Flocculation-Some Observations on the Surface Charges of Yeast Cells

Surface charges on flocculent and non-flocculent yeast cells have been measured by micro-electrophoresis. Yeasts were grown both in calcium deficient and in complete medium and particular attention was paid to changes as cells passed from a logarithimic to a stationary phase of growth. Many of the ionogenic groups contributing to surface charge are situated well within the cell wall; charges on cells from the calcium-deficient medium were higher than on cells from the complete medium. A pH-dependent rearrangement of an underlying surface protein layer is postulated for the flocculent yeast Saccharomyces cerevisiae Strain NCYC 1109. No evidence of a similar rearrangement was found with other flocculent strains examined. The results are discussed in relation to ‘calcium bridge’ formation.