Abstract
The effect of extra- and intracellular CO2 sources on anaerobic glucose utilization by Escherichia coli strains deficient in the main pathways of mixed acid fermentation and possessing a modified system of glucose transport and phosphorylation was studied. Intracellular CO2 generation in the strains was ensured resulting from the oxidative decarboxylation of pyruvic acid by pyruvate dehydrogenase. Endogenous CO2 formation by pyruvate dehydrogenase stimulated anaerobic glucose consumption by the strains due to the involvement in the fermentation process of condensation reactions between oxaloacetic acid and acetyl-CoA. The availability of an external CO2 source (dissolved in medium sodium bicarbonate) promoted utilization of carbohydrate substrate by favoring the predominant participation in the fermentation of reactions directly dependent on phosphoenolpyruvate carboxylation. The positive effect of the availability of exogenous СО2 was sharply decreased in recombinant strains with the impaired functionality of the reductive branch of the tricarboxylic acid cycle. As a result, intracellular СО2 generation coupled to acetyl-CoA formation promoted anaerobic glucose utilization by cells of the corresponding mutants more markedly than the presence in the medium of dissolved sodium bicarbonate.
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