Multidimensional Engineering of Xylose Metabolism for Improving Poly(3-hydroxybutyrate) Synthesis from Corn Stover Hydrolysate in Recombinant Escherichia coli

Glucose and xylose constitute the primary components of lignocellulose. Enhancing the efficient utilization of both sugars can improve the bioproduction efficiency. This work constructed an engineered Escherichia coli with improved capability to coutilize glucose and xylose from corn stover hydrolysate (CSH). First, carbon catabolite repression was eliminated to relieve the glucose-mediated inhibition of xylose metabolism. Then, the expression levels of key rate-limiting genes tktA and xylB were optimized to enhance xylose metabolic flux. Finally, to reduce metabolic crosstalk, xylose isomerase was targeted to the periplasm, further improving xylose assimilation. The resulting optimized strain, AM28, exhibited enhanced xylose utilization and acetyl-CoA derivative synthesis from CSH. Subsequently, AM28 was transformed with plasmids harboring phaCAB genes derived from Cupriavidus necator H16 to produce poly(3-hydroxybutyrate) (PHB). Strain AM28 (phaCAB) produced 3.2 g/L PHB with a yield of 0.15 g/g from CSH, which was higher than that of control strain AM29 (0.5 g/L; 0.02 g/g). Interestingly, the PHB from strain AM28 (phaCAB) showed improved physical properties in crystallinity, thermostability, and molecular weight. Our study provided insights into the utilization of CSH for PHB synthesis.