title: Systematic strain construction and process development: Xylitol production by Saccharomyces cerevisiae expressing Candida tenuis xylose reductase in wild-type or mutant form.
abstract: A novel Saccharomyces cerevisiae whole-cell biocatalyst for xylitol production based on Candida tenuis xylose reductase (CtXR) is presented. Six recombinant strains expressing wild-type CtXR or an NADH-specific mutant were constructed and evaluated regarding effects of expression mode, promoter strength, biocatalyst concentration and medium composition. Intracellular XR activities ranged from 0.09 U mgProt(-1) to 1.05 U mgProt(-1) but did not correlate with the strains' xylitol productivities, indicating that other factors limited xylose conversion in the high-activity strains. The CtXR mutant decreased the biocatalyst's performance, suggesting use of the NADPH-preferring wild-type enzyme when (semi-)aerobic conditions are applied. In a bioreactor process, the best-performing strain converted 40 g L(-1) xylose with an initial productivity of 1.16 g L(-1)h(-1) and a xylitol yield of 100%. The obtained results underline the potential of CtXR wild-type for xylose reduction and point out parameters to improve "green" xylitol production.
authors.affiliation: Graz University of Technology, Institute of Biotechnology and Biochemical Engineering, NAWI Graz, Petersgasse 12, A-8010 Graz, Austria.
authors.forename: S M
authors.initials: SM
authors.lastname: Pratter
authors.affiliation: Graz University of Technology, Institute of Biotechnology and Biochemical Engineering, NAWI Graz, Petersgasse 12, A-8010 Graz, Austria.
authors.forename: T
authors.initials: T
authors.lastname: Eixelsberger
authors.affiliation: Graz University of Technology, Institute of Biotechnology and Biochemical Engineering, NAWI Graz, Petersgasse 12, A-8010 Graz, Austria. Electronic address: bernd.nidetzky@tugraz.at.
authors.forename: B
authors.initials: B
authors.lastname: Nidetzky
mesh_terms: D000449:Aldehyde Reductase / Q000378:metabolism*; D019149:Bioreactors; D002175:Candida / Q000201:enzymology / Q000235:genetics*; D005285:Fermentation; D005818:Genetic Engineering; D009249:NADP / Q000378:metabolism; D010957:Plasmids; D011401:Promoter Regions, Genetic; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D014993:Xylitol / Q000378:metabolism*; D014994:Xylose / Q000378:metabolism
chemical_list: D009249:NADP; D014994:Xylose; D000449:Aldehyde Reductase; D014993:Xylitol
keywords: Candida tenuis xylose reductase; Genetic engineering; Saccharomyces cerevisiae; Xylitol production