Effect of ethanol on yeast membranes

D. GENOVESE; N. WILKE,

Conferencia; Online Molecular Membrane Biology Conference; 2021

Yeasts are able to support different environmental conditions, including stress situations suchas high osmotic pressures, low nutrient availability or high ethanol levels. Given the broadapplications of yeast in the food industry, adaptation of yeast to stress conditions is an activeresearch area. It has been reported that membrane fluidity is affected temporarily orpermanently by environmental stresses (1-5), and thus, the regulation of the membranebiophysical properties under such conditions may be a key point for yeast adaptation. In thiscontext, we here study the effect of ethanol stress on yeast membranes. We used thelaboratory strain Saccharomyces Cerevisiae (BY4741) wild type and also adapted to highethanol levels. We also included in the study a mutant with increased permeability due to thelacks ergosterol (erg6Δ), and a commercial baker´s yeast, wich is not adapted to high ethanolconditions. We used the probe Laurdan that has a fluorescent emission is sensitive to dipolarrelaxation arising from water penetration into the membrane. The Generalized Polarization(GP) was determined at increasing ethanol levels (CEtOH). GP of unstressed cells was 0.2-0.3 for all strains, indicating a high order such as that found in ternary mixtures of dipalmitoylglycero-phosphocholine/dioleoyl-glycero-phosphocholine/ergosterol (1:1:1). The similar valuefound in erg6Δ yeast suggest that the absence of ergosterol is buffered by other lipids,probably by its precursor Zymosterol. In the presence of low values of CEtOH (<20%), GPremained roughly constant, being the change of GP with CEtOH lower than 0.5%. At CEtOHvalues higher than 20%, GP decreased abruptly. At these high ethanol levels, cell viabilitydecreased to cero, suggesting cells maintain the GP value while alive. In line with this, the GPvalue of lipid liposomes or of death yeasts changed continuously with CEtOH.We further studied BY4741 yeast adapted to high ethanol levels, and found similar behaviorthan for WT BY4741 yeast: GP remained roughly constant at ethanol levels at which cellswere viable. However, the GP values for the adapted yeast was higher, values of 0.4 weredetermined, indicating an increase in the membrane order for the adapted yeasts.We conclude that maintaining a GP value is crucial for cell viability, and that cells adaptmembrane composition in order to keep them with a certain order.References:1) Zhuang, S., Smart, K., & Powell, C. (2017). Impact of extracellular osmolality on Saccharomycesyeast populations during brewing fermentations. Journal of the American Society of Brewing Chemists,75(3), 244-254.2) Ishmayana, S., Kennedy, U. J., & Learmonth, R. P. (2017). Further investigation of relationshipsbetween membrane fluidity and ethanol tolerance in Saccharomyces cerevisiae. World Journal ofMicrobiology and Biotechnology, 33(12), 1-10.3) Turk, M., Plemenita?, A., & Gunde-Cimerman, N. (2011). Extremophilic yeasts: plasma-membranefluidity as determinant of stress tolerance. Fungal biology, 115(10), 950-958.4) Learmonth, R. P. (2011). Yeast membrane adaptation during fermentation. In Proceedings of the2nd International Seminar on Chemistry: Chemestry for a Better Future (ISC 2011) (pp. 431-440).Padjadjaran University.5) Proszynski, T. J., Klemm, R., Bagnat, M., Gaus, K., & Simons, K. (2006). Plasma membranepolarization during mating in yeast cells. The Journal of cell biology, 173(6), 861-866.