title: Microbial extracellular polymeric substances reduce Ag+ to silver nanoparticles and antagonize bactericidal activity.
abstract: 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(+).
authors: State Key Laboratory of Pollution Control and Resource Reuse/School of the Environment, Nanjing University , Nanjing, Jiangsu 210046, People's Republic of China.
authors: Fuxing
authors: F
authors: Kang
authors: Pedro J
authors: PJ
authors: Alvarez
authors: Dongqiang
authors: D
authors: Zhu
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry*; D001704:Biopolymers / Q000737:chemistry* / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D053768:Metal Nanoparticles / Q000737:chemistry*; D046529:Microscopy, Electron, Transmission; D056951:Photoelectron Spectroscopy; D012834:Silver / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D000900:Anti-Bacterial Agents; D001704:Biopolymers; D012834:Silver