BACTERIAL OXIDATION OF MERCURY METAL VAPOR, HG(0)

We used metalloregulated luciferase reporter fusions and spectroscopic quantification of soluble Hg(II) to determine that the hydroperoxidas e-catalase, KatG, of Escherichia coli can oxidize monatomic elemental mercury vapor, Hg(0), to the water-soluble, ionic form, Hg(II). A stra in with a mutation in katG and a strain overproducing KatG were used t o demonstrate that the amount of Hg(II) formed is proportional to the catalase activity. Hg(0) oxidation was much decreased in stationary-ph ase cells of a strain lacking KatG, suggesting that the monofunctional hydroperoxide KatE is less effective at this reaction. Unexpectedly, Hg(0) oxidation also occurred in a strain lacking both KatE and KatG, suggesting that activities other than hydroperoxidases may carry out t his reaction. Two typical soil bacteria, Bacillus and Streptomyces, al so oxidize Hg(0) to Hg(II). These observations establish for the first time that bacteria can contribute, as do mammals and plants, to the o xidative phase of the global Hg cycle.