Development of Next Generation Yeast Strains for Ethanol Production from Lignocellulosic Feedstocks

Lignocellulosic feedstocks are considered to be of great economic and environmental significance for sustainable production of valuable fermentation products. For cost- effective and efficient industrial processes, complete and fast fermentation of all biomass sugars is a prerequisite. In this respect, the main challenge emerging from the use of lignocellulosic feedstocks for ethanol production by Saccharomyces cerevisiae is the efficient fermentation of the pentose sugars xylose and arabinose, as these sugars cannot be utilized by natural S. cerevisiae strains. Another significant challenge is the inevitable presence of inhibitors, such as furfural and acetic acid, which are formed during pretreatment and hydrolysis of the feedstocks and severely inhibit yeast growth and product formation.
DSM has developed advanced yeast strains by introducing heterologous pathways into robust S. cerevisiae hosts which resulted in the ability to ferment xylose and arabinose in lignocellulosic hydrolysates. Subsequently, by the application of evolutionary engineering the total time required to ferment hexoses and pentoses in lignocellulosic sugar mixtures was significantly reduced.
In order to take these developments to the next level, a toolbox for the new generation of advanced yeast strains is in development, in which the main challenges are further addressed by accelerating pentose fermentation through expression of engineered pentose transporters, as well as converting lignocellulosic inhibitors and biorefinery waste streams into additional ethanol. A first glance at these new developments will be presented.