Chromium(III) and (VI) tolerance and bioaccumulation in yeast: a survey of cellular chromium content in selected strains of representative genera

Fifty-one wild type, naturally occurring yeast strains belonging to various systematic groups were screened for chromium(III) and (VI) uptake at growth-inhibitory concentrations of the metal. Yeast cells were supplemented with Cr at the moment of inoculation with 0.03 mg d.w. biomass/ml and then cultivated for 3 days in optimal growth media. The tolerance to Cr varied depending on the strain tested and the yeast cultures proved to be generally more sensitive to Cr(VI) (concentration range: 0.1–0.5 mM) than to Cr(III) (0.25–5 mM). The levels of cellular Cr content ranged from 0.29 to 11.10 mg/g d.w. and 0.21–3.3 mg/g d.w. for Cr(III) and Cr(VI), respectively. Distribution diagrams of the cell-accumulated Cr were constructed for the tested strain population, and the general uptake tendency of middle-range amounts of Cr(III), and low-range levels of Cr(VI) was revealed. The cell-accumulated Cr levels were similar at identical, non-toxic concentrations of either Cr form supplemented to the medium. Electron microscopic images proved that cytoplasm and cellular organelles were the ultimate targets for accumulation of both valences of the metal. The extreme cases of the strains revealing either the lowest or the highest Cr tolerance and uptake capabilities are discussed in terms of possible bioremediation mechanisms. The applicability of the strains in both environmental and nutritional practice was also considered.