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首页> 外文期刊>Environmental Science & Technology: ES&T >Competitive binding of Cu2+ and Zn2+ to live cells of Shewanella putrefaciens
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Competitive binding of Cu2+ and Zn2+ to live cells of Shewanella putrefaciens

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摘要

Binding of Cu2+ and Zn2+ to live cells of Shewanella putrefaciens was measured at pH 4, 5.5, and 7 for dissolved metal concentrations ranging from 0.1 to 100 mu M. Release of organic compounds by the cells resulted in concentrations of dissolved organic carbon (DOC) between 0.5 and 1.6 mM. A discrete site, none lectrostatic model was used to describe Cu2+ and Zn2+ binding to the cells. Binding of Zn2+, which increased with increasing pH over the entire range of dissolved Zn2+ concentration, could be explained by invoking two types of cell wall binding sites: acidic and neutral functional groups. Binding of Cu2+ exhibited a more complex pH dependence: at dissolved metal concentrations below 1 mu M, binding to the cells actually increased with decreasing pH. This behavior could be reproduced by (1) assuming the existence of a small fraction of high-affinity binding sites in the cell wall (similar to 5) and (2) including metal complexation by dissolved organic ligands. The latter compete with the neutral cell wall groups and decrease Zn2+ and Cu2+ binding at pH 5.5 and 7. The observed isotherms implied that binding of the metals was only weakly affected by cell wall charging. Model parameters derived from the single-metal binding isotherms were able to account for the observed competition of Zn2+ and Cu2+ for cell wall sites when both metals were present.

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