The deep geological repository (DGR) system is widely accepted as the solution for the disposal of radioactive wastes in the future. This concept is based on several natural and engineered barriers such as bentonite clays, which will encase the metal containers holding the radioactive waste. Microorganisms living therein can influence the mobility of the radionuclides (e.g. selenium, uranium, etc.) present in such residues. In this work the bentonite isolate Stenotrophomonas bentonitica is shown to reduce selenite (Se^IV) to elemental Se (Se⁰) nanostructures (amorphous and trigonal) and to volatile methylated Se^−II species. Electron microscopy (HAADF-STEM) analysis of purified Se nanostructures supported the transformation process from amorphous to trigonal Se, proposed in previous studies. Infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) revealed the presence of amine rich organic matter, covering the nanostructures, suggesting the role of proteins in their synthesis and transformation. In addition, X-ray absorption spectroscopy (XAS) of SeNPs associated to the cells confirmed the formation of different Se⁰ structures (amorphous and crystalline). Finally, the reduction of Se^IV to volatile methylated species (DMDSe and DMSeS) was detected using a gas chromatography-mass spectrometry (GC-MS) system. The oxidation state and molecular coordination of Se in the purified Se nanostructures as well as the volatile Se species, by means of microscopic, spectroscopic, and gas chromatographic techniques, indicated their lower mobility and chemo-toxicity. This study thus highlights the potential environmental significance of microbial processes for the mobility and toxicity of selenium in future repositories, which in turn contribute to their safe implementation.

中文翻译：

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斑节单胞菌转化为Se0纳米结构和挥发性Se物种的SeIV生物转化的化学和结构表征

深层地质处置库（DGR）系统已被广泛接受为未来放射性废物处置的解决方案。该概念基于几种天然和工程隔离层，例如膨润土，它将包裹装有放射性废物的金属容器。生活在其中的微生物会影响此类残留物中存在的放射性核素（例如，硒，铀等）的迁移率。在这项工作中，膨润土分离物Stenotrophomonas bentonitica被证明可以将亚硒酸盐（Se ^IV）还原为元素Se（Se ⁰）纳米结构（无定形和三角形）以及挥发性甲基化的Se ^-II种类。电子显微镜（HAADF-STEM）对纯化的硒纳米结构的分析支持了先前研究中提出的从无定形到三角硒的转化过程。红外光谱（ATR-FTIR）和X射线光电子能谱（XPS）揭示了富含胺的有机物的存在，覆盖了纳米结构，表明蛋白质在其合成和转化中的作用。此外，与细胞相关的SeNP的X射线吸收光谱（XAS）证实了不同的Se ⁰结构（非晶和晶体）的形成。最后，还原硒^四使用气相色谱-质谱（GC-MS）系统检测到挥发性甲基化物质（DMDSe和DMSeS）的残留量。借助显微，光谱和气相色谱技术，纯化的硒纳米结构以及挥发性硒物种中硒的氧化态和分子配位表明它们的迁移率和化学毒性较低。因此，这项研究强调了微生物过程对于未来储存库中硒的迁移和毒性的潜在环境意义，这反过来又有助于其安全实施。