title: Bioprecipitation of uranium from alkaline waste solutions using recombinant Deinococcus radiodurans.
abstract: Bioremediation of uranium (U) from alkaline waste solutions remains inadequately explored. We engineered the phoK gene (encoding a novel alkaline phosphatase, PhoK) from Sphingomonas sp. for overexpression in the radioresistant bacterium Deinococcus radiodurans. The recombinant strain thus obtained (Deino-PhoK) exhibited remarkably high alkaline phosphatase activity as evidenced by zymographic and enzyme activity assays. Deino-PhoK cells could efficiently precipitate uranium over a wide range of input U concentrations. At low uranyl concentrations (1 mM), the strain precipitated >90% of uranium within 2h while a high loading capacity of around 10.7 g U/g of dry weight of cells was achieved at 10 mM U concentration. Uranium bioprecipitation by Deino-PhoK cells was not affected in the presence of Cs and Sr, commonly present in intermediate and low level liquid radioactive waste, or after exposure to very high doses of ionizing radiation. Transmission electron micrographs revealed the extracellular nature of bioprecipitated U, while X-ray diffraction and fluorescence analysis identified the precipitated uranyl phosphate species as chernikovite. When immobilized into calcium alginate beads, Deino-PhoK cells efficiently removed uranium, which remained trapped in beads, thus accomplishing physical separation of precipitated uranyl phosphate from solutions. The data demonstrate superior ability of Deino-PhoK, over earlier reported strains, in removal of uranium from alkaline solutions and its potential use in bioremediation of nuclear and other waste.
authors.affiliation: Molecular Biology Division, Bhabha Atomic Research Centre, Mumbai 400085, India.
authors.forename: Sayali
authors.initials: S
authors.lastname: Kulkarni
authors.forename: Anand
authors.initials: A
authors.lastname: Ballal
authors.forename: Shree Kumar
authors.initials: SK
authors.lastname: Apte
mesh_terms: D000464:Alginates / Q000737:chemistry; D000469:Alkaline Phosphatase / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism; D001673:Biodegradation, Environmental; D034301:Deinococcus / Q000378:metabolism*; D004307:Dose-Response Relationship, Radiation; D020723:Glucuronic Acid / Q000737:chemistry; D006603:Hexuronic Acids / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008670:Metals / Q000737:chemistry; D046529:Microscopy, Electron, Transmission; D008856:Microscopy, Fluorescence; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011850:Radioactive Waste; D011994:Recombinant Proteins / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D020578:Sphingomonas / Q000378:metabolism; D013997:Time Factors; D014501:Uranium / Q000032:analysis* / Q000737:chemistry; D062065:Wastewater; D014875:Water Pollutants, Radioactive / Q000032:analysis*; D018508:Water Purification / Q000379:methods*; D014961:X-Ray Diffraction
chemical_list: D000464:Alginates; D000469:Alkaline Phosphatase; D001426:Bacterial Proteins; D020723:Glucuronic Acid; D006603:Hexuronic Acids; D008670:Metals; D010744:Phosphoric Monoester Hydrolases; D011850:Radioactive Waste; D011994:Recombinant Proteins; D014501:Uranium; D062065:Wastewater; D014875:Water Pollutants, Radioactive
keywords: Alkaline solutions; Bioprecipitation; Deinococcus radiodurans; Uranium