Discovery of novel pathways to develop inhibitor tolerant yeast Saccharomyces cerevisiae to hot-compressed water-treated cellulose hydrolysate

Inhibitory compounds present in hot-compressed water-treated lignocelluloses hydrolysate (HCWT-lig. Hyd.) hamper the growth and ethanol fermentation of yeast Saccharomyces cerevisiae, and one of the key barrier for industrialization of this advanced biomass pre-treatment technology. We have identified glycolaldehyde is the strongest inhibitor present in HCWT-lig. Hyd.¹ and developed a tolerant yeast strain by overexpressing oxidoreductases^{2, 3}. However, the developed strain still struggles to overcome the combinational inhibitory effect of HCWT-lig. Hyd.. We carried out a comprehensive genomic study for insight into the molecular mechanism of tolerance of combinational inhibitory effect of HCWT-lig. Hyd.¹. We identified 68 mutants as those specifically involved in tolerance of yeast in HCWT-lig. Hyd.. Examining outliers of PCA result of inhibitory profile of these mutants, we identified sumolysation as a potential mechanism to overcome combinational inhibitor effect of HCWT-lig. Hyd.¹. Indeed, overexpression of SUMO-protein producing-SMT3 in yeast significantly improves the growth and ethanol fermentation of yeast in the combinational inhibitory medium. Best of our knowledge, this is the first successful use of sumolysation pathway for engineering yeast strain for inhibitor tolerance. In sum, our study established novel knowledge and rational platform to engineering yeast strain tolerant to lignocelluloses hydrolysate, and benefit to overcome one of the critical barrier for commercialization of lignocellulosic ethanol production. 

Ref;  1. Jayakody et al., Biotechnol. Let., 33, 285-289 (2011)
2. Jayakody et al., Appl. Microbiol. Biotechnol., 94, 273-283 (2012)*
3. Jayakody et al., Appl. Microbiol. Biotechnol., 97, 6589-6600 (2013)
*Key Scientific Article, Renewable Energy Global Innovations