Xylitol production by NAD+-dependent xylitol dehydrogenase (xdhA)- and l-arabitol-4-dehydrogenase (ladA)-disrupted mutants of Aspergillus oryzae

Aspergillus oryzae can metabolize xylan to d-xylose and d-xylose to xylitol. However, accumulation of xylitol is controlled by dehydrogenases, such as xylitol dehydrogenase (XDH) and l-arabitol-4-dehydrogenase (LAD), and fluxed into the pentose phosphate pathway. In A. oryzae, XDH and LAD are encoded by xdhA and ladA, respectively. We disrupted the xdhA and ladA genes individually in an attempt to increase xylitol production. The xdhA- and ladA-disrupted mutants were constructed by homologous transformation into A. oryzae P5 (ΔpyrG), and pyrG was used as a selectable marker. The mutants were grown on different carbohydrate-containing media, colony diameters of mutants were measured, and gene disruption was confirmed by PCR. The xylitol productivity of the mutants was measured using d-xylose and oat spelt xylan as the sole sources of carbohydrates. The xdhA-disrupted mutant xdhA2-1 produced 16.6 g/L xylitol at a yield of 0.43 g/g d-xylose and productivity of 0.248 g/L. h from d-xylose, while 10.2 g/L xylitol was produced at a yield of 0.204 g/g xylan from oat spelt xylan.