Comparison of the xylose reductase-xylitol dehydrogenase and the xylose isomerase pathways for xylos.pdfVIP

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Comparison of the xylose reductase-xylitol dehydrogenase and the xylose isomerase pathways for xylos.pdf

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Comparison of the xylose reductase-xylitol dehydrogenase and the xylose isomerase pathways for xylos

BioMed CentralMicrobial Cell Factories ssOpen AcceResearch Comparison of the xylose reductase-xylitol dehydrogenase and the xylose isomerase pathways for xylose fermentation by recombinant Saccharomyces cerevisiae Kaisa Karhumaa, Rosa Garcia Sanchez, B?rbel Hahn-H?gerdal and Marie- F Gorwa-Grauslund* Address: Department of Applied Microbiology, Lund University, P.O.Box 124, SE-22100 Lund, Sweden Email: Kaisa Karhumaa - kaisa.karhumaa@tmb.lth.se; Rosa Garcia Sanchez - Rosa.Garcia_Sanchez@tmb.lth.se; B?rbel Hahn- H?gerdal - Barbel.Hahn-Hagerdal@tmb.lth.se; Marie-F Gorwa-Grauslund* - Marie-Francoise.Gorwa@tmb.lth.se * Corresponding author Abstract Background: Two heterologous pathways have been used to construct recombinant xylose- fermenting Saccharomyces cerevisiae strains: i) the xylose reductase (XR) and xylitol dehydrogenase (XDH) pathway and ii) the xylose isomerase (XI) pathway. In the present study, the Pichia stipitis XR-XDH pathway and the Piromyces XI pathway were compared in an isogenic strain background, using a laboratory host strain with genetic modifications known to improve xylose fermentation (overexpressed xylulokinase, overexpressed non-oxidative pentose phosphate pathway and deletion of the aldose reductase gene GRE3). The two isogenic strains and the industrial xylose- fermenting strain TMB 3400 were studied regarding their xylose fermentation capacity in defined mineral medium and in undetoxified lignocellulosic hydrolysate. Results: In defined mineral medium, the xylose consumption rate, the specific ethanol productivity, and the final ethanol concentration were significantly higher in the XR- and XDH- carrying strain, whereas the highest ethanol yield was achieved with the strain carrying XI. While the laboratory strains only fermented a minor fraction of glucose in the undetoxified lignocellulose hydrolysate, the industrial strain TMB 3400 fermented nearly all the sugar available. Xylitol was formed by the XR-XDH-carrying strains only in