. Invertase activity was significantly higher than the combined glucosyl and fructosyl transferase activities in all cultures.