Resistance to Cadmium Ions and Formation of a Cadmium-Binding Complex in Various Wild-Type Yeasts

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The resistance to cadmium ions (Cd-resistance) and possible formation of cadmium-binding complexes were examined in eight different wild-type yeasts. Saccharomyces exiguus. Pichia farinosa, Torulaspora delbrueckii and Schizosaccharomyces octosporus exhibited partial Cd-resistance, as compared to the Cd-resistant strain 301N and the Cu-resistant but Cd-sensitive strain X2180-1B of Saccharomyces cerevisiae. Saccharomyces carlsbergensis, Pichia mogii, Zygosaccharomyces rouxii and Kluyveromyces lactis were all Cd-sensitive. The partially Cd-sensi-tive species, with the exception of S. exiguus, accumulated Cd^<2+> ions in the cytoplasmic fraction to varying extents. This fraction from S. octosporus included a Cd-binding complex that contained (γEC)_nG peptides known as cadystins or phytochelatins, while P.farinosa and T. delbru-eckii synthesized Cd-binding proteins that were similar to the Cd-metallothionein produced by S. cerevisiae 301N in terms of molecular weight and amino acid composition. These results suggest that such cytoplasmic molecules play a role in the Cd-tolerance of the above three species of yeast. S. exiguus retained most cadmium in the cell wall fraction and no Cd-binding complex was found in the cytoplasm, an indication of the important role of the cell wall in its Cd-tolerance. Different modes of binding of Cd^<2+> ions appear to be involved in the Cd-resistance of wild-type yeasts and fungi.
日本植物生理学会の論文