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 such
as high osmotic pressures, low nutrient availability or high ethanol levels. Given the broad
applications of yeast in the food industry, adaptation of yeast to stress conditions is an active
research area. It has been reported that membrane fluidity is affected temporarily or
permanently by environmental stresses (1-5), and thus, the regulation of the membrane
biophysical properties under such conditions may be a key point for yeast adaptation. In this
context, we here study the effect of ethanol stress on yeast membranes. We used the
laboratory strain Saccharomyces Cerevisiae (BY4741) wild type and also adapted to high
ethanol levels. We also included in the study a mutant with increased permeability due to the
lacks ergosterol (erg6Δ), and a commercial baker´s yeast, wich is not adapted to high ethanol
conditions. We used the probe Laurdan that has a fluorescent emission is sensitive to dipolar
relaxation 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 value
found 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%), GP
remained roughly constant, being the change of GP with CEtOH lower than 0.5%. At CEtOH
values higher than 20%, GP decreased abruptly. At these high ethanol levels, cell viability
decreased to cero, suggesting cells maintain the GP value while alive. In line with this, the GP
value of lipid liposomes or of death yeasts changed continuously with CEtOH.
We further studied BY4741 yeast adapted to high ethanol levels, and found similar behavior
than for WT BY4741 yeast: GP remained roughly constant at ethanol levels at which cells
were viable. However, the GP values for the adapted yeast was higher, values of 0.4 were
determined, 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 adapt
membrane composition in order to keep them with a certain order.
References:
1) Zhuang, S., Smart, K., & Powell, C. (2017). Impact of extracellular osmolality on Saccharomyces
yeast 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 relationships
between membrane fluidity and ethanol tolerance in Saccharomyces cerevisiae. World Journal of
Microbiology and Biotechnology, 33(12), 1-10.
3) Turk, M., Plemenita?, A., & Gunde-Cimerman, N. (2011). Extremophilic yeasts: plasma-membrane
fluidity as determinant of stress tolerance. Fungal biology, 115(10), 950-958.
4) Learmonth, R. P. (2011). Yeast membrane adaptation during fermentation. In Proceedings of the
2nd 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 membrane
polarization during mating in yeast cells. The Journal of cell biology, 173(6), 861-866.