21 research outputs found
Biosorption and Biomineralization of U(VI) by the Marine Bacterium Idiomarina loihiensis MAH1: Effect of Background Electrolyte and pH
The main goal of this study is to compare the effects of pH, uranium concentration, and background electrolyte (seawater and NaClO4 solution) on the speciation of uranium(VI) associated with the marine bacterium Idiomarina loihiensis MAH1. This was done at the molecular level using a multidisciplinary approach combining X-ray Absorption Spectroscopy (XAS), Time-Resolved Laser-Induced Fluorescence Spectroscopy (TRLFS), and High Resolution Transmission Electron Microscopy (HRTEM). We showed that the U(VI)/bacterium interaction mechanism is highly dependent upon pH but also the nature of the used background electrolyte played a role. At neutral conditions and a U concentration ranging from 5·10â4 to 10â5 M (environmentally relevant concentrations), XAS analysis revealed that uranyl phosphate mineral phases, structurally resembling meta-autunite [Ca(UO2)2(PO4)2 2â6H2O] are precipitated at the cell surfaces of the strain MAH1. The formation of this mineral phase is independent of the background solution but U(VI) luminescence lifetime analyses demonstrated that the U(VI) speciation in seawater samples is more intricate, i.e., different complexes were formed under natural conditions. At acidic conditions, pH 2, 3 and 4.3 ([U] = 5·10â4 M, background electrolyte = 0.1 M NaClO4), the removal of U from solution was due to biosorption to Extracellular Polysaccharides (EPS) and cell wall components as evident from TEM analysis. The LIII-edge XAS and TRLFS studies showed that the biosorption process observed is dependent of pH. The bacterial cell forms a complex with U through organic phosphate groups at pH 2 and via phosphate and carboxyl groups at pH 3 and 4.3, respectively. The differences in the complexes formed between uranium and bacteria on seawater compared to NaClO4 solution demonstrates that the actinide/microbe interactions are influenced by the three studied factors, i.e., the pH, the uranium concentration and the chemical composition of the solution.This work was funded by the grants CGL2009-09760 and CGL2012-36505 (Ministerio de Ciencia e InnovaciĂłn), and RNM 3943 (Junta de AndalucĂa), Spain
Metabolism-dependent bioaccumulation of uranium by Rhodosporidium toruloides isolated from the flooding water of a former uranium mine
Remediation of former uranium mining sites represents one of the biggest challenges worldwide
that have to be solved in this century. During the last years, the search of alternative
strategies involving environmentally sustainable treatments has started. Bioremediation,
the use of microorganisms to clean up polluted sites in the environment, is considered one
the best alternative. By means of culture-dependent methods, we isolated an indigenous
yeast strain, KS5 (Rhodosporidium toruloides), directly from the flooding water of a former
uranium mining site and investigated its interactions with uranium. Our results highlight
distinct adaptive mechanisms towards high uranium concentrations on the one hand, and
complex interaction mechanisms on the other. The cells of the strain KS5 exhibit high a
uranium tolerance, being able to grow at 6 mM, and also a high ability to accumulate this
radionuclide (350 mg uranium/g dry biomass, 48 h). The removal of uranium by KS5 displays
a temperature- and cell viability-dependent process, indicating that metabolic activity
could be involved. By STEM (scanning transmission electron microscopy) investigations,
we observed that uranium was removed by two mechanisms, active bioaccumulation and
inactive biosorption. This study highlights the potential of KS5 as a representative of indigenous
species within the flooding water of a former uranium mine, which may play a key role
in bioremediation of uranium contaminated sites.This work was supported by the
Bundesministerium fĂŒr Bildung und Forschung
grand nÂș 02NUK030F (TransAqua). Further support
took place by the ERDF-co-financed Grants
CGL2012-36505 and 315 CGL2014-59616R,
Ministerio de Ciencia e InnovaciĂłn, Spain