<p>Abstract</p> <p>Background</p> <p>Hydrolysates of plant biomass used for the production of lignocellulosic biofuels typically contain sugar mixtures consisting mainly of D-glucose and D-xylose, and minor amounts of L-arabinose. The yeast <it>Saccharomyces cerevisiae </it>is the preferred microorganism for the fermentative production of ethanol but is not able to ferment pentose sugars. Although D-xylose and L-arabinose fermenting <it>S. cerevisiae </it>strains have been constructed recently, pentose uptake is still a limiting step in mixed sugar fermentations.</p> <p>Results</p> <p>Here we described the cloning and characterization of two sugar transporters, AraT from the yeast <it>Scheffersomyces stipitis </it>and Stp2 from the plant <it>Arabidopsis thaliana</it>, which mediate the uptake of L-arabinose but not of D-glucose into <it>S. cerevisiae </it>cells. A yeast strain lacking all of its endogenous hexose transporter genes and expressing a bacterial L-arabinose utilization pathway could no longer take up and grow with L-arabinose as the only carbon source. Expression of the heterologous transporters supported uptake and utilization of L-arabinose especially at low L-arabinose concentrations but did not, or only very weakly, support D-glucose uptake and utilization. In contrast, the <it>S. cerevisiae </it>D-galactose transporter, Gal2, mediated uptake of both L-arabinose and D-glucose, especially at high concentrations.</p> <p>Conclusions</p> <p>Using a newly developed screening system we have identified two heterologous sugar transporters from a yeast and a plant which can support uptake and utilization of L-arabinose in L-arabinose fermenting <it>S. cerevisiae </it>cells, especially at low L-arabinose concentrations.</p
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