Uranium(VI) interactions with Pseudomonas sp. PS-0-L, V4-5-SB and T5-6-I

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 in-fluence radionuclide biogeochemistry in boreal environment. Here, uranium (U(VI)) bioassociation by Pseudo-monas 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 mi-croscopy 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).

Automated summary

This study investigated the uranium bioassociation by Pseudomonas sp. isolated from a boreal bog. The strains were able to remove uranium from the solution, and the efficiency of uranium bioassociation was influenced by nutrient source, incubation temperature, time, and pH. Infrared spectroscopy and transmission electron microscopy with energy dispersive X-ray spectroscopy revealed that carboxyl groups on the cell surface and phosphate groups inside the cells were responsible for uranium binding. The removal efficiency of uranium depended on the U(VI) speciation under different pH conditions.