Morcillo Fernando, González-Muñoz María T, Reitz Thomas, Romero-González María E, Arias José M, Merroun Mohamed L
Departamento de Microbiología, Universidad de Granada, Granada, Spain.
Institute of Resource Ecology, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany.
PLoS One. 2014 Mar 11;9(3):e91305. doi: 10.1371/journal.pone.0091305. eCollection 2014.
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 5·10(-4) to 10(-5) M (environmentally relevant concentrations), XAS analysis revealed that uranyl phosphate mineral phases, structurally resembling meta-autunite [Ca(UO2)2(PO4)2 2-6H2O] 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] = 5·10(-4) 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.
本研究的主要目标是比较pH值、铀浓度和背景电解质（海水和高氯酸钠溶液）对与海洋细菌深海嗜压菌MAH1相关的铀(VI)形态的影响。这是在分子水平上通过结合X射线吸收光谱法（XAS）、时间分辨激光诱导荧光光谱法（TRLFS）和高分辨率透射电子显微镜（HRTEM）的多学科方法完成的。我们表明，U(VI)/细菌的相互作用机制高度依赖于pH值，而且所用背景电解质的性质也起到了作用。在中性条件下且铀浓度范围为5·10⁻⁴至10⁻⁵ M（环境相关浓度）时，XAS分析表明，在菌株MAH1的细胞表面沉淀出结构类似于变钙铀云母[Ca(UO₂)₂(PO₄)₂·2 - 6H₂O]的磷酸铀酰矿物相。这种矿物相的形成与背景溶液无关，但U(VI)发光寿命分析表明，海水样品中的U(VI)形态更为复杂，即在自然条件下形成了不同的络合物。在酸性条件下，pH值为2、3和4.3（[U] = 5·10⁻⁴ M，背景电解质 = 0.1 M高氯酸钠）时，溶液中铀的去除是由于对细胞外多糖（EPS）和细胞壁成分的生物吸附，这从TEM分析中可以明显看出。LIII边XAS和TRLFS研究表明，观察到的生物吸附过程依赖于pH值。细菌细胞在pH值为2时通过有机磷酸基团与铀形成络合物，在pH值为3和4.3时分别通过磷酸基团和羧基与铀形成络合物。与高氯酸钠溶液相比，海水中铀与细菌形成的络合物的差异表明，锕系元素/微生物相互作用受三个研究因素的影响，即pH值、铀浓度和溶液的化学成分。
