Metabolic Engineering of Escherichia coli Cells for Ethanol Production under Aerobic Conditions

The ethanol production by recombinant Escherichia coli introducing of pyruvate decarboxylase (pdc) and alcohol dehydrogenase (adhB) from Zymomonas mobilis was investigated under aerobic conditions. In aerobic culture (KLa = 1.5 min-1), the cells expressing pdc and adhB produced 0.4 g l-1 ethanol when cultured for 18 h. This value was improved in BW25113Δpta/pHfdh/pTadhB-pdc following 4 g l-1 formate feeding at 0.8 g l-1 ethanol. In higher oxygenation level (KLa = 6.1 min-1), the production of ethanol was further enhanced at 1.79 g l-1 ± 0.37 g l-1 after 24 h cultivation. Formate was found not detectable at the end of culture, indicating complete degradation this organic acid to regenerate NADH from NAD+. The culture strategy was effective to inactivate lactate dehydrogenase, which is major competitor for ethanol production in utilizing NADH.