Effect of extra- and intracellular sources of CO2 on anaerobic utilization of glucose by Escherichia coli strains deficient in carboxylation-independent fermentation pathways

Resumo

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.