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Do lead and iron share a similar pattern in their toxicity to the Saccharomyces cerevisiae yeast?

Iron (Fe) is an essential metal required in trace amounts for cellular functions, but it can be highly toxic to cells because of the generation of oxygen radicals or anions. Led (Pb) is non-essential metal, has no known biological roles and it is highly toxic even at low concentration. In this study we have used the baker's yeast, Saccharomyces cerevisiae. It is an ideal model organism since it possesses effective mechanisms to negate metal toxicity and survive a broad range of toxic stress scenarios. It responds to metal exposure by arresting cell cycle progression and by adapting the transcriptome, proteome, and metabolome. Testing doses of metal ions were determined by Survival test (for Fe3+ 4 mM, for Pb2+ 8 mM) and used in further analyses. They provoked comparable values of S. cerevisiae growth inhibition (96% for Fe3+ and 94% for Pb2+, respectively), but different values in vitality measuring determined through the metabolic activity using yeast-specific dye FUN-1. % of metabolically active cells with preserved metabolic capability was lower in Pb2+ than in Fe3+ treated cells. Besides, the intracellular oxidation level in Pb2+ treated cells had higher values, indicating less efficient endogenous antioxidant defense systems in Pb2+ treatment. The effects of metal ions at the mitochondrial level were determined by using a proteomic approach. In the case of Pb2+ treated cells, 20 h after metal ions addition, downregulation of 15 and upregulation of 4 proteins compared to the control was observed. 3 downregulated proteins (Pda1_α, Ald4, Sco2) and 2 upregulated proteins (Eft1α, Lys12) were common with Fe3+ treated cells. Other downregulated proteins in Pb2+ treated cells are more important in combating the metal–ions provoked stress. These proteins belong to different cellular processes such as energy and carbohydrate metabolism (Atp2, Cit1, Cor1, Cox 6, Dld1, Qcr2, Qcr7, Tpi1), transport (Tom40), genetic information processing (Rim1) and oxidative stress response (Tsa2). The results of metabolic and proteomic tests point to the fact that Fe and Pb only partially share the similarity in their toxicity to the S. cerevisiae mainly because cells treated with Pb2+ showed less efficient defence systems.

lead, iron, toxicity, yeast, proteome

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