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

Ashima Nayyar,Ashok K Adya,Elisabetta Canetta,Forbes Wardrop,Graeme Walker

doi:10.5539/jfr.v6n5p1

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.

Highlights

The yeast cell wall is a complex carbohydrate membrane, which protects the yeast cells from adverse conditions and helps maintain an optimum osmotic balance to ensure normal cellular activities
We used atomic force microscopy (AFM) to visualize at the nanoscale the cell surface topography and to determine cell wall nanomechanical properties 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

Summary

Introduction

The yeast cell wall is a complex carbohydrate membrane, which protects the yeast cells from adverse conditions and helps maintain an optimum osmotic balance to ensure normal cellular activities. The first class comprises of the proteins that are bound non covalently to the β-1,3- glucan network (the SCWs family); the second category consists of proteins attached covalently through a remnant of the GPI anchor to β-1,6-glucans (the GPI-CWPs); and the third class is made of cell wall mannoproteins that are characterized by Protein Internal Repeat regions (PIR-CWPs or CCWs family) that are directly linked to β-1,3- glucans (Klis, Boorsma & de Groot , 2006) This outer layer is made of highly mannosylated proteins together with large polysaccahrides complex of 150 or more D-mannose units. The mannoprotein layer bears crucial biochemical and biotechnological properties, some of which are adhesion, aggregation and flocculation (Caridi, 2006; Verstrepen & Klis, 2006) as well as virulence

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