Bioconversion of D-xylose to D-xylonate with Kluyveromyces lactis

D-Xylonate was produced from D-xylose using Kluyveromyces lactis strains which expressed the gene for NADP(+)-dependent D-xylose dehydrogenase from Trichoderma reesei (xyd1). Up to 19 +/- 2 g D-xylonate l(-1) was produced when K. lactis expressing xyd1 was grown on 10.5 g D-galactose l (1) and 40 g D-xylose l (1). Intracellular accumulation of D-xylonate (up to similar to 70 mg [g biomass](-1)) was observed. D-Xylose was metabolised to D-xylonate, xylitol and biomass. Oxygen could be reduced to 6 mmol O(2) l(-1) h(-1) without loss in titre or production rate, but metabolism of D-xylose and xylitol were more efficient when 12 mmol O(2) l(-1) h(-1) were provided. D-Xylose uptake was not affected by deletion of either the D-xylose reductase (XYL1) or a putative xylitol dehydrogenase encoding gene (XYL2) in xyd1 expressing strains. K. lactis xyd1 Delta XYL1 did not produce extracellular xylitol and produced more D-xylonate than the xyd1 strain containing the endogenous XYL1. K. lactis xyd1 Delta XYL2 produced high concentrations of xylitol and significantly less D-xylonate than the xyd1 strain with the endogenous XYL2. (C) 2011 Elsevier Inc. All rights reserved.