Production of xylitol from d-xylose and glucose with recombinant Corynebacterium glutamicum

The product spectrum of a soil bacterium Corynebacterium glutamicum was extended to include a functional sugar xylitol. The recombinant C. glutamicum, engineered to express the xylose reductase gene XYL1of Pichia stipitis, produced xylose reductase with a specific activity of ca. 0.6 U/mg protein. Due to the absence of xylose isomerase and xylitol dehydrogenase genes, loose catabolite repression, high NADPH regeneration capacity, and tolerance against sugar-induced osmotic stress, the recombinant biocatalyst was able to efficiently produce xylitol from d-xylose using glucose as source of reducing equivalents. A fed-batch culture-based biotransformation allowed xylitol to accumulate to a concentration of 34.4 g/L (226 mM) in the medium with the specific productivity and product yield of xylose of 0.092 g/g dry cells/h and over 97%, respectively. The molar yield of xylitol to energy source during the biotransformation reached approximately 1.6 mol of xylose/mol of glucose.