4. Conclusions
CRISPR-Cpf1 genome editing system is an efficient recombination technology to generate knock-out mutants of the lactate dehydrogenase 1 gene to enhance succinic acid production. The ΔldhA-6 mutant produced 14.82 g L-1succinic acid production over 6 h, equating to a 2.47 g L-1 h-1 productivity in the fermentation of 4% hydrolysate, with an 86.2% glucose and 20% xylose consumption. Under the same fermentation conditions, the transformant [Psod:sucE- ΔldhA ] showed a productivity of 2.95 g L-1 h-1 and produced approximately 39.67 g L-1 succinic acid over 48 h in the fed-batch process. The yield of succinic acid from the hydrolysate when only considering glucose consumption during the fed-batch fermentation is approximately 84.4%. Xylose consumption was slower than glucose and still remained throughout the fermentation. By diminishing the sugar loss during enzymatic hydrolysis and the fermentation processes, the production of succinic acid will likely be enhanced in the future.