Effect of growth conditions on biosorption of cadmium and copper by yeast cells

Abstract

The dependence of Cd(II) and Cu(II) uptake by yeast cells on the age and temperature of cell culture was studied. Saccharomyces cerevisiae, Kluyveromyces marxianus and Debaromyces Hansenii were chosen as typical yeasts, while Cd(II) and Cu(II) as typical metal pollutants. Our results revealed that higher metal uptake was obtained by cells grown at the optimum temperature (30 oC) of cell culture. It was also found that the exponential phase cells resulted in a higher metal uptake than the stationary ones. A first interpretation of relevant bibliographic data concerning the effect of growth phase on metal uptake is proposed, assuming that limited qualitative changes in the cell wall structure take place as the cells pass from exponential to stationary phase, in addition to quantitative modifications, which have been reported in the literature. According to our interpretation the relative abundance among quantitative and qualitative alterations of cell wall, determines if stationary or exponential cells attain the higher metal binding capacity. An indication supporting our approach may be the fact that our hypothesis implies a decrease of pKa values of cell wall carboxyl groups with the age of cells, which is consistent with data reported by other authors.