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±2g d-xylonatel ^-1 was produced when K. lactis expressing xyd1 was grown on 10.5gd-galactosel ^-1 and 40g d-xylosel ^-1. Intracellular accumulation of d-xylonate (up to ~70mg [gbiomass] ^-1) was observed.d-Xylose was metabolised to d-xylonate, xylitol and biomass. Oxygen could be reduced to 6mmolO ₂l ^-1h ^-1 without loss in titre or production rate, but metabolism of d-xylose and xylitol were more efficient when 12mmolO ₂l ^-1h ^-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.