NAD⁺-dependent xylitol dehydrogenase (xdhA) and L-arabitol-4-dehydrogenase (ladA) deletion mutants of Aspergillus oryzae for improved xylitol production.

Xylitol dehydrogenase (XDHA) and L-arabitol dehydrogenase (LADA) are two key enzymes in xylan metabolism catalyzing the oxidation of xylitol to D-xylulose and arabitol to L-xylulose, respectively. In Aspergillus oryzae, XDHA and LADA are encoded by xdhA and ladA. We deleted xdhA and ladA and xdhA-ladA to generate mutants with decreased dehydrogenase activities and increased xylitol production. The mutants were constructed by homologous transformation into A. oryzae P4 (∆pyrG) using pyrG as a selectable marker. The xylitol productivity of the mutants was measured using D-xylose as the sole carbohydrate source. xdhA, ladA, and the double-deletion mutant produced, respectively, 12.4 g xylitol/l with a yield of 0.24 g/g D-xylose, 12.4 g/l with a yield of 0.33 g/g D-xylose, and 8.6 g/l at a yield of 0.26 g/g D-xylose.