MECHANISM OF INHIBITION OF ACID PRODUCTION IN STREPTOCOCCUS-MUTANS BYSODIUM-IONS UNDER STRICTLY ANAEROBIC CONDITIONS

Acids excreted and intracellular levels of glycolytic intermediates du ring glucose metabolism in Streptococcus mutans NCTC 10449 under stric tly anaerobic conditions were quantified in an attempt to understand t he effect of sodium ions on bacterial acid production, In the presence of NaCl (0.15-0.30 M), the total amount of individual carboxylic acid s excreted was inhibited by up to 31%. The intracellular level of fruc tose 1,6-bisphosphate increased by 58% and levels of 3-phosphoglycerat e and pyruvate decreased by 46% and 12%, respectively. Sodium ions dir ectly inhibited the activities of fructose 1,6-phosphate aldolase and triose phosphate isomerase. This indicated that the glycolytic enzymes responsible for the catalysis of Fructose 1.6-bisphosphate to 3-phosp hoglycerate were inhibited, However, in spite of the expected reductio n in acid production intracellularly, the intracellular pH actually de creased in the presence of sodium ions. It is possible that the low in tracellular pH inhibits the activity of the glycolytic enzymes involve d in the breakdown of fructose 1,6-bisphosphate to 3-phosphoglycerate.