Laboratory yeast strains fermenting mixtures of glucose and pentoses have been described earlier. However, those laboratory strains are extremely sensitive to toxic inhibitors and usually do not ferment properly in lignocellulosic hydrolysates. We have now used our newly discovered and patented xylose isomerase from Clostridium phytofermentans and an optimized arabinose-fermentation pathway together with specific pentose uptake systems to construct industrial yeast strains (Saccharomyces cerevisiae) efficiently fermenting the pentose sugars xylose and arabinose together with glucose in undetoxified plant biomass hydrolysates.

Compared to ethanol, the four carbon alcohol butanol shows superior properties as a potential biofuel. Therefore, we are engineering S. cerevisiae for the production of isobutanol instead of ethanol. Isobutanol production will finally be combined with pentose utilization.