The effect of lignocellulosic biomass pretreatment by-products on the fermentation activity of Saccharomyces cerevisiae yeast, measured using indices of toxic stress

The use of lignocellulosic biomass as a renewable raw material for the production of cellulosic ethanol requires pretreatment. Unfortunately, this process can generate numerous by-products that have a toxic effect on yeasts. Understanding the response of yeast is crucial if measures are to be developed that allow adaptation under multifactorial stress conditions. The study objective was to determine the effect that inhibitors in the form of by-products of lignocellulose pretreatment have on yeast fermentation activity. The yeast Saccharomyces cerevisiae was fermented in liquid media containing, at three dose concentrations in each case, 5-hydroxymethylfurfural or furfural or vanillin or a combination of all three fermentation inhibitors. Yeast biomass growth; glucose consumption and ethanol formation; malondialdehyde concentration; superoxide dismutase, glutathione peroxidase and catalase activity; and HSP70 and HSP104 protein expression were analyzed. The introduction of fermentation inhibitors to the medium resulted in changes in concentration of yeast biomass and in ethanol produced. In particular, numerous fluctuations were observed in the analyzed markers in response to exposure to the combination of inhibitors, especially at medium and high doses of 5-hydroxymethylfurfural, furfural and vanillin. The highest doses of inhibitors increased malondialdehyde concentration, superoxide dismutase and glutathione peroxidase activity. In turn, the expression of HSP proteins in yeast exposed to various concentrations of by-products was increased in almost all variants. Thus, although exposure to single inhibitors did not reveal a toxic effect on yeast even at the highest concentrations, there was a synergistic effect for toxic stress resulting from the combined effect of the tested inhibitors.