Evaluation of Anaerobic Glucose Utilization by Escherichia coli Strains with Impaired Fermentation Ability during Respiration with External and Internal Electron Acceptors

The characteristics of anaerobic glucose utilization and metabolite production by recombinant Escherichia coli strains with impaired fermentation ability during respiration with pyruvate as an internal electron acceptor and nitrate as an external one have been studied. It was found that respiration processes utilizing pyruvic acid as an endogenous electron acceptor and leading to lactate and alanine formation were capable of mutual interference. After excluding ammonium ions from the medium, the native activity levels of respiratory lactate dehydrogenases Dld and LldD in E. coli strains deficient in mixed acid fermentation pathways can almost completely compensate for the loss of activity of the respiratory alanine dehydrogenase DadA, but they are insufficient for the maintenance of the entire intracellular redox balance. The addition of nitrate ions to the medium abolished alanine production by the strains, despite the availability of ammonium ions, while the functionality of the respiratory reduction of endogenous pyruvate to lactate is retained in the studied strains, even in the presence of a strong exogenous oxidant. Respiration with an external electron acceptor provoked activation of the oxidative tricarboxylic acid cycle in the strains. The anaerobic utilization of glucose by the strain with an interrupted tricarboxylic acid cycle increased during nitrate respiration but remained restricted by the excessive generation of reducing equivalents in the residual reactions of the cycle.