HR: 0800h
AN: B11B-0409    [Abstracts]
TI: Complexation of Inorganic Mercury by Cysteine Promotes Bacterial Methylation of Mercury
AU: * Schaefer, J K
EM: jschaefe@princeton.edu
AF: Geosciences, Princeton University, Guyot Hall, Princeton, NJ 08544,
AU: Walsh, M J
EM: mjw66@cornell.edu
AF: Biological and Environmental Engineering, Cornell University, 320 Riley-Robb Hall, Ithaca, NY 14853,
AU: Ahner, B A
EM: baa7@cornell.edu
AF: Biological and Environmental Engineering, Cornell University, 320 Riley-Robb Hall, Ithaca, NY 14853,
AU: Morel, F M
EM: morel@princeton.edu
AF: Geosciences, Princeton University, Guyot Hall, Princeton, NJ 08544,
AB: One critical factor controlling methylmercury (MeHg) accumulation in the environment is the chemical form of Hg(II) available for methylation by bacteria. Current models suggest that passive diffusion of neutral sulfide complexes may determine the bioavailability and methylation of mercury; however, these hypotheses have never been thoroughly tested. We have investigated how the chemical speciation of Hg(II) affects mercury methylation in washed cell suspensions of the Hg(II)-methylating bacterium, Geobacter sulfurreducens. In assays where the dominant Hg-binding ligand is either chloride or sulfide, MeHg is produced at a rate of about 10^-21 mol MeHg/h/cell, with 1-5% of the total Hg(II) (HgT = 5 nM) being eventually methylated. The binding of Hg to cysteine greatly accelerates MeHg formation with near complete methylation of the added Hg(II). MeHg formation is directly proportional to the concentration of Hg-cysteine complex and can be reduced by increasing the proportion of Hg- chloride or Hg-sulfide species. The addition of Cu(II) results in a large reduction in the methylation of Hg(II) presumably as the result of the chemical oxidation of cysteine. Exudates released by G. sulfurreducens during growth appear to enhance mercury methylation in washed cell suspensions relative to control assays. This response is likely due to the release of cysteine or other thiols into the bulk medium during growth. The results of this study suggest a need to reevaluate our models for mercury uptake and methylation in anaerobic bacteria to include the importance of small molecular weight thiols in controlling methylmercury formation.
DE: 0409 Bioavailability: chemical speciation and complexation
DE: 0448 Geomicrobiology
DE: 0461 Metals
SC: Biogeosciences [B]
MN: 2007 Fall Meeting