title: Saccharomyces cerevisiae engineered to produce D-xylonate.
abstract: Saccharomyces cerevisiae was engineered to produce D-xylonate by introducing the Trichoderma reesei xyd1 gene, encoding a D-xylose dehydrogenase. D-xylonate was not toxic to S. cerevisiae, and the cells were able to export D-xylonate produced in the cytoplasm to the supernatant. Up to 3.8 g of D-xylonate per litre, at rates of 25-36 mg of D-xylonate per litre per hour, was produced. Up to 4.8 g of xylitol per litre was also produced. The yield of D-xylonate from D-xylose was approximately 0.4 g of D-xylonate per gramme of D-xylose consumed. Deletion of the aldose reductase encoding gene GRE3 in S. cerevisiae strains expressing xyd1 reduced xylitol production by 67%, increasing the yield of D-xylonate from D-xylose. However, D-xylose uptake was reduced compared to strains containing GRE3, and the total amount of D-xylonate produced was reduced. To determine whether the co-factor NADP+ was limiting for D-xylonate production the Escherichia coli transhydrogenase encoded by udhA, the Bacillus subtilis glyceraldehyde 3-phosphate dehydrogenase encoded by gapB or the S. cerevisiae glutamate dehydrogenase encoded by GDH2 was co-expressed with xyd1 in the parent and GRE3 deficient strains. Although each of these enzymes enhanced NADPH consumption on D-glucose, they did not enhance D-xylonate production, suggesting that NADP+ was not the main limitation in the current D-xylonate producing strains.
authors.affiliation: VTT, Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT Espoo, Finland. mervi.toivari@vtt.fi
authors.forename: Mervi H
authors.initials: MH
authors.lastname: Toivari
authors.forename: Laura
authors.initials: L
authors.lastname: Ruohonen
authors.forename: Peter
authors.initials: P
authors.lastname: Richard
authors.forename: Merja
authors.initials: M
authors.lastname: Penttilä
authors.forename: Marilyn G
authors.initials: MG
authors.lastname: Wiebe
mesh_terms: D000429:Alcohol Oxidoreductases / Q000378:metabolism*; D005800:Genes, Fungal; D005818:Genetic Engineering / Q000379:methods*; D005956:Glucose-6-Phosphate Isomerase / Q000378:metabolism; D005986:Glyceraldehyde 3-Phosphate / Q000378:metabolism; D009249:NADP / Q000378:metabolism*; D010084:Oxidation-Reduction; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D013400:Sugar Acids / Q000378:metabolism*; D014242:Trichoderma / Q000201:enzymology / Q000235:genetics; D014994:Xylose / Q000378:metabolism
chemical_list: D013400:Sugar Acids; D005986:Glyceraldehyde 3-Phosphate; D009249:NADP; D014994:Xylose; D000429:Alcohol Oxidoreductases; C035795:D-xylose dehydrogenase; D005956:Glucose-6-Phosphate Isomerase