Effect of Bicarbonate on the Growth of Actinobacillus actinomycetemcomitans in Anaerobic Fructose-limited Chemostat Culture

Abstract

Summary: The effect of bicarbonate on the growth and product formation by a periodontopathic bacterium, Actinobacillus actinomycetemcomitans, was examined in an anaerobic chemostat culture with fructose as the limiting nutrient. The chemostat cultures were run at dilution rates between 0·04 and 0·25 h−1and the maximum growth yield (Y fructose max) was estimated to be 40·3 and 61·7 g dry wt (mol fructose)−1in the absence and presence of bicarbonate, respectively. The major fermentation products in the absence of bicarbonate were formate, acetate, ethanol and succinate, with small amounts of lactate. The addition of bicarbonate to the medium resulted in a marked decrease in ethanol production and in a significant increase in succinate production. Washed cells possessed activity for the cleavage of formate to CO2 and H2, which seemed to play a role in supplying CO2 for the synthesis of succinate in the absence of bicarbonate. The study of enzyme activities in cell-free extracts suggested that fructose was fermented by the Embden-Meyerhof-Parnas pathway. The values of Y ATP maxand the efficiency of ATP generation (ATP-Eff) during fructose catabolism were estimated and higher values were obtained for the culture in the presence of bicarbonate: 20·2 g dry wt (mol ATP)−1and 30 mol ATP (mol fructose)−1, respectively, versus Y ATP max = 15·1 and ATP-Eff = 2·7 in the absence of bicarbonate.