17-43: Industrial C5/C6 Saccharomyces cerevisiae strains for efficient fermentation of lignocellulosic feedstock

Lignocellulose raw materials are composed of lignin, cellulose and hemicellulose and require pre-treatment at elevated temperatures with acid or base to make cellulose and hemicellulose accessible to subsequent acid or enzymatic hydrolysis. Cellulose and hemicellulose are hydrolyzed to fermentable monomer C6 and C5 sugars (glucose, mannose, galactose, xylose and arabinose), while lignin may be recovered for  fuel and chemical production. During pre-treatment and hydrolysis fermentation inhibitors – phenol and furan derivatives and low molecular weight fatty acids - are also released. Hydrolyzed lignocellulose raw materials thus comprise a mixed-sugar substrate in an inhibiting matrix. The yeast Saccharomyces cerevisiae is currently the prime choice for industrial ethanol production due to its tolerance to inhibitors and its ease of use.

While S. cerevisiae  readily ferments C6 sugars, genetic engineering is required for construction of strains that can effectively consume also the C5 sugars xylose and arabinose. Various metabolic engineering strategies as well as random methods such as breeding, adaptation/evolutionary engineering and mutagenesis are generally used to produce such strains. We have used rational genetic engineering strategies to generate novel C5-fermenting industrial S. cerevisiae  strains. The fermentation performance of these strains  in  lignocellulose hydrolysates will be presented. Strains with improved utilization of pentose (C5) sugars and improved inhibitor tolerance will  be exploited in the future biofuels and biorefinery industries based on renewable lignocellulose raw materials.