Genetic reconstruction of the aerobic central metabolism in Escherichia coli for the absolute aerobic production of succinate.

Most reported efforts to enhance production of the industrially valuable specialty chemical succinate have been done under anaerobic conditions, where E. coli undergoes mixed-acid fermentation. These efforts have often been hampered by the limitations of NADH availability, poor cell growth, and slow production. An aerobic succinate production system was strategically designed that allows E. coli to produce and accumulate succinate efficiently and substantially as a product under absolute aerobic conditions. Mutations in the tricarboxylic acid cycle (sdhAB, icd, iclR) and acetate pathways (poxB, ackA-pta) of E. coli were created to construct the glyoxylate cycle for aerobic succinate production. Experiments in flask studies showed that 14.28 mM of succinate could be produced aerobically with a yield of 0.344 mole/mole using 55 mM glucose. In aerobic batch reactor studies, succinate production rate was faster, reaching 0.5 mole/mole in 24 h with a concentration of 22.12 mM; further cultivation showed that succinate production reached 43 mM with a yield of 0.7. There was also substantial pyruvate and TCA cycle C(6) intermediate accumulation in the mutant. The results suggest that more metabolic engineering improvements can be made to this system to make aerobic succinate production more efficient. Nevertheless, this aerobic succinate production system provides the first platform for enhancing succinate production aerobically in E. coli based on the creation of a new aerobic central metabolic network.