Study of acid production and growth of oral streptococci under low pH and strictly anaerobic conditions.

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1. Production of formic arid acetic acids by Streptococcus mutatis JC2 decreased and lactic acid increased when the pH of culture medium lowered from 7.0 to 5.5. even under glucose-limitation and strictly anaerobic conditions. Two mechanisms seemed to be involved in the increased production of lactic acid at extracellular pli of 5.5. Firstly, lactate dehydrogenase(LDH) had a higher activity than pyruvate formate-lyase(PFL) in the cells. Secondly, the amount of LDH was increased remarkably in comparison to that of PFL during growth at pH 5.5.2. Anaerobic glycolysis of Streptococcus sanguis ATCC 10556 was inhibited more strongly by fluoride than aerobic glycolysis. The cells of S. sanguis had lower pliosphoenolpyruvate(PEP) potential(intracellular levels of 3-phosphoglycerate, 2-phosphoglycerate and phosphoenolpyruvate) under anaerobic conditions than aerobic conditions. Thus it was suggested that the low PEP potential accounted for the reduced transport of sugar by the PEP-dependent phosphotransport system and consequently the reduced glycolysis of the microorganism under anaerobic conditions.3. The acid produced by streptococci during their sugar metabolism was estimated with a pH-stat and a carboxylic acid analyzer. The amount of titratable acid estimated by the alkaline titration with the pH-stat was larger than the amount of total carboxylic acids estimated with the carboxylic acid analyzer. The results indicated that streptococci produced not only carboxylic acids, such as lactic, formic and acetic acid, but also non-carboxylic acid(s).