Influence of Cell Surface and Nanomechanical Properties on the Flocculation Ability of Industrial Saccharomyces cerevisiae Strains

Abstract

In the past few years, atomic force microscopy (AFM) has provided novel information on the ultrastructural and nanomechanical properties of yeast cell walls that play a major role in determining the flocculation characteristics of the yeasts. In this study, we used AFM to visualize at the nanoscale the cell surface topography and to determine cell wall nanomechanical properties (e.g. elasticity and adhesion) of different strains of S. cerevisiae employed for brewing, winemaking and fuel alcohol production. Cell surface topography was found to correlate with the flocculation behaviour of these strains during their late stationary phase, with the cell surface of flocculent cells being rougher than that of weakly flocculent cells. The elastic modulus of the yeast cell walls showed that weakly flocculent strains had a more rigid cell wall than highly flocculent strains. This difference in elasticity seemed to have an effect on the adhesive properties of the yeast cell walls, with weakly flocculent yeasts displaying lower adhesion energy than the highly flocculent strains. These findings seem to indicate that yeast cell surface nanomechanical properties play an important role in governing flocculation.

Stiffness of brewers’ yeast under ethanol stress investigated by atomic force microscopy

“…The average stiffness of brewers' yeasts is the order of 10 5 -10 6 Pa, which has been observed in previous AFM studies 8,11,12,15,31,32) and is much higher than animal cells. [17][18][19] Thus it has been considered that E of yeast cells measured by AFM mainly reflects the stiffness of cell wall that supports yeast cell morphology.…”

“…However, it is still unclear how the temporal variation in ethanol stress occurring during beer brewing influences the mechanical strength of brewers' yeast cells. Here, we investigated the effect of variation in ethanol concentration, C EtOH , on the mechanical strength of brewers' yeast cells by atomic force microscopy (AFM), which is a useful technique for quantifying the mechanical property of not only yeast cells [8][9][10][11][12][13][14][15][16] but also animal cells [17][18][19] at the single cell level. We found with a quantitative assessment of cell viability that brewers' yeast cells acquired ethanol tolerance as C EtOH was gradually increased toward a critical value for a few days while a significant reduction of survival rate was appeared as C EtOH was abruptly changed into the critical value.…”