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Metabolism of intracellular polysaccharide in the cells of Streptococcus mutans under strictly anaerobic conditions.

Streptococcus mutans, which had accumulated glycogen-like iodophilic intracellular polysaccharide (IPS), produced large amounts of formate, acetate and ethanol from the IPS by pyruvate formate-lyase (PFL) under strictly anaerobic conditions without exogenous sugar. Under aerobic conditions, the same S. mutans produced exclusively lactate and pyruvate from the IPS because of the inactivation of PFL by oxygen. The total amount of acid produced under anaerobic conditions was larger than that under aerobic conditions. The analysis of intracellular glycolytic intermediates revealed that levels of fructose 1,6-bisphosphate (lactate dehydrogenase (LDH) activator) and glyceraldehyde 3-phosphate and dihydroxyacetone phosphate (PFL inhibitors) were low when IPS was used as a glycolytic substrate, implying that PFL functions more efficiently than LDH in IPS metabolism. These findings suggest that the PFL pathway contributes to the acid production from IPS, and may explain partially why the acids in starved dental plaque are mainly acetate and formate.