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

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.