John Wiley & Sons, Ltd.

Elucidating the genetic basis for E. coli defense against silver toxicity using mutant arrays

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Bacterial adaptation and defense mechanisms against silver are poorly understood at the genetic level. Using a library of E. coli gene‐deletion mutants, we 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 to 90.1 ± 5.4% survival for wild type E. coli, after 6‐h exposure to 8 mg/L AgNO3), 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). TEM with STEM/EDS analysis showed accumulation of silver nanoparticles (AgNPs) within EPS, suggesting that EPS serves as a protective barrier that also immobilizes dissolved silver as AgNPs. Environ Toxicol Chem © 2014 SETAC

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