Evaluating the adhesion force between Saccharomyces cerevisiae yeast cells and polystyrene from shear-flow induced detachment experiments

The present paper focused on the quantification of the adhesion force between Saccharomyces cerevisiae yeast cells and polystyrene, using laboratory and industrial yeast strains, in a suspending medium of high ionic strength (150 mM NaCl). To this end, shear-flow induced detachment experiments, performed in a flow chamber, were combined with a simplified version of a theoretical model, based on the balance of hydrodynamic forces and torque exerted over yeast cells. It was assumed that yeast adhesion to solid surfaces is mediated by surface proteins and a characteristic thickness of the protein meshwork was thus introduced (25.0 +/- 2.5 nm). The experimental determination of the wall shear stress required to remove 50% of the cells initially adherent to polystyrene allowed the estimation of the adhesion force. On this basis, adhesion forces of 6 +/- 2 nN and 11 +/- 8 nN were obtained for laboratory and industrial strains respectively, reflecting the non-specific interactions, such as Lifshitz-van der Waals and Lewis acid/base interactions, between yeast cells and the polymeric surface. The force magnitude was in the experimental range reported in the literature (between 1 and 50 nN), for a wide variety of solid surfaces and bacterial or fungal species. The mechanism for yeast detachment was established (mainly rolling). The flow chamber and the associated theoretical modelling were thus demonstrated to be a relevant approach to quantify physico-chemical interactions between biological and physical surfaces.