Effects of redox potential control on succinic acid production by engineered Escherichia coli under anaerobic conditions

The effects of oxido-reduction potential (ORP) control on succinic acid production have been investigated in Escherichia coli LL016. In LL016, two CO₂ fixation pathways were achieved and NAD⁺ supply was enhanced by co-expression of heterologous pyruvate carboxylase (PYC) and nicotinic acid phosphoribosyltransferase (NAPRTase). During anaerobic fermentation, cell growth and metabolite distribution were changed with redox potential levels in the range of -200 to -400 mV. From the results, the ORP level of -400 mV was preferable, which resulted in the high succinic acid concentration (28.6 g/L) and high succinic acid productivity (0.33 g/L/h). Meanwhile, the yield of succinic acid at the ORP level of -400 mV was 39% higher than that at the ORP level of -200 mV. In addition, a higher NADH/NAD ⁺ ratio and increased enzyme activities were also achieved by regulating the culture to a more reductive environment, which further enhanced the succinic acid production.