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

Amer-lux bioreporter was constructed to assess the bioavailability of methylmercury [CH3 Hg(II)] inEscherichia coli . The bioreporter was shown to be sensitive, with a detection limit of 2.5 nM CH3 Hg(II), and was used to investigate the effects of chlorides, humic acids, and thiols on the bioavailability of CH3 Hg(II) inE. coli . It was found that increasing the concentration of chlorides resulted in an increase in CH3 Hg(II) bioavailability, suggesting that there was passive diffusion of the neutral complex (CH3 HgCl0 ). Humic acids were found to reduce the bioavailability of CH3 Hg(II) in varying degrees. Complexation with cysteine resulted in increased bioavailability of CH3 Hg(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 CH3 Hg(II) decreased with increasing glutathione concentrations.