Abstract
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 ∼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 xyd1Δ XYL1 did not produce extracellular xylitol and produced more d-xylonate than the xyd1 strain containing the endogenous XYL1. K. lactis xyd1Δ XYL2 produced high concentrations of xylitol and significantly less d-xylonate than the xyd1 strain with the endogenous XYL2.
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