Phytoremediation of methylmercury pollution: merB expression in Arabidopsis thaliana confers resistance to organomercurials

Methylmercury is an environmental toxicant that biomagnifies and causes sev ere neurological degeneration in animals. It is produced by bacteria in soi ls and sediments that have been contaminated with mercury. To explore the p otential of plants to extract and detoxify this chemical, we engineered a m odel plant, Arabidopsis thaliana, to express a modified bacterial gene, mer Bpe, encoding organomercurial lyase (MerB) under control of a plant promote r. MerB catalyzes the protonolysis of the carbon-mercury bond, removing the organic ligand and releasing Hg(II), a less mobile mercury species. Transg enic plants expressing merBpe grew vigorously on a wide range of concentrat ions of monomethylmercuric chloride and phenylmercuric acetate. Plants lack ing the merBpe gene were severely inhibited or died at the same organomercu rial concentrations. Six independently isolated transgenic lines produced m erBpe mRNA and MerB protein at levels that varied over a 10- to 15-fold ran ge, and even the lowest levels of merBpe expression conferred resistance to organomercurials. Our work suggests that native macrophytes (e.g,, trees, shrubs, grasses) engineered to express merBpe may be used to degrade methyl mercury at polluted sites and sequester Hg(II) for later removal.