Characterization of Anaerobic Central Metabolism to Improve Succinate Production in Enterobacter Aerogenes

Succinate is a core biochemical building block, and optimizing production by microbial fermentation from biomass is a focus of basic and applied biotechnology research. Lowering pH in anaerobic succinate fermentation culture is a cost-effective and environment-friendly approach to reducing the use of sub-raw materials such as alkali, which are needed for neutralization. To perform succinate fermentation under acidic (below pH 6.0) and anaerobic conditions, we selected and characterized anaerobic metabolism in a newly isolated Enterobacter aerogenes strain that rapidly assimilates glucose at pH 5.0. Single-gene knockout studies showed that the ethanol synthesis pathway serves as the dominant NADH re-oxidation pathway in this organism. We also generated a ΔadhE/PCK strain to eliminate ethanol formation, and introduced a heterogeneous carboxylation enzyme. The strain produced succinate from glucose with a 60.5% yield (grams of succinate produced per gram of glucose consumed) at pH 5.4 and anaerobic conditions.