Summary
Growth of Escherichia coli in chloridefree medium in batch culture is inhibited completely at concentrations of AgNO3 greater than 2.5x10-6 M. Incubation of non-growing cells in HEPES buffer (pH 7.4) at increasing levels of Ag+ results in the progressive saturation of two types of binding site. At one site, the Ag+ is not released by washing with 0.1 M nitric acid, and is probably intracellular. Silver bound to the second site is released by acid-washing, but not by buffer washing, and is assumed to be surface-bound. The amounts of Ag+ taken up from solution at the two sites is 1.6x10-7 and 4.6x10-7 mol (mg dry weight)-1, respectively. Total accumulation of silver is 67 mg (g dry weight)-1, similar to literature values found for silver-resistant bacteria. Binding of Ag+ at intracellular sites (observed at low [Ag+]) appears to be independent of pH. Addition of AgNO3 to growing cells in mid-exponential phase of growth in concentrations that will inhibit growth results in substantially decreased accumulation of silver. Growth yield in chemostat culture is diminished in the presence of added Ag+, but this effect is moderated by added Cu2+, which may protect copper sites from Ag+ or compete with Ag+ for other sites at which Ag+ exerts toxic effects. Very small amounts of Cu2+ are found in cell samples from the chemostat compared to the substantial amounts of Ag+ taken up, but uptake of Cu2+ is decreased at higher [Ag+]/[Cu2+]ratios.
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Ghandour, W., Hubbard, J.A., Deistung, J. et al. The uptake of silver ions by Escherichia coli K12: toxic effects and interaction with copper ions. Appl Microbiol Biotechnol 28, 559–565 (1988). https://doi.org/10.1007/BF00250412
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DOI: https://doi.org/10.1007/BF00250412