The effect of chelated and soil-adsorbed copper on whole-cell soluble methane monooxygenase activity in Methylosinus trichosporium OB3b was measured to assess the bioavailability of these forms of copper. Strongly binding chelating agents (Log K > 16) added to the growth medium at a concentration of 20 μM were able to reduce copper bioavailability. As these chelating agents limited equilibrium binding of copper by cell-produced copper binding ligands and limited accumulation by passive uptake mechanisms, it appears the ability of the cells' copper uptake system to sequester copper in a bioavailable form is compromised by these competing ligands. Copper sorbed as surface complexes on montmorillonite clay,γ-alumina, ferrihydrite, and goethite were bioavailable. However, with increasing concentration of surface sites, bioavailability decreased, indicating the competitive advantage for copper binding provided by high concentrations of binding sites limited the ability of the cells' copper uptake system to accumulate copper in a bioavailable form. Such information on the bioavailability of copper can enhance the utility of methanotrophs for in situ biodegradation of priority pollutants. As these cells' ability to degrade chlorinated solvents changes dramatically with varying copper bioavailability, these studies provide data that can be used to optimize methanotrophic mediated bioremediation efforts.
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