Production of d-Xylonate from Corn Cob Hydrolysate by a Metabolically Engineered Escherichia coli Strain
2018
Zhang, Yipeng | Guo, Shiting | Wang, Yuxian | Liang, Xiao | Xu, Ping | Gao, Chao | Ma, Cuiqing
Corn cob is the secondary agricultural residue that can be easily hydrolyzed into hydrolysate with abundant d-xylose. Besides d-xylose, d-glucose, and l-arabinose are also utilizable sugars in corn cob hydrolysate. Here, we established a coutilization system through which recombinant Escherichia coli can use d-glucose and l-arabinose supporting its growth and convert d-xylose in corn cob hydrolysate into d-xylonate. First, biosynthetic pathway of d-xylonate was overexpressed and two xylonate dehydratases were knocked out in E. coli W3110 to enhance d-xylonate production from d-xylose. Then, the genes responsible for acetate, ethanol, and lactate synthesis were knocked out to decrease these byproducts production during the growth of the recombinant strain. Three successive strategies were employed to enhance the d-xylonate production—using lactose as the inducer, eliminating carbon catabolite repression, and inactivating the lactose degradation. Finally, 108.2 g/L d-xylonate was produced with a yield of 1.09 g of d-xylonate/g of d-xylose using d-xylose as the substrate and d-glucose as the carbon source through fed-batch fermentation. When corn cob hydrolysate was used, 91.2 g/L d-xylonate was produced with a specific productivity of 1.52 g/[L·h]. This study is valuable not only for producing d-xylonate but also for providing a coutilization system to obtain other important chemicals from corn cob hydrolysate.
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