Sani Rajesh K, Peyton Brent M, Dohnalkova Alice
Department of Chemical Engineering, Center for Multiphase Environmental Research, Washington State University, Dana Hall Room 118, Pullman, Washington 99164-2710, USA.
Environ Toxicol Chem. 2006 May;25(5):1231-8. doi: 10.1897/05-401r.1.
The toxic effects of U(VI) were studied using Desulfovibrio desulfuricans G20 in a medium containing bicarbonate or 1,4-piperazinediethane sulfonic acid disodium salt monohydrate (PIPES) buffer (each at 30 mM and pH 7). Uranium(VI) toxicity was dependent on the medium buffer and was observed in terms of longer lag times and, in some cases, no measurable growth. The minimum inhibiting concentration was 140 microM U(VI) in PIPES-buffered medium. This is 36-fold lower than that reported previously for D. desulfuricans. For all cases in which D. desulfuricans G20 grew in the presence of U(VI), the final cell protein yield was equivalent to that of the U(VI)-free control. In 24 h, D. desulfuricans G20 (total cell protein, 40 mg/L) removed 50 FiM U(VI) from solution in PIPES buffer, as compared to 96 microM U(VI) in bicarbonate buffer under anaerobic, nongrowth conditions. Even though the solubility of U(VI) was significantly lower in PIPES buffer than in bicarbonate buffer, U(VI) was much more toxic in PIPES buffer than in bicarbonate buffer. Analysis of thin sections of D. desulfuricans G20 treated with 90 microM U(VI) in medium containing PIPES buffer revealed that only a very small fraction of cells had reduced U precipitates in the periplasmic spaces. In the presence of bicarbonate buffer, however, reduced U was observed not only in the periplasm but also in the cytoplasm. Selected-area electron diffraction patterns and crystallographic analysis of transmission-electron microscopic lattice fringe images confirmed the structure of precipitated U in the cell periplasm and cytoplasm as being that of uraninite. These results suggest that U(VI) toxicity and the detoxification mechanisms of D. desulfuricans G20 depend greatly on the chemical forms of U(VI) that are present.
使用脱硫脱硫弧菌G20在含有碳酸氢盐或1,4 - 哌嗪二乙磺酸二钠盐一水合物（PIPES）缓冲液（均为30 mM，pH 7）的培养基中研究了U(VI)的毒性作用。U(VI)的毒性取决于培养基缓冲液，表现为较长的延迟期，在某些情况下，无法测量到生长。在PIPES缓冲培养基中，最小抑制浓度为140 μM U(VI)。这比先前报道的脱硫脱硫弧菌的浓度低36倍。对于脱硫脱硫弧菌G20在U(VI)存在下生长的所有情况，最终细胞蛋白产量与无U(VI)对照相当。在24小时内，脱硫脱硫弧菌G20（总细胞蛋白，40 mg/L）在PIPES缓冲液中从溶液中去除了50 μM U(VI)，而在厌氧、非生长条件下，在碳酸氢盐缓冲液中为96 μM U(VI)。尽管U(VI)在PIPES缓冲液中的溶解度明显低于在碳酸氢盐缓冲液中的溶解度，但U(VI)在PIPES缓冲液中的毒性比在碳酸氢盐缓冲液中高得多。对在含有PIPES缓冲液的培养基中用90 μM U(VI)处理的脱硫脱硫弧菌G20的薄片分析表明，只有极少数细胞在周质空间中有还原态U沉淀。然而，在碳酸氢盐缓冲液存在下，不仅在周质中观察到还原态U，在细胞质中也观察到了。选区电子衍射图谱和透射电子显微镜晶格条纹图像的晶体学分析证实，细胞周质和细胞质中沉淀的U的结构为晶质铀矿。这些结果表明，脱硫脱硫弧菌G20的U(VI)毒性和解毒机制在很大程度上取决于存在的U(VI)的化学形式。
