title: Elucidating the genetic basis for Escherichia coli defense against silver toxicity using mutant arrays.
abstract: Bacterial adaptation and defense mechanisms against silver are poorly understood at the genetic level. A library of Escherichia coli gene-deletion mutants was used to show that clones lacking sodB (coding for oxidative stress protection), lon (protein damage repair), or cusR (metal efflux pump) are quite sensitive to silver (with 7.3 ± 9.1%, 5.3 ± 1.8%, and 0.4 ± 0.1% of cells surviving, respectively, compared with 90.1 ± 5.4% survival for wild-type E. coli, after 6-h exposure to 8 mg/L AgNO(3)), suggesting the importance of the coded functions as defense mechanisms. Mutants lacking pgaB or wcaD, which code for production of extracellular polymeric substances (EPS), also showed significant (p < 0.05) sensitivity to silver exposure (23.4 ± 16.2% and 23.1 ± 32.6% survival, respectively). Transmission electron microscopy (TEM) with scanning TEM/energy-dispersive X-ray spectroscopy analysis showed accumulation of silver nanoparticles within EPS, suggesting that EPS serve as a protective barrier that also immobilizes dissolved silver as silver nanoparticles.
authors.affiliation: Department of Civil and Environmental Engineering, Rice University, Houston, Texas, USA.
authors.forename: Zongming
authors.initials: Z
authors.lastname: Xiu
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Liu
authors.forename: Jacques
authors.initials: J
authors.lastname: Mathieu
authors.forename: Jing
authors.initials: J
authors.lastname: Wang
authors.forename: Dongqiang
authors.initials: D
authors.lastname: Zhu
authors.forename: Pedro J J
authors.initials: PJ
authors.lastname: Alvarez
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics* / Q000648:ultrastructure; D029968:Escherichia coli Proteins / Q000235:genetics; D017353:Gene Deletion; D005798:Genes, Bacterial; D053768:Metal Nanoparticles / Q000648:ultrastructure; D018384:Oxidative Stress; D012834:Silver / Q000633:toxicity*; D013482:Superoxide Dismutase / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D012834:Silver; C087504:SodB protein, Bacteria; D013482:Superoxide Dismutase
keywords: Adaptation; Antimicrobial; Extracellular polymeric substances; Mutants; Silver