Efficient Production of Succinic Acid From Corn Stalk Hydrolysate by Recombinant Escherichia Coli Strain with PtsG Mutation

Succinic acid, a C4 dicarboxylic acid, is considered as one of the top value-added chemicals produced from biomass. Exploitation of biomass, other than cornstarch, for the production of succinic acid requires a microbial type that can ferment the mixture of sugars derived from lignocellulose. The ptsG mutant Escheichia coli strain gained the ability to ferment glucose and xylose/arabinose simultaneously, while the ptsG+ metabolized glucose in preference to other sugars, showing delayed and incompletely pentose utilization. Rcombinant E. coli strains with ptsG mutation were engineered for succinate fermentation. The concentration of sugar mixtures were varied to test the efficiency of sugar utilization by the ldhA, pflB, ptsG mutant strain with ppc gene from cyanobacterium sp. 7120 encoding the phosphoenolpyruvate carboxylase. The best result of this strain was a yield of 0.73 g succinate g-1 sugar, when fermenting a 40 g l-1 total mixture of glucose and xylose. With a modeled corn stalk hydrolysate containing 30 g l-1 glucose, 10 g l-1 xylose and 2.5 g l-1 arabinose, the strain finally reached a similar yield of 0.77 g g-1 sugar. The deficient of ptsG was found to decrease the glucose uptake rate, while the ppc expression induced by IPTG partly remedied this objection. To further test this strain's ability, fermentation of corn stalk hydrolysate was also carried out and a succinate yield of 0.81 g g-1 sugar was achieved. The recombinant E. coli strain could ferment pentose and glucose simultaneously and efficiently, and facilitate the succinate production from corn stalk hydrolysate.