Geomicrobiology Laboratory, State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences , Beijing 100083, China.
Department of Geology and Environmental Earth Science, Miami University , Oxford, Ohio 45056, United States.
Environ Sci Technol. 2017 Jul 5;51(13):7639-7647. doi: 10.1021/acs.est.7b00726. Epub 2017 Jun 13.
Previous work documented the general antibacterial mechanism of iron containing clays that involved hydroxyl radical (•OH) production from soluble Fe, and attack of cell membrane and intracellular proteins. Here we explore the role of clay structural Fe(II) in •OH production at near neutral pH and identify a lipid involved in the antibacterial process. Structural Fe(III) in nontronite NAu-2 was reduced (rNAu-2) and E. coli, a model bacterium, was exposed to rNAu-2 in oxic suspension. The antibacterial activity of rNAu-2 was dependent on pH and Fe(II) concentration, where E. coli were completely killed at pH 6, but survived at pH 7 and 8. In the presence of a •OH scavenger or in anaerobic atmosphere, E. coli survived better, suggesting that cell death may be caused by •OH generated from oxidation of structural Fe(II) in rNAu-2. In-situ imaging revealed damage of a membrane lipid, cardiolipin, in the polar region of E. coli cells, where reactive oxygen species and redox-active labile Fe were enriched. Our results advance the previous antibacterial model by demonstrating that the structural Fe(II) is the primary source of •OH, which damages cardiolipin, triggers the influx of soluble Fe into the cell, and ultimately leads to cell death.
先前的工作记录了含铁矿黏土的一般抗菌机制，该机制涉及可溶性 Fe 产生羟基自由基 (•OH)，以及攻击细胞膜和细胞内蛋白质。在这里，我们探讨了近中性 pH 下黏土结构 Fe(II)在 •OH 产生中的作用，并确定了一个参与抗菌过程的脂质。非钠蒙脱石 NAu-2 中的结构 Fe(III)被还原（rNAu-2），并将其暴露于有氧悬浮液中的大肠杆菌，一种模型细菌。rNAu-2 的抗菌活性取决于 pH 值和 Fe(II)浓度，在 pH 6 时大肠杆菌完全被杀死，但在 pH 7 和 8 时存活。在 •OH 清除剂或厌氧气氛存在的情况下，大肠杆菌的存活能力更好，这表明细胞死亡可能是由 rNAu-2 中结构 Fe(II)氧化产生的 •OH 引起的。原位成像揭示了细胞膜脂质心磷脂在大肠杆菌细胞极性区域的损伤，其中富含活性氧和氧化还原活性不稳定的 Fe。我们的结果通过证明结构 Fe(II)是 •OH 的主要来源，进一步推进了先前的抗菌模型，•OH 会损伤心磷脂，引发可溶性 Fe 涌入细胞，并最终导致细胞死亡。
