Physiological analysis of Saccharomyces cerevisiae cells exposed to furfural, an important fermentation inhibitor

Saccharomyces cerevisiae is the preferred microorganism in the ethanol fermentation industry. However its use for the fermentation of renewable resources such as lignocellulosic biomass is impaired by several metabolic bottlenecks and toxic by-products formed in the pre-treatment process. Furfural is the most abundant by-product of hemicellulose hydrolysis which inhibits yeast growth [1]. At low concentrations, S. cerevisiae can overcome furfural toxicity by converting it to the corresponding alcohol (furfuryl alcohol) by NAD(P)H-dependent reactions [2]. Unfortunately these mechanisms of detoxification compete for key enzymes and cofactors needed to branch carbon flow to respiration and to ethanol production. Several studies have reported that furfural at high concentrations decreases yeast viability, specific growth rate and volumetric fermentation rate. Recently it has been proposed that furfural induces reactive oxygen species (ROS) generation and cellular damage in S. cerevisiae (3) ever the mechanism of furfural toxicity in yeast is not yet fully understood. We have carried out a flow cytometry analysis of yeast CEN-PK cells in the presence of different concentrations of furfural. We did not observe any significant increase of ROS production even at concentrations that abolished growth. However, we found that furfural induced a strong membrane depolarization during the lag phase, followed by hyperpolarization and cell death after the cells had started growing. Our results shed light on the mechanisms of toxicity of furfural in yeast and pave the way to a rational approach to improvement of tolerance of S. cerevisiae