Aerobic uranium (VI) bioprecipitation by metal‐resistant bacteria isolated from radionuclide‐ and metal‐contaminated subsurface soils

Abstract

Summary In this study, the immobilization of toxic uranium (U(VI)) mediated by the intrinsic phosphatase acti- vities of naturally occurring bacteria isolated from contaminated subsurface soils was examined. The phosphatase phenotypes of strains belonging to the genera, Arthrobacter, Bacillus and Rahnella, previ- ously isolated from subsurface soils at the US Depart- ment of Energy's (DOE) Oak Ridge Field Research Center (ORFRC), were determined. The ORFRC repre- sents a unique, extreme environment consisting of highly acidic soils with co-occurring heavy metals, radionuclides and high nitrate concentrations. Iso- lates exhibiting phosphatase-positive phenotypes indicative of constitutive phosphatase activity were subsequently tested in U(VI) bioprecipitation assays. When aerobically grown in synthetic groundwater (pH 5.5) amended with 10 mM glycerol-3-phosphate (G3P), phosphatase-positive Bacillus and Rahnella spp. strains Y9-2 and Y9602 liberated sufficient phos- phate to precipitate 73% and 95% of total soluble U added as 200 mM uranyl acetate respectively. In contrast, an Arthrobacter sp. X34 exhibiting a phosphatase-negative phenotype did not liberate phosphate from G3P or promote U(VI) precipitation. This study provides the first evidence of U(VI) precipi- tation via the phosphatase activity of naturally occur- ring Bacillus and Rahnella spp. isolated from the acidic subsurface at the DOE ORFRC.