Poster Presentation 2-12
d-Xylose Transport by Candida succiphila and Kluyveromyces marxianus
Boris U. Stambuk2, Mary Ann Franden1, Arjun Singh1, and Min Zhang1
1National Renewable Energy Laboratory 1617 Cole Blvd. Golden, CO, 80401
2Departamento de Bioquímica, UFSC Florianópolis, SC, Brazil
E-mail: bstambuk@mbox1.ufsc.br
Fermentation of the pentose sugar d‑xylose into ethanol is essential for an economically feasible production of fuel ethanol from plant biomass. Since the preferred organism in industrial ethanol fermentation processes is the yeast Saccharomyces cerevisiae (a microorganism unable to utilize xylose), several laboratories have attempted to engineer this yeast for efficient xylose fermentation. Although the results of such genetically engineered yeasts have been encouraging, it was recently shown that xylose uptake limits the xylose flux and metabolism by these recombinant strains. We have characterized the xylose transport system(s) in the yeasts C. succiphila and K. marxianus. C. succiphila is one of the few yeasts capable of fermenting both d‑xylose and l‑arabinose under microaerobic conditions. This yeast showed a high affinity and active xylose transport activity when grown on xylose, while after growth on glucose the cells transported xylose by a facilitated diffusion activity with low affinity for the substrate. Sugar competition studies indicated that the high affinity system is probably mediated by a general monosaccharide transporter, while the low affinity system occurs through glucose transporters. A very different pattern was found with K. marxianus that utilizes pentoses without significant ethanol production. We will report in more detail in this presentation.
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