Metabolic engineering of d-xylose pathway in Clostridium beijerinckii to optimize solvent production from xylose mother liquid

Clostridium beijerinckii is an attractive butanol-producing microbe for its advantage in co-fermenting hexose and pentose sugars. However, this Clostridium strain exhibits undesired efficiency in utilizing d-xylose, one of the major building blocks contained in lignocellulosic materials. Here, we reported a useful metabolic engineering strategy to improve d-xylose consumption by C. beijerinckii. Gene cbei2385, encoding a putative d-xylose repressor XylR, was first disrupted in the C. beijerinckii NCIMB 8052, resulting in a significant increase in d-xylose consumption. A d-xylose proton-symporter (encoded by gene cbei0109) was identified and then overexpressed to further optimize d-xylose utilization, yielding an engineered strain 8052xylR-xylT(ptb) (xylR inactivation plus xylT overexpression driven by ptb promoter). We investigated the strain 8052xylR-xylT(ptb) in fermenting xylose mother liquid, an abundant by-product from industrial-scale xylose preparation from corncob and rich in d-xylose, finally achieving a 35% higher Acetone, Butanol and Ethanol (ABE) solvent titer (16.91g/L) and a 38% higher yield (0.29g/g) over those of the wild-type strain. The strategy used in this study enables C. beijerinckii more suitable for butanol production from lignocellulosic materials.