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 hydroperoxidase-catalase, KatG, of Escherichia coli can oxidize monatomic elemental mercury vapor, Hg(0), to the water-soluble, ionic form, Hg(II). A strain with a mutation in katG and a strain overproducing KatG were used to demonstrate that the amount of Hg(II) formed is proportional to the catalase activity. Hg(0) oxidation was much decreased in stationary-phase cells of a strain lacking KatG, suggesting that the monofunctional hydroperoxidase 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 this reaction. Two typical soil bacteria, Bacillus and Streptomyces, also oxidize Hg(0) to Hg(II). These observations establish for the first time that bacteria can contribute, as do mammals and plants, to the oxidative phase of the global Hg cycle.

本研究采用金属调控型荧光素酶报告基因融合体（metalloregulated luciferase reporter fusions）与可溶性Hg(II)的光谱定量分析技术，证实大肠杆菌（Escherichia coli）的过氧化物酶-过氧化氢酶KatG（hydroperoxidase-catalase, KatG）可将单原子元素汞蒸气（Hg(0)）氧化为水溶性离子态汞（Hg(II)）。通过构建katG基因突变菌株与KatG过表达菌株，本研究证实生成的Hg(II)产量与过氧化氢酶活性呈正相关。在缺失KatG的菌株的稳定期细胞（stationary-phase cells）中，Hg(0)氧化活性显著降低，提示单功能过氧化物酶KatE（monofunctional hydroperoxidase KatE）在此反应中的催化效率更低。出乎意料的是，在同时缺失KatE与KatG的菌株中仍可检测到Hg(0)氧化活性，这表明除过氧化物酶外，其他酶促活性也可催化该反应。两种典型土壤细菌——芽孢杆菌属（Bacillus）与链霉菌属（Streptomyces）——同样可将Hg(0)氧化为Hg(II)。上述实验结果首次证实，与哺乳动物和植物一样，细菌也可参与全球汞循环（global Hg cycle）的氧化阶段。