Effects of xylitol dehydrogenase (XYL2) on xylose fermentation by engineered Candida glycerinogenes

Abstract

Efficient bioconversion of d-xylose into various biochemicals is critical for lignocelluloses application. Candida glycerinogenes, expressing the xylitol dehydrogenase (XYL2) gene, has the ability to produce glycerol from xylose entered into pentose phosphate pathway. In this study, we demonstrate that low expression levels of the XYL2 gene derived from Scheffersomyces stipitis in C. glycerinogenes is a major bottleneck in efficient xylose fermentation. Through a metabolic engineering approach using an integrative expression, XYL2 was identified as an overexpression target for improving xylose metabolism. Two recombinant strains with XYL2 overexpression were constructed to ferment a mixture of glucose and xylose simultaneously in batch fermentation. Compared with C. glycerinogenes (wild type), glycerol production from xylose by C. glycerinogenes (PURGAPX2) and C. glycerinogenes (PURGPDX2) was increased by 94.5% and 103.3%, respectively. It was also found that additional overexpression of XYL2 under the control of strong promoters in a xylose-fermenting strain not only reduced xylitol accumulation but also increased glycerol yields. As the expression levels of XYL2 increased, the glycerol yields gradually improved from 30.6 to 63.3 g/L, whereas the xylitol yields significantly decreased from 38.7 to 19.9 g/L. These results suggest that strong expression of XYL2 is a necessary condition for developing efficient xylose-fermenting strains.

Glycerol Production from Undetoxified Lignocellulose Hydrolysate by a Multiresistant Engineered Candida glycerinogenes

“…Previous studies by the team have modified C. glycerinogenes for different xylose metabolism, but none of them were as effective as the present study. , Especially in the hydrolysate, the modified C. glycerinogenes in this study had a greater advantage.…”

“…This indicates that overexpression of SsXYL1, SsXYL2, SsXKS1, and CgHXT4.2AS can increase the xylose metabolism rate and biomass, thereby further improving the xylose metabolism of glycerinogenes for different xylose metabolism, but none of them were as effective as the present study. 26,34 Especially in the hydrolysate, the modified C. glycerinogenes in this study had a greater advantage.…”

Primary metabolites from overproducing microbial system using sustainable substrates

“…The higher expression levels of XYL 2 increased the glycerol yields (30.6–63.3 g⋅L −1 ) with decreased xylitol yields (38.7–19.9 g⋅L −1 ). Therefore, a higher expression level of xyl2 in efficient xylose‐fermenting strains is a necessary condition [103].…”

Bioethanol a Microbial Biofuel Metabolite; New Insights of Yeasts Metabolic Engineering

“…Candida glycerinogenes, expressing the xylitol dehydrogenase (XYL2) gene, and can produce glycerol from xylose that has observable role in pentose phosphate pathway. Minimal expression levels of the XYL2 gene originated from Scheffersomyces stipitis in C. glycerinogenes has a distinguished role in enhancing the efficiency of xylose fermentation [145]. An engineered strain that has both wild XR and mutant XR showed lower xylitol accumulation and faster xylose consumption than engineered strains overexpressing only one type of XRs.…”