Kang Chunxi, Wu Pingxiao, Li Liping, Yu Langfeng, Ruan Bo, Gong Beini, Zhu Nengwu
School of Environment and Energy, South China University of Technology, Guangzhou Higher Education Mega Centre, Guangzhou, 510006, People's Republic of China.
The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, South China University of Technology, Guangzhou Higher Education Mega Centre, Guangzhou, 510006, People's Republic of China.
Environ Sci Pollut Res Int. 2017 Feb;24(6):5949-5963. doi: 10.1007/s11356-016-8356-8. Epub 2017 Jan 9.
The aim of this study was to investigate the mechanism of Cr(VI) reduction and Cr(III) immobilization by resting cells of Pseudomonas aeruginosa using batch experiments and analysis techniques. Data showed that resting cells of this strain (3.2 g/L dry weight) reduced 10 mg/L of Cr(VI) by 86% in Tris-HCl buffer solution under optimized conditions of 5 g/L of sodium acetate as an electron donor, pH of 7.0 and temperature of 37 °C within 24 h. Cr(VI) was largely converted to nontoxic Cr(III), and both soluble crude cell-free extracts and membrane-associated fractions were responsible for Cr(VI) reduction. While remnant Cr(VI) existed only in the supernatant, the content of resultant Cr(III) in supernatant, on cell surface and inside cells was 2.62, 1.06, and 5.07 mg/L, respectively, which was an indicative of extracellular and intracellular reduction of chromate. Scanning electron microscopy analysis combined with energy dispersive X-ray spectroscopy revealed the adsorption of chromium on the bacterial surface. Interaction between Cr(III) and cell surface functional groups immobilized Cr(III) as indicated by Fourier transform infrared analyses and X-ray photoelectron spectroscopy. Transmission electron microscopy revealed Cr(III) precipitates in bacterial interior suggesting that Cr(II) could also be intracellularly accumulated. Thus, it can be concluded that interior and exterior surfaces of resting P. aeruginosa cells were sites for reduction and immobilization of Cr(VI) and Cr(III), respectively. This is further insight into the underlying mechanisms of microbial chromate reduction.
本研究的目的是通过批次实验和分析技术，探究铜绿假单胞菌静息细胞还原六价铬及固定三价铬的机制。数据表明，在以5 g/L乙酸钠作为电子供体、pH值为7.0、温度为37℃的优化条件下，该菌株的静息细胞（干重3.2 g/L）在24小时内可将Tris-HCl缓冲溶液中10 mg/L的六价铬还原86%。六价铬大部分转化为无毒的三价铬，可溶性粗无细胞提取物和膜相关组分均参与六价铬的还原。虽然残余的六价铬仅存在于上清液中，但上清液、细胞表面和细胞内三价铬的含量分别为2.62、1.06和5.07 mg/L，这表明铬酸盐在细胞外和细胞内均发生了还原。扫描电子显微镜分析结合能量色散X射线光谱揭示了铬在细菌表面的吸附。傅里叶变换红外分析和X射线光电子能谱表明，三价铬与细胞表面官能团之间的相互作用固定了三价铬。透射电子显微镜显示细菌内部有三价铬沉淀，表明二价铬也可在细胞内积累。因此，可以得出结论，铜绿假单胞菌静息细胞的内表面和外表面分别是六价铬还原和三价铬固定的位点。这进一步深入了解了微生物还原铬酸盐的潜在机制。
