Production of Xylitol from d -Xylose by a Xylitol Dehydrogenase Gene-Disrupted Mutant of Candida tropicalis

Abstract

ABSTRACT Xylitol dehydrogenase (XDH) is one of the key enzymes in d -xylose metabolism, catalyzing the oxidation of xylitol to d -xylulose. Two copies of the XYL2 gene encoding XDH in the diploid yeast Candida tropicalis were sequentially disrupted using the Ura-blasting method. The XYL2 -disrupted mutant, BSXDH-3, did not grow on a minimal medium containing d -xylose as a sole carbon source. An enzyme assay experiment indicated that BSXDH-3 lost apparently all XDH activity. Xylitol production by BSXDH-3 was evaluated using a xylitol fermentation medium with glucose as a cosubstrate. As glucose was found to be an insufficient cosubstrate, various carbon sources were screened for efficient cofactor regeneration, and glycerol was found to be the best cosubstrate. BSXDH-3 produced xylitol with a volumetric productivity of 3.23 g liter −1 h −1 , a specific productivity of 0.76 g g −1 h −1 , and a xylitol yield of 98%. This is the first report of gene disruption of C. tropicalis for enhancing the efficiency of xylitol production.