Abstract
Understanding the specific response of yeast cells to environmental stress factors is the starting point for selecting the conditions of adaptive culture in order to obtain a yeast line with increased resistance to a given stress factor. The aim of the study was to evaluate the specific cellular response of Saccharomyces cerevisiae strain Ethanol Red to stress caused by toxic by-products generated during the pretreatment of lignocellulose, such as levulinic acid, 5-hydroxymethylfurfural, furfural, ferulic acid, syringaldehyde and vanillin. The presence of 5-hydroxymethylfurfural at the highest analyzed concentration (5704.8 ± 249.3 mg/L) under aerobic conditions induced the overproduction of ergosterol and trehalose. On the other hand, under anaerobic conditions (during the alcoholic fermentation), a decrease in the biosynthesis of these environmental stress indicators was observed. The tested yeast strain was able to completely metabolize 5-hydroxymethylfurfural, furfural, syringaldehyde and vanillin, both under aerobic and anaerobic conditions. Yeast cells reacted to the presence of furan aldehydes by overproducing Hsp60 involved in the control of intracellular protein folding. The results may be helpful in optimizing the process parameters of second-generation ethanol production, in order to reduce the formation and toxic effects of fermentation inhibitors.
Highlights
Bioethanol produced from lignocellulose is an alternative to fossil fuels and other energy sources, and its production from waste materials and energy crops does not pose a risk of rising food and feed prices
We analyzed the specific cellular response of the S. cerevisiae strain Ethanol Red to the toxic stress caused by the presence of inhibitors in the culture medium, which are formed as by-products during the pretreatment of lignocellulosic biomass
Our studies showed that vanillin at the analyzed concentrations had no effect on the concentration of ergosterol in yeast cells
Summary
Bioethanol produced from lignocellulose is an alternative to fossil fuels and other energy sources, and its production from waste materials and energy crops does not pose a risk of rising food and feed prices. Due to the complex structure of lignocellulosic biomass, composed of cellulose, hemicellulose and lignins, pretreatment is a necessary step before enzymatic hydrolysis and fermentation. The aim of pretreatment is to increase the susceptibility of biomass to enzymatic hydrolysis, by reducing the number of crystalline regions in cellulose, and partial degradation of hemicellulose and lignins [1,2]. Under the influence of the factors used, toxic by-products can be formed These compounds are classified into three groups: weak organic acids (acetic, formic and levulinic acid), furan compounds (5-hydroxymethylfurfural, furfural) and phenolic compounds (syringaldehyde, ferulic acid, vanillin, 4-hydroxybenzoic acid). These compounds are considered inhibitors of yeast metabolism. Vanillin and vanillic acid are degradation products of guaiacylpropane units of lignin [4,5,6,7,8,9]
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