title: Fractionation of Mercury Stable Isotopes during Microbial Methylmercury Production by Iron- and Sulfate-Reducing Bacteria.
abstract: The biological production of monomethylmercury (MeHg) in soils and sediments is an important factor controlling mercury (Hg) accumulation in aquatic and terrestrial food webs. In this study we examined the fractionation of Hg stable isotopes during Hg methylation in nongrowing cultures of the anaerobic bacteria Geobacter sulfurreducens PCA and Desulfovibrio desulfuricans ND132. Both organisms showed mass-dependent, but no mass-independent fractionation of Hg stable isotopes during Hg methylation. Despite differences in methylation rates, the two bacteria had similar Hg fractionation factors (αr/p = 1.0009 and 1.0011, respectively). Unexpectedly, δ(202)Hg values of MeHg for both organisms were 0.4‰ higher than the value of initial inorganic Hg after about 35% of inorganic Hg had been methylated. These results indicate that a (202)Hg-enriched pool of inorganic Hg was preferentially utilized as a substrate for methylation by these organisms, but that multiple intra- and/or extracellular pools supplied inorganic Hg for biological methylation. Understanding the controls of the Hg stable isotopic composition of microbially produced MeHg is important to identifying bioavailable Hg in natural systems and the interpretation of Hg stable isotopes in aquatic food webs.
authors.affiliation: Department of Environmental Sciences, Rutgers University , 14 College Farm Road, New Brunswick, New Jersey 08901, United States.
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Janssen
authors.affiliation: Department of Environmental Sciences, Rutgers University , 14 College Farm Road, New Brunswick, New Jersey 08901, United States.
authors.forename: Jeffra K
authors.initials: JK
authors.lastname: Schaefer
authors.affiliation: Department of Biochemistry and Microbiology, Rutgers University , 76 Lipman Drive, New Brunswick, New Jersey 08901, United States.
authors.forename: Tamar
authors.initials: T
authors.lastname: Barkay
authors.affiliation: Department of Environmental Sciences, Rutgers University , 14 College Farm Road, New Brunswick, New Jersey 08901, United States.
authors.forename: John R
authors.initials: JR
authors.lastname: Reinfelder
mesh_terms: D007501:Iron; D008628:Mercury; D008629:Mercury Isotopes; D008745:Methylation; D008767:Methylmercury Compounds; D013431:Sulfates; D014874:Water Pollutants, Chemical
chemical_list: D008629:Mercury Isotopes; D008767:Methylmercury Compounds; D013431:Sulfates; D014874:Water Pollutants, Chemical; D007501:Iron; D008628:Mercury