Efficient production of xylitol from hemicellulosic hydrolysate using engineered Escherichia coli

Abstract

A metabolically engineered Escherichia coli has been constructed for the production of xylitol, one of the top 12 platform chemicals from agricultural sources identified by the US Department of Energy. An optimal plasmid was constructed to express xylose reductase from Neurospora crassa with almost no inclusion bodies at relatively high temperature. The phosphoenolpyruvate-dependent glucose phosphotransferase system (ptsG) was disrupted to eliminate catabolite repression and allow simultaneous uptake of glucose and xylose. The native pathway for D-xylose catabolism in E. coli W3110 was blocked by deleting the xylose isomerase (xylA) and xylulose kinase (xylB) genes. The putative pathway for xylitol phosphorylation was also blocked by disrupting the phosphoenolpyruvate-dependent fructose phosphotransferase system (ptsF). The xylitol producing recombinant E. coli allowed production of 172.4gL−1 xylitol after 110h of fed-batch cultivation with an average productivity of 1.57gL−1h−1. The molar yield of xylitol to glucose reached approximately 2.2 (mol xylitol mol−1 glucose). Furthermore, the recombinant strain also produced about 150gL−1 xylitol from hemicellulosic sugars in modified M9 minimal medium and the overall productivity was 1.40gL−1h−1, representing the highest xylitol concentration and productivity reported to date from hemicellulosic sugars using bacteria. Thus, this engineered E. coli is a candidate for the development of efficient industrial-scale production of xylitol from hemicellulosic hydrolysate.