Effect of Inorganic and Organic Ligands on the Bioavailability of Methylmercury as Determined by Using a mer-lux Bioreporter

A mer-lux bioreporter was constructed to assess the bioavailability of methylmercury [CH3Hg(II)] in Escherichia coli. The bioreporter was shown to be sensitive, with a detection limit of 2.5 nM CH3Hg(II), and was used to investigate the effects of chlorides, humic acids, and thiols on the bioavailability of CH3Hg(II) in E. coli. It was found that increasing the concentration of chlorides resulted in an increase in CH3Hg(II) bioavailability, suggesting that there was passive diffusion of the neutral complex (CH3HgCl0). Humic acids were found to reduce the bioavailability of CH3Hg(II) in varying degrees. Complexation with cysteine resulted in increased bioavailability of CH3Hg(II), while assays with equivalent concentrations of methionine and leucine had little or no effect on bioavailability. The mechanism of uptake of the mercurial-cysteine complexes is likely not passive diffusion but could result from the activities of a cysteine transport system. The bioavailability of CH3Hg(II) decreased with increasing glutathione concentrations.