Application of adaptive evolution for improving next generation Saccharomyces cerevisiae strains towards a more efficient cellulosic ethanol production

In the past decades, it has become clear that utilization of lignocellulosic biomass is a sustainable and cost-effective option for biofuels production. Key to economic viability is cheap production and application of different enzymes in order to hydrolyze the lignocellulosic carbohydrates into fermentable sugars, and subsequently convert the sugars into specific products at high productivities and yields.

DSM has developed industrially robust advanced yeast strains that have been genetically engineered to enable fermentation of biomass derived sugars into ethanol. Due to the toxic nature of the hydrolysates, fermentation can be slow and/or incomplete. Especially, the efficient and fast conversion of pentose sugars into ethanol, in the presence of inhibitors, is often the main challenge. Recently, we have been focusing on developing next generation yeast strains by accelerating pentose fermentation through engineered pentose transport, as well as converting lignocellulosic inhibitors into additional ethanol. Adaptive evolution, i.e. cultivating a microorganism under clearly defined conditions for prolonged periods of time combined with mutagenesis, screening and selection, is a powerful method for generating novel desired phenotypes and part of the DSM R&D toolbox.

This paper describes the work on improving the pentoses’ consumption rates and the tolerance towards inhibitors in next generation S. cerevisiae strains by applying adaptive evolution approaches. Those include sequential batch and fed-batch or chemostat cultivations, under selective conditions in the presence of synthetic media or hydrolysates. The improved ethanol fermentation kinetics in lignocellulosic hydrolysates, at an economically relevant dry matter content, will be presented.

© 2015 DSM. All rights reserved