(512d) Enhanced Succinic Acid Production by Lactose-Induced Expression of Phosphoenolpyruvate Carboxylase in Ptsg Mutant Escherichia Coli

Succinic acid is a C4 dicarboxylic acid, which is considered as one of the top value-added chemicals produced from biomass. Recombinant Escherichia. coli strains with homologous or heterogenous genes under the IPTG inducible promoters lac, tac, and trc showed great potential for succinic acid fermentation. The promoters mentioned above can also be induced by the addition of lactose, which is often added into the medium without glucose to avoid the carbon catabolite repression (CCR). However, this induction strategy conflicts with the condition of succinic acid fermentation processed in glucose-medium. So lactose had not been used to instead of IPTG in succinic acid fermentation before. In this work, a fermentation process for the production of succinic acid by recombinant E. coli using lactose as inducer was developed. The efficient utilization of lactose as inducer was demonstrated in batch cultures of the ptsG, ldh and pfl mutant DC1515 harboring expression vector containing the ppc gene, which encodes the homologous phosphoenolpyruvate carboxylase (PEPC). Addition of lactose to the concentration of 1 g l-1 at the middle log phase can induce ppc to a suitable level. In anaerobic culture carried out in flasks, succinic acid was produced at a level of 14.86 g l-1 from 15 g l-1 glucose with a succinic acid yield of 1.51 mol mol-1 glucose. In two-stage culture carried out in a 2.5-l fermentor, the overall yield and concentration of succinic acid reached to 1.27 mol mol-1 glucose and 31.64 g l-1, respectively, with a productivity of 1.1 g l-1 h-1 in the anaerobic stage. The efficient utilization of lactose as inducer makes recombinant E. coli a more promising strain for succinic acid production at industrially scale.