8-06: Intracellular redox state as key target for Saccharomyces cerevisiae tolerance to lignocellulosic hydrolysate inhibitors

Liberation of sugars monomers from the polysaccharides constituting lignocellulosic biomass requires pretreatment and hydrolysis. Harsh conditions during pretreatment promote the formation of a number of inhibitory compounds, among which the furaldehydes furfural and hydroxymethylfurfural (HMF) have shown to impede growth and limit ethanol productivity of the yeast Saccharomyces cerevisiae. Cellular damage response to such inhibitory molecules and repair come at an energy cost for the cell, which could be reflected by alterations in energy and redox metabolism.

In this study, S. cerevisiae cultures where treated with sub-lethal concentrations of furfural and HMF, both in continuous and batch cultivations. In continuous cultures, the inhibitors concentration was as close as possible to lethal, yet allowing steady state. In batch cultivations, the chosen concentration completely inhibited growth, yet allowing growth resumption. Metabolites connected to energy and redox metabolism such as NAD(P)H, NADP⁺, ATP, ADP and AMP were quantified and transcriptome analysis was performed. The results, along with data from thorough physiological characterisation under the studied conditions, suggested a severe impact of furfural and HMF on energy and redox metabolism. Based on this evidence, new strain with altered redox carriers intracellular concentration were engineered. The new recombinant strains showed higher ethanol productivity in the presence of lignocellulosic hydrolysate inhibitors.