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 o C) 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 pK a values of cell wall carboxyl groups with the age of cells, which is consistent with data reported by other authors. KEYWORDS: uptake, removal, Saccharomyces cerevisiae, Kluyveromyces marxianus, Debaromyces Hansenii, growth phase, growth temperature. INTRODUCTIONWater pollution, due to heavy metals, is a serious worldwide problem. Cadmium is a heavy metal, which poses serious health hazards through entry into the food chain (Vasudevan et al., 2003). Copper is another heavy metal with many industrial applications (Konstantinou and Pashalidis, 2008). Although it is an essential element, WHO has established a limit of 2 mg L -1 as the maximum acceptable concentration in drinking water. Aiming at removal of heavy metals, numerous attempts have been made to treat wastewaters by traditional methods such as, chemical precipitation, lime coagulation, ion-exchange, reverse osmosis, membrane separation, adsorption onto active carbon, e.t.c. However, all these methods have shown varying performances, often incomplete metal removal, especially in low concentration pollutant range, high energy requirements, high capital investment and operating costs (Grimm et al., 2008;Vázquez et al., 2009;Chojnacka and Michalak, 2009).