S103: Application of evolutionary engineering strategies for improving the C5-sugars utilization by engineered Saccharomyces cerevisiae strains for bioethanol production from lignocellulosic feedstocks

The use of evolutionary engineering has proven to be very valuable for obtaining phenotypes of industrial microorganisms with improved properties, such as expanded substrate range, increased stress tolerance and efficient substrate utilization. Also, for the yeast Saccharomyces cerevisiae, the preferred organism for large-scale bioethanol production from lignocellulosic feedstocks, evolutionary engineering has been extensively used to select for industrially relevant phenotypes. For ethanol production from lignocellulosic feedstocks by S. cerevisiae, one of the main challenges is the efficient conversion of the pentoses (xylose and arabinose) to ethanol, especially in the presence of inhibitors. DSM has developed industrial advanced yeast strains that have been genetically engineered to enable the conversion of the pentose sugars to ethanol, retaining at the same time the ability to ferment rapidly hexoses. Evolutionary engineering techniques are part of the DSM R&D toolbox, aiming at continuous improvement of industrial advanced yeast strains contributing in this way to the development of cost-effective, sustainable and efficient processes for bioethanol production. This paper describes the work aiming at further improvement of the conversion rates of C5-sugars in such strains by applying adaptive evolution approaches, such as sequential batch reactor (SBR) and chemostat cultivations. The fermentation kinetics of C6- and C5-sugars in synthetic media as well as in lignocellulosic hydrolysates, at an economically relevant dry matter level, will be presented.