Metabolic engineering of aerobic succinate production systems in Escherichia coli to improve process productivity and achieve the maximum theoretical succinate yield.

The potential to produce succinate aerobically in Escherichia coli would offer great advantages over anaerobic fermentation in terms of faster biomass generation, carbon throughput, and product formation. Genetic manipulations were performed on two aerobic succinate production systems to increase their succinate yield and productivity. One of the aerobic succinate production systems developed earlier (Biotechnol, Bioeng., 2004, accepted) was constructed with five mutations (DeltasdhAB, Deltaicd, DeltaiclR, DeltapoxB, and Delta(ackA-pta)), which created a highly active glyoxylate cycle. In this study, a second production system was constructed with four of the five above mutations (DeltasdhAB, DeltaiclR, DeltapoxB, and Delta(ackA-pta)). This system has two routes in the aerobic central metabolism for succinate production. One is the glyoxylate cycle and the other is the oxidative branch of the TCA cycle. Inactivation of ptsG and overexpression of a mutant Sorghum pepc in these two production systems showed that the maximum theoretical succinate yield of 1.0 mol/mol glucose consumed could be achieved. Furthermore, the two-route production system with ptsG inactivation and pepc overexpression demonstrated substantially higher succinate productivity than the previous system, a level unsurpassed for aerobic succinate production. This optimized system showed remarkable potential for large-scale aerobic succinate production and process optimization.