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Pseudomonas sp. are indigenous inhabitants of ombrotrophic bogs which can survive in acidic, nutrient-poor environments with wide temperature fluctuations. Their interactions with contaminant radionuclides can influence radionuclide biogeochemistry in boreal environment. Here, uranium (U(VI)) bioassociation by Pseudomonas sp. PS-0-L, V4-5-SB and T5-6-I isolated from a boreal bog was studied by a combination of batch contact experiments, spectroscopy and microscopy. All strains removed U from the solution and the U bioassociation efficiency was affected by the nutrient source, incubation temperature, time and pH. Highest U bioassociation occurred in the strains PS-0-L (0.199 mg U/gBDW) and V4-5-SB (0.223 mg U/gBDW). Based on in-situ attenuated total reflection Fourier transformation infrared spectroscopy (ATR FT-IR) analyses, the most likely functional groups responsible for U binding were the cell surface carboxyl groups. In addition, transmission electron microscopy with energy dispersive X-ray spectroscopy (TEM/EDX) showed dense intra-cellular round- and needle-like U accumulations in the cytoplasm and near to the inner cell membrane. The presence of U with phosphorus was indicated in elemental mapping. Modelled data showed ≡SOOHx-1 and ≡SOCO2Hx-1 as the dominant surface sites, contributing to the negative cell surface charge. The U removal efficiency depended on the U(VI) speciation under different pH conditions. At pH 5, the main species reacting with bacterial cell surfaces was UO22+, while at pH 9 UO2(OH)2 and UO2(OH)3- dominated the reactions. Further, U bioassociation increased with increasing aqueous U(VI) concentrations. Our data suggests U bioassociation on 1) outer cell membrane/cell wall associated carboxyl groups (e.g., proteins), and 2) intracellular phosphate groups (e.g., phospholipids).

An assessment of old and current mine tailings in Finland has shown that they have economic potential, with the metallic value being hundreds of millions of euros. Samples of acidic waters from the Pyhasalmi mine were analysed for bioleaching microorganisms and then used in bioleaching experiments using pyrite and pyrrhotite tailings from four Finnish mines. A high bacterial and fungal diversity was found in the mine water: Acidithiobacillus and Leptospirillum dominated the mine water 240 m below the surface, Leptospirillum dominated at 500 m below the surface, and Ferrovum and Metallibacter were dominant at 600 m below the surface. The bioleaching experiments showed that three of the tailings samples had rapid decrease of pH and increase of redox-potential, suggesting sulphide mineral dissolution, and resulting in iron oxidation and sulphuric acid production. For Tailing 4, no major pH decrease or redox-potential increase was observed, even though the material contained several wt% of pyrrhotite. Zn yields for Tailings 1 were 85% in 5 days, with low Ni and Co. Tailings 2 had a Zn yield of 100% in 18 days, and Tailing 3 had a Zn yield of 78% in 32 days., An assessment of old and current mine tailings in Finland has shown that they have economic potential, with the metallic value being hundreds of millions of euros. Samples of acidic waters from the Pyhasalmi mine were analysed for bioleaching microorganisms and then used in bioleaching experiments using pyrite and pyrrhotite tailings from four Finnish mines. A high bacterial and fungal diversity was found in the mine water: Acidithiobacillus and Leptospirillum dominated the mine water 240 m below the surface, Leptospirillum dominated at 500 m below the surface, and Ferrovum and Metallibacter were dominant at 600 m below the surface. The bioleaching experiments showed that three of the tailings samples had rapid decrease of pH and increase of redox-potential, suggesting sulphide mineral dissolution, and resulting in iron oxidation and sulphuric acid production. For Tailing 4, no major pH decrease or redox-potential increase was observed, even though the material contained several wt% of pyrrhotite. Zn yields for Tailings 1 were 85% in 5 days, with low Ni and Co. Tailings 2 had a Zn yield of 100% in 18 days, and Tailing 3 had a Zn yield of 78% in 32 days.

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