Applied Microbiology and Biotechnology

, Volume 28, Issue 6, pp 559–565 | Cite as

The uptake of silver ions by Escherichia coli K12: toxic effects and interaction with copper ions

  • Wala Ghandour
  • Julia A. Hubbard
  • Janet Deistung
  • Martin N. Hughes
  • Robert K. Poole
Biotechnology

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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Copyright information

© Springer-Verlag 1988

Authors and Affiliations

  • Wala Ghandour
    • 1
  • Julia A. Hubbard
    • 1
    • 2
  • Janet Deistung
    • 1
  • Martin N. Hughes
    • 1
  • Robert K. Poole
    • 2
  1. 1.Department of ChemistryKing's College LondonLondonU.K.
  2. 2.Department of MicrobiologyKing's College LondonLondonU.K.

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