Accumulation of yttrium by Variovorax paradoxus

We screened oligotrophic microorganisms for those which were capable of red ucing the concentration of yttrium (Y), a representative of the rare-earth elements, in culture medium. From 465 strains of oligotrophic microorganism s (grown on 1/100 diluted nutrient agar) isolated from soil and river water samples, 7 strains capable of reducing the concentration of Y in the dilut ed nutrient broth containing 5 ppm Y were selected. Three strains capable o f reducing the concentration of Y to a great extent were identified as Vari ovorax paradoxus (strain Y-1) and Comamonas acidovorans (strains Y-2 and Y- 3). Energy dispersive X-ray analyses revealed that V. paradoxus Y-1 incorpo rated Y into both the cell and excreted materials. The three strains tended to reduce the concentrations of mostly light rare-earth elements such as L a, Ce, Pr and Nd, and intermediate elements such as Tb, Dy, Ho and Er to so me extent, but did not reduce the concentrations of heavy elements such as Tm, Yb and Lu. Although V. paradoxus Y-1 could not reduce the concentration of trivalent metal ions such as Fe3+ and Cr3+ (5 ppm) which were added ind ividually to the 1/100 diluted nutrient broth, when both Y and Fe3+ or Cr3 were added to the broth, the concentration of Fe3+- for Cr3+ was reduced c oncomitantly with that of Y. In the case of divalent metal ions such as Mn2 +, Cu2+ and Fe2+, such a phenomenon was not observed. Y induced the product ion of the extracellular materials by V. paradoxus Y-1, suggesting that Y m ight affect the physiological activity of this strain.