title: Species-specific stable isotope fractionation of mercury during Hg(II) methylation by an anaerobic bacteria (Desulfobulbus propionicus) under dark conditions.
abstract: This work reports the first results on the stable isotope fractionation of Hg during methylation by anaerobic bacteria under dark conditions. The GC-MC-ICPMS methodology employed is capable of simultaneously measuring the species-specific isotopic composition of different Hg species within the same sample. We have studied Hg isotopic fractionation caused by methylation of Hg(II) standard reference material NIST-3133 in the presence of the pure bacterial strain Desulfobulbus propionicus MUD10 (DSM 6523) under fermentative conditions. We have measured the isotopic composition of Hg(II) and monomethyl mercury (MMHg) in these cultures as a function of time and calculated delta-values for both species versus the starting material (NIST-3133) as a delta-zero standard. Two different strategies for the incubation were applied: single sampling cultures and a continuous sampling culture. The results obtained have shown that under the conditions employed in this work the methylation of Hg(II) causes mass-dependent fractionation of the Hg isotopes for both Hg(II) substrate and produced MMHg. Such a process occurred under the exponential growth of the bacteria which preferentially methylate the lighter isotopes of Hg. After 96 h for the continuous culture and 140 h for the single sampling cultures, we observed a change in the fractionation trend in the samples at a similar cell density value (ca. 6.0 x 10(7) cells mL(-1)) which suggests the increasing contribution of a simultaneous process balancing methylation extent such as demethylation. Assuming that Rayleigh type fractionation conditions are met before such suppression, we have obtained a alpha(202/198) fractionation factor of 1.0026 +/- 0.0004 for the single sampling cultures.
authors.affiliation: Laboratoire de Chimie Analytique Bio-Inorganique et Environnement, and Equipe Environnement et Microbiologie, Institut Pluridisciplinaire de Recherche sur l'Environnement et les Matériaux, Université de Pau et des Pays de l'Adour, UMR CNRS- 5254-IPREM, 2 Avenue Pierre Angot, 64053 Pau, France. rodriguezpablo@uniovi.es
authors.forename: Pablo
authors.initials: P
authors.lastname: Rodríguez-González
authors.forename: Vladimir N
authors.initials: VN
authors.lastname: Epov
authors.forename: Romain
authors.initials: R
authors.lastname: Bridou
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Tessier
authors.forename: Remy
authors.initials: R
authors.lastname: Guyoneaud
authors.forename: Mathilde
authors.initials: M
authors.lastname: Monperrus
authors.forename: David
authors.initials: D
authors.lastname: Amouroux
mesh_terms: D005591:Chemical Fractionation / Q000379:methods*; D003624:Darkness; D020564:Deltaproteobacteria / Q000378:metabolism*; D008629:Mercury Isotopes / Q000737:chemistry*; D008745:Methylation
chemical_list: D008629:Mercury Isotopes