Enhanced anaerobic succinic acid production by Escherichia coli NZN111 aerobically grown on gluconeogenic carbon sources

Escherichia coli strain NZN111, a pflB and ldhA double mutant of E. coli W1485, is considered a candidate of succinic acid producer. However, it is reported that this strain fails to ferment glucose anaerobically. In this study, it was demonstrated that when a gluconeogenic carbon source was used to replace glucose in aerobic culture, the NZN111 cells restored the ability to ferment glucose in the subsequent anaerobic culture with succinic acid as the major product even though no further genetic manipulation had been carried out. Activities of enzymes including phosphoenolpyruvate (PEP) carboxykinase, PEP carboxylase, isocitrate lyase, malate dehydrogenase, malic enzyme, and pyruvate kinase in the NZN111 cells aerobically grown on different carbon sources were measured, and enhanced anaplerotic and oxaloacetate-reducing activities were revealed. Furthermore, supply of MgCO3 or NaHCO3 greatly improved succinate production by the malate-grown NZN111 cells. At the same time, pyruvic acid production was significantly reduced. When the malate-grown cells were anaerobically cultured in a salt medium with high pH buffering capacity, succinic acid was produced at a specific productivity of 308 mg/(g DCW h) with a molar yield of 1.31 mol succinic acid/mol glucose.