초록
A novel Saccharomyces cerevisiae whole-cell biocatalyst for xylitol production based on Candida tenuis xylose reductase (CtXR) is presented. Six recombinant strains expressing wild-type CtXR or an NADH-specific mutant were constructed and evaluated regarding effects of expression mode, promoter strength, biocatalyst concentration and medium composition. Intracellular XR activities ranged from 0.09Umg<SUB>Prot</SUB><SUP>-1</SUP> to 1.05Umg<SUB>Prot</SUB><SUP>-1</SUP> but did not correlate with the strains' xylitol productivities, indicating that other factors limited xylose conversion in the high-activity strains. The CtXR mutant decreased the biocatalyst's performance, suggesting use of the NADPH-preferring wild-type enzyme when (semi-)aerobic conditions are applied. In a bioreactor process, the best-performing strain converted 40gL<SUP>-1</SUP> xylose with an initial productivity of 1.16gL<SUP>-1</SUP>h<SUP>-1</SUP> and a xylitol yield of 100%. The obtained results underline the potential of CtXR wild-type for xylose reduction and point out parameters to improve ''green'' xylitol production.