Isolation and characterization of nickel-accumulating yeasts

We selected three yeast strains that efficiently remove heavy metal ions from aqueous solution. We first screened yeasts that grew in the presence of 2 mM NiCl2 among our stock of wild yeasts, and then selected those that removed Ni most efficiently from aqueous solution. These strains also removed Cu and Zn from aqueous solution and were identified as Candida species. Ni uptake was efficient at pH between 4.0 and 7.0, but less efficient at pH below 3.0. The amount of Ni taken up by the yeast cells was proportional to the initial concentration of NiCl2 below about 4 mM Ni. The cells retained the abilities to remove Ni after treatment with 10 mM EDTA or 1 M HCl for repeated usage, or after heat treatment.