Effect of minerals on accumulation of Cs by fungus Saccaromyces cerevisiae

• Effect of minerals on the accumulation of radioactive Cs by yeast was studied.
• Presence of minerals reduced accumulation of radioactive Cs by yeast.
• The order of reduction is mica>smectite, illite>>vermiculite, phlogopite, zeolite.
• This order is inversely correlated to the adsorption ratio of the mineral.
• Yeast accumulates radioactive Cs competitively with minerals.

The accumulation of Cs by unicellular fungus of Saccharomyces cerevisiae in the presence of minerals has been studied to elucidate the role of microorganisms in the migration of radioactive Cs in the environment. Two different types of experiments were employed: experiments using stable Cs to examine the effect of a carbon source on the accumulation of Cs, and accumulation experiments of radioactive Cs from agar medium containing 137Cs and zeolite, vermiculite, phlogopite, smectite, mica, or illite as mineral supplements. In the former type of experiments, the Cs-accumulated cells were analyzed by scanning electron microscopy equipped with energy dispersive X-ray analysis (SEM-EDS). In the latter type, the radioactivity in the yeast cells was measured by an autoradiography technique.When a carbon source was present, higher amounts of Cs accumulated in the cells than in the resting condition without a carbon source. Analyses with SEM-EDS showed that no mineral formed on the cell surface. These results indicate that the yeast cells accumulate Cs by adsorption on the cell surface and intracellular accumulation. In the presence of minerals in the agar medium, the radioactivity in the yeast cells was in the order of mica > smectite, illite >> vermiculite, phlogopite, zeolite. This order is inversely correlated to the ratio of the concentration of radioactive Cs between the minerals and the medium solution. These results strongly suggest that the yeast accumulates radioactive Cs competitively with minerals.

Autoradiography analysis showed that presence of larger amounts of mineral of vermiculite collected in South Africa induced less accumulation of radioactive Cs in yeast cells from the medium.Figure optionsDownload as PowerPoint slide