title: Effect of enhanced xylose reductase activity on xylose consumption and product distribution in xylose-fermenting recombinant Saccharomyces cerevisiae.
abstract: Recombinant Saccharomyces cerevisiae TMB3001, harboring the Pichia stipitis genes XYL1 and XYL2 (xylose reductase and xylitol dehydrogenase, respectively) and the endogenous XKS1(xylulokinase), can convert xylose to ethanol. About 30% of the consumed xylose, however, is excreted as xylitol. Enhanced ethanol yield has previously been achieved by disrupting the ZWF1 gene, encoding glucose-6-phosphate dehydrogenase, but at the expense of the xylose consumption. This is probably the result of reduced NADPH-mediated xylose reduction. In the present study, we increased the xylose reductase (XR) activity 4-19 times in both TMB3001 and the ZWF1-disrupted strain TMB3255. The xylose consumption rate increased by 70% in TMB3001 under oxygen-limited conditions. In the ZWF1-disrupted background, the increase in XR activity fully restored the xylose consumption rate. Maximal specific growth rates on glucose were lower in the ZWF1-disrupted strains, and the increased XR activity also negatively affected the growth rate in these strains. Addition of methionine resulted in 70% and 50% enhanced maximal specific growth rates for TMB3255 (zwfl Delta) and TMB3261 (PGK1-XYL1, zwf1 Delta), respectively. Enhanced XR activity did not have any negative effect on the maximal specific growth rate in the control strain. Enhanced glycerol yields were observed in the high-XR-activity strains. These are suggested to result from the observed reductase activity of the purified XR for dihydroxyacetone phosphate.
authors.affiliation: Department of Applied Microbiology, Lund University, P.O. Box 124, 221 00 Lund, Sweden.
authors.forename: Marie
authors.initials: M
authors.lastname: Jeppsson
authors.forename: Karin
authors.initials: K
authors.lastname: Träff
authors.forename: Björn
authors.initials: B
authors.lastname: Johansson
authors.forename: Bärbel
authors.initials: B
authors.lastname: Hahn-Hägerdal
authors.forename: Marie F
authors.initials: MF
authors.lastname: Gorwa-Grauslund
mesh_terms: D000449:Aldehyde Reductase / Q000378:metabolism*; D004271:DNA, Fungal / Q000737:chemistry / Q000235:genetics; D000431:Ethanol / Q000378:metabolism; D005285:Fermentation; D007700:Kinetics; D010843:Pichia / Q000737:chemistry / Q000235:genetics; D011994:Recombinant Proteins; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D014170:Transformation, Genetic; D014993:Xylitol / Q000378:metabolism; D014994:Xylose / Q000378:metabolism*
chemical_list: D004271:DNA, Fungal; D011994:Recombinant Proteins; D000431:Ethanol; D014994:Xylose; D000449:Aldehyde Reductase; D014993:Xylitol