Toxic effects caused by heavy metals in the yeast Saccharomyces cerevisiae:: a comparative study

The decreasing order of toxicity of select heavy metals on the yeast Saccharomyces cerevisiae, in 10 mM MES (2-(N-morpholino)ethanesulfonic acid) pH buffer at pH 6.0, was found to be copper, lead, and nickel. Heavy metal (200 muM) induced a decrease in the number of viable cells by about 50% in the first 5 min for copper and in 4 h for lead, while nickel was not toxic up to a 200 muM concentration over a period of 48 h. Glucose (25 mM) strongly enhanced the toxic effect of 50 muM copper but had little or no effect on the toxicity of 200 muM lead or nickel. Copper, lead, and nickel induced the leakage of UV260-absorbing compounds from cells with different kinetics. The addition of 0.5 mM calcium, before addition of 200 muM copper, showed a protective action against cell death and decreased the release of UV-absorbing compounds, while no effect was observed against lead or nickel toxic effects. Copper complexation capacities of the filtrates of cells exposed for 2 h in 200 muM copper and 24 h in 200 muM lead were 51 and 14 muM, respectively. The implication of the complexation shown by these soluble compounds in the bioavailability of heavy metals is discussed.