SUMMARY: The anaerobic fermentation of glucose by ATCC 7068 was studied in batch culture with and without pH control. The fermentation was characterized by two distinct metabolic phases. In the primary growth phase, the concentrations of ethanol and acetic acid increased exponentially, and formate was detected as a minor product. The secondary phase was marked by a slowing and eventual cessation of growth, along with the disappearance of formate and acetate, and the appearance of H, CO, and acetone. Exogenously-added substrates were converted with stoichiometries of 1 formate → 1 H + 1 CO, and approximately 2 acetate → 1 acetone. Consumption of > 8g glucose 1 required exogenous pH control, and acetone formation was strongly pH-dependent. Glucose was fermented by the Embden-Meyerhof pathway. Cell extracts contained pyruvate formate-lyase and formate dehydrogenase activities, but only low pyruvate dehydrogenase activity. A balanced fermentation pathway is presented which is consistent with reaction stoichiometries and [14C]glucose labelling data in whole cultures, and with enzyme activities in extracts. The pathway is compared with those of other facultative anaerobes and the acetone-producing


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