S32: Genomic engineering strategies in industrial fuel ethanol Saccharomyces cerevisiae strains for efficient 1st and 2nd generation bioethanol production from sugarcane

In Brazil the production of fuel ethanol is based on the fermentation of sucrose from sugarcane, a mature and highly competitive technology. Taking into account that the feedstock costs have a major role in the overall economics of the process, it is expected that more efficient conversions of sucrose into ethanol (1^st generation bioethanol) will be of high economical significance. We have recently show that it is possible to improve sucrose fermentation through genomic and evolutionary engineering strategies that switch the way yeast cells ferment this disaccharide: the active transport and intracellular sucrose hydrolysis allows an increase of 11% in the ethanol yield. We have already introduced these modifications into the genome of diploid industrial fuel ethanol yeasts that dominate fermentation processes in Brazil, showing excellent results. Another promising strategy to improve bioethanol production is the fermentation of the lignocellulosic material present in sugarcane bagasse and leaves (2^nd generation bioethanol), a biomass containing large amounts of xylose. We have initially screen a panel of several Brazilian industrial S. cerevisiae strains for their ability to ferment xylulose (an intermediate in xylose catabolism), and the best xylulose fermenting yeasts were engineered by chromosomal integration of the xylose reductase, xylitol dehydrogenase and xylulokinase genes under control of strong constitutive promoters. Our results show that the transformed yeast strains can ferment xylose efficiently, especially under glucose-xylose or sucrose-xylose co-fermentations, highlighting the importance of modifying industrial yeast strains for efficient 1^st and 2^nd generation bioethanol production from sugarcane.