Enhancement of lactate and succinate formation in adhE or pta-ackA mutants of NADH dehydrogenase-deficient Escherichia coli

Aims: The aim of the study is to investigate the effect of multiple mutations in redox or energy producing pathways of Escherichia coli on metabolic product distribution in anaerobic-rich media cultures. Methods and Results: Various combinations of NADH dehydrogenase (NDH)-deficient, alcohol dehydrogenase (ADH), and phosphotransacetylase and acetate kinase (PTA-ACK) mutants were constructed. Anaerobic LB-glucose cultures of the strains were grown and extracellular metabolites were analysed and compared with those of the parental strain, E. coli MG1655. The profile of metabolites was examined in log phase and 24-h cultures. Conclusions: Inactivation of ndh and/or nuo gene leads to higher production of D-lactate, ethanol, formate and succinate in log phase. Inactivation of pta-ackA in NDH-I- or NDH-II-deficient strains lead to increased D-lactate formation and decreased ethanol formation. Removal of ethanol production by adhE gene inactivation generated higher production of succinate and D-lactate. D-lactate was the primary product in the ndh nuo adhE strain. Significance and Impact of the Study: The results show the effects of altering NADH utilization pathways on distribution of metabolic products. Such information improves our understanding of metabolic shifts and may find application in metabolic engineering of E. coli.