The change in the electro-rotation of yeast cells effected by silver ions

Abstract

Pre-treatment of brewer's yeast ( Saccharomyces cerevisiae) cells with silver acetate or nitrate at concentrations of 20 nmol/l or higher caused a dramatic increase in the number of cells which rotated in the same direction as the field (‘Co-field rotation’). The change in rotation of single cells correlated very well with the chemically observed loss of potassium induced by Ag +. The sensitivity to Ag + was lowered by increasing the cell concentration, and the extent of this change can be used to estimate the binding of Ag + per cell and the limiting sensitivity of the method. The Ag + concentration required to induce a response was found to be increased significantly in the presence of alkali ions (especially K +) during the Ag + incubation. The Ag + sensitivity was, therefore, observed to be a function of the type and strength of buffer used in the incubation. Under certain conditions, 1 mM Ca 2+ increased the Ag + sensitivity. These observations show that the presence or absence of ions that are so common that they are often overlooked may have interesting consequences for the bio-assay of heavy metals.