State Key Laboratory of Pollution Control and Resource Reuse/School of the Environment, Nanjing University , Nanjing, Jiangsu 210046, People's Republic of China.
Environ Sci Technol. 2014;48(1):316-22. doi: 10.1021/es403796x. Epub 2013 Dec 20.
Whereas the antimicrobial mechanisms of silver have been extensively studied and exploited for numerous applications, little is known about the associated bacterial adaptation and defense mechanisms that could hinder disinfection efficacy or mitigate unintended impacts to microbial ecosystem services associated with silver release to the environment. Here, we demonstrate that extracellular polymeric substances (EPS) produced by bacteria constitute a permeability barrier with reducing constituents that mitigate the antibacterial activity of silver ions (Ag(+)). Specifically, manipulation of EPS in Escherichia coli suspensions (e.g., removal of EPS attached to cells by sonication/centrifugation or addition of EPS at 200 mg L(-1)) demonstrated its critical role in hindering intracellular silver penetration and enhancing cell growth in the presence of Ag(+) (up to 0.19 mg L(-1)). High-resolution transmission electron microscopy (HRTEM) combined with X-ray photoelectron spectroscopy (XPS) and energy-dispersive spectrometry (EDS) analyses showed that Ag(+) was reduced to silver nanoparticles (AgNPs; 10-30 nm in diameter) that were immobilized within the EPS matrix. Fourier transform infrared (FTIR) and (13)C nuclear magnetic resonance (NMR) spectra suggest that Ag(+) reduction to AgNPs by the hemiacetal groups of sugars in EPS contributed to immobilization. Accordingly, the amount and composition of EPS produced have important implications on the bactericidal efficacy and potential environmental impacts of Ag(+).
尽管银的抗菌机制已经得到了广泛的研究和应用，但对于与银释放到环境中相关的细菌适应和防御机制知之甚少，这些机制可能会阻碍消毒效果或减轻对与微生物生态系统服务相关的银的意外影响。在这里，我们证明了细菌产生的胞外聚合物（EPS）构成了具有还原成分的渗透屏障，可减轻银离子（Ag(+））的抗菌活性。具体而言，通过超声处理/离心或在 200 mg L(-1) 添加 EPS 来操纵大肠杆菌悬浮液中的 EPS（例如，去除附着在细胞上的 EPS），证明了其在阻止细胞内银渗透和增强 Ag(+)存在下的细胞生长方面具有关键作用（高达 0.19 mg L(-1)）。高分辨率透射电子显微镜（HRTEM）结合 X 射线光电子能谱（XPS）和能谱分析（EDS）表明，Ag(+)被还原为银纳米颗粒（AgNPs；直径为 10-30nm），并固定在 EPS 基质中。傅里叶变换红外（FTIR）和（13）C 核磁共振（NMR）谱表明，EPS 中糖的半缩醛基团将 Ag(+)还原为 AgNPs 有助于固定化。因此，EPS 的产生量和组成对 Ag(+)的杀菌效果和潜在的环境影响具有重要意义。
