Engineering <i>Escherichia coli</i> for Anaerobic Succinate Fermentation Using Corn Stover Hydrolysate as a Substrate

Succinic acid is regarded as one of the most important platform chemicals used in materials science, chemistry, and food industrial applications. Currently, the main bottlenecks in the microbial succinate synthesis lie in the low titer, cofactor imbalance, and high production costs. To overcome these challenges, the reductive tricarboxylic acid cycle (TCA) and glucose uptake pathway were enhanced, increasing the titer of succinate to 4.31 g/l, 2.06-fold of the original strain. Furthermore, formate dehydrogenase from <i>Candida boidinii</i> was simultaneously overexpressed to increase the regeneration of NADH which was deficient in succinate synthesis under anaerobic condition. On this basis, the oxygen-responsive biosensor was used to replace the isopropyl-β-d-thiogalactoside (IPTG)-induction system, enabling strain to avoid the utilization of IPTG for succinate production. Using corn stover hydrolysate as the substrate, the optimum strain produced 60.74 g/l succinate in 5 L bioreactor. The engineered strain exhibited high succinate titer using biomass hydrolysate as substrate, significantly reduced the fermentation cost.