Horiike Takumi, Dotsuta Yuma, Nakano Yuriko, Ochiai Asumi, Utsunomiya Satoshi, Ohnuki Toshihiko, Yamashita Mitsuo
Rare Metal Bioresearch Center, Research Organization for Advanced Engineering, Shibaura Institute of Technology, Saitama, Japan.
Department of Chemistry, Kyushu University, Fukuoka, Japan.
Appl Environ Microbiol. 2017 Sep 29;83(20). doi: 10.1128/AEM.00855-17. Print 2017 Oct 15.
Radioactive strontium (Sr) leaked into saline environments, including the ocean, from the Fukushima Daiichi Nuclear Power Plant after a nuclear accident. Since the removal of Sr using general adsorbents (e.g., zeolite) is not efficient at high salinity, a suitable alternative immobilization method is necessary. Therefore, we incorporated soluble Sr into biogenic carbonate minerals generated by urease-producing microorganisms from a saline solution. An isolate, sp. strain TK2d, from marine sediment removed >99% of Sr after contact for 4 days in a saline solution (1.0 × 10 mol liter of Sr, 10% marine broth, and 3% [wt/vol] NaCl). Transmission electron microscopy and energy-dispersive X-ray spectroscopy showed that Sr and Ca accumulated as phosphate minerals inside the cells and adsorbed at the cell surface at 2 days of cultivation, and then carbonate minerals containing Sr and Ca developed outside the cells after 2 days. Energy-dispersive spectroscopy revealed that Sr, but not Mg, was present in the carbonate minerals even after 8 days. X-ray absorption fine-structure analyses showed that a portion of the soluble Sr changed its chemical state to strontianite (SrCO) in biogenic carbonate minerals. These results indicated that soluble Sr was selectively solidified into biogenic carbonate minerals by the TK2d strain in highly saline environments. Radioactive nuclides (Cs, Cs, and Sr) leaked into saline environments, including the ocean, from the Fukushima Daiichi Nuclear Power Plant accident. Since the removal of Sr using general adsorbents, such as zeolite, is not efficient at high salinity, a suitable alternative immobilization method is necessary. Utilizing the known concept that radioactive Sr is incorporated into bones by biomineralization, we got the idea of removing Sr via incorporation into biominerals. In this study, we revealed the ability of the isolated ureolytic bacterium to remove Sr under high-salinity conditions and the mechanism of Sr incorporation into biogenic calcium carbonate over a longer duration. These findings indicated the mechanism of the biomineralization by the urease-producing bacterium and the possibility of the biomineralization application for a new purification method for Sr in highly saline environments.
放射性锶（Sr）在核事故后从福岛第一核电站泄漏到包括海洋在内的盐环境中。由于使用普通吸附剂（如沸石）去除高盐度环境中的锶效率不高，因此需要一种合适的替代固定化方法。因此，我们将可溶性锶掺入由产脲酶微生物从盐溶液中生成的生物源碳酸盐矿物中。从海洋沉积物中分离出的一株菌株TK2d，在盐溶液（1.0×10摩尔/升的锶、10%的海水肉汤和3%[重量/体积]的氯化钠）中接触4天后，去除了>99%的锶。透射电子显微镜和能量色散X射线光谱分析表明，在培养2天时，锶和钙以磷酸盐矿物的形式在细胞内积累并吸附在细胞表面，然后在2天后细胞外形成了含有锶和钙的碳酸盐矿物。能量色散光谱分析表明，即使在8天后，碳酸盐矿物中仍存在锶，而不存在镁。X射线吸收精细结构分析表明，一部分可溶性锶在生物源碳酸盐矿物中转变为菱锶矿（SrCO）的化学状态。这些结果表明，在高盐环境中，可溶性锶被TK2d菌株选择性地固化到生物源碳酸盐矿物中。放射性核素（Cs、Cs和Sr）在福岛第一核电站事故后泄漏到包括海洋在内的盐环境中。由于使用普通吸附剂（如沸石）去除高盐度环境中的锶效率不高，因此需要一种合适的替代固定化方法。利用放射性锶通过生物矿化作用掺入骨骼这一已知概念，我们想到了通过掺入生物矿物来去除锶的想法。在本研究中，我们揭示了分离出的解脲细菌在高盐度条件下去除锶的能力以及在更长时间内锶掺入生物源碳酸钙的机制。这些发现表明了产脲酶细菌生物矿化的机制以及生物矿化应用于高盐环境中锶新净化方法的可能性。
