Succinic Acid Production By Engineered Escherichia Coli Using Xylose Mother Liquor

Succinic acid(1, 4-butanedioic acid) is identified as one of the important buildingblock chemicals which widely used in many fields including food, pharmaceutical, surfactants, detergents, green solvents and biodegradable plastics. Biomass is one of the most abundant and low-cost renewable resources. The microbial fermentation of biomass to succinic acid has been testified as an environmentally friendly and energy-efficient process during the last decades.In this study, the industrial residues, xylose mother liquor was used to produce succinic acid by anaerobic fermentation using recombinant Escherichia coli strain SD121, and the response surface methodology was used to optimize the fermentation conditions to achieve high-level production of succinic acid.Firstly, the main composition of reducing sugar in xylose mother liquor was analyzed. The reducing sugar concentration detected by HPLC contained: 394.4 g L-1 xylose, 127.4 g L-1 L arabinose, 104.7 g L-1 glucose, 85.3 g L-1 galactose, and a trace of unknown sugars(probably mannose, rhamnose, and oligosaccharides). In this study, the method of overliming(Ca(OH)2 treatments), evaporation and ion-exchange were executed to reduce the inhibitors in xylose mother liquor. The results showed that the overliming functioned best. The maximum production of succinic acid was 23.20 g L-1 with a yield of 0.58 g g-1 total sugar using the basic medium.Then the fermentations of Escherichia coli SD121 using various concentrations of xylose, L-arabinose, glucose and galactose individually and mixed sugars were examined to see its ability to produce succinic acid. Results showed that Escherichia coli SD121 could efficiently metabolize xylose, L-arabinose, glucose and galactose to produce succinic acid and could consume them simultaneously in the mixed sugar fermentation. The maximum production of succinic acid was 35.5 g L-1 after 64 h when the initial total sugar concentration was 50 g L-1.The optimal conditions of succinic acid fermentation were as follows: 82.62 g L-1 total initial sugars, 42.27 g L-1 Mg CO3, and 17.84 g L-1 yeast extract. The maximum production of succinic acid was 52.09 g L-1 after 84 h with a yield of 0.63 g g-1 total sugar, similar to the predicted value(53.18 g L-1). It was 1.78-fold of the production of that obtained with the basic medium. This was the ?rst report on succinic acid production from xylose mother liquor by recombinant E. coli strains with media optimization using response surface methodology. This work suggested that the xylose mother liquor could be an alternative renewable substrate for the economical production of succinic acid by recombinant E. coli strains.