Final Activity Report Summary - DESYRE (Designed yeast for renewable bioethanol production) Lignocellulosic biomass, such as sustainable forestry and agricultural waste, contains large amounts of energy, stored in the form of sugars polymers such as cellulose and hemicellulose. Cellulose is composed of glucose, while hemicellulose is a polymer of different sugars, such as mannose, galactose, xylose and arabinose. Sugars can be converted to liquid biofuels, such as bioethanol, via fermentation. Bakers' yeast (Saccharomyces cerevisiae) is the prime choice for the production of bioethanol, since it converts most sugars to ethanol with high yield and productivity. However, yeast is unable to utilise xylose and arabinose, which account for a significant portion of lignocellulosic material. Thus, the objective of the work performed was to design new S. cerevisiae strains able to produce ethanol not only from the easily fermentable sugar glucose, but also from xylose and arabinose. Through metabolic engineering, new yeast strains were generated. The newly generated strains displayed different combinations of enzymes, forming the pathways through which xylose and arabinose could be introduced in yeast's metabolism and converted to ethanol. The strains were characterised in well-controlled bioreactors, so that the fermentation performance of each strain carrying different combination of enzymes could be thoroughly compared. In addition, new mutant enzymes, with improved characteristics for the expression in S. cerevisiae were tested. Finally, a combination of enzymes, encoded by genes from different organisms belonging to the kingdom of 'fungi' proved to be a promising solution for the development of new pentose fermenting strains.