Immobilization of long-lived radionuclides Eu-152,Eu-154 by selective bioaccumulation in Saccharomyces cerevisiae from a synthetic mixture of Eu-152,Eu-154, Cs-137 and Co-60
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Yeast cells of Saccharomyces cerevisiae were found to accumulate Eu-152.154 radioisotopes selectively from a synthetic mixture of Eu-152.154, Cs-137, and Co-60 radiotracers at neutral pH in both trace and macro level. The extent of Eu uptake increased with time. The uptake of Co was observed only when concentration of cobalt was more than 10 mg kg(-1) at pH 6.5. None of the strains selected in our study showed any accumulation for Cs, even at trace level. Transmission electron microscopic (TEM) images of thin sections of the Eu accumulated yeast strains showed that it was accumulated inside the cell. The growth of four different strains of Saccharomyces cerevisiae was monitored at different concentrations of these metal salts. The yeast cells can grow upto 4.6 mM (700 mg kg(-1)) Eu concentration and 7.3 mM (1 g kg(-1)) Cs concentration irrespective of their histidine auxotrophy. In agreement with earlier reports it was observed that at 1.2 mM Co concentration, His' could grow at a pH range 5-6.5, whereas His(-) strains could not grow at any pH. Thus, the mechanism of uptake of the rare earth element, Eu, was found to follow a different pathway than the transition element Co, which causes toxicity to yeast cells in the absence of histidine in the biosynthetic pathway. The result may encourage for pilot experiments in preconcentration of rare earths using bioreagents in commercial scale.
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