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Applied and Environmental Microbiology, April 2007, p. 2230-2238, Vol. 73, No. 7
0099-2240/07/$08.00+0     doi:10.1128/AEM.02701-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Potential for Mercury Reduction by Microbes in the High Arctic

Groupe de Recherche Inter-universitaire en Limnologie (GRIL), Département des Sciences Biologiques, Université de Montréal, C. P. 6128, Succursale Centre-Ville, Pavillon Marie-Victorin, Montréal, Québec, Canada H3C 3J7,¹ Biotechnology Center for Agriculture and the Environment, Cook College, Rutgers University, Foran Hall, 59 Dudley Road, New Brunswick, New Jersey 08901-8520,² Department of Chemistry and Atmospheric and Oceanic Sciences, McGill University, 801 Sherbrooke Street West, Montréal, Quebec, Canada H3A 2K6,³ Université du Québec, INRS-Eau, Terre et Environnement, 490 de la Couronne, Québec, Canada G1K 9A9,⁴ Department of Biochemistry and Microbiology, Rutgers University, 76 Lipman Drive, New Brunswick, New Jersey 08901⁵

Received 19 November 2006/ Accepted 5 February 2007

The contamination of polar regions due to the global distribution of anthropogenic pollutants is of great concern because it leads to the bioaccumulation of toxic substances, methylmercury among them, in Arctic food chains. Here we present the first evidence that microbes in the high Arctic possess and express diverse merA genes, which specify the reduction of ionic mercury [Hg(II)] to the volatile elemental form [Hg(0)]. The sampled microbial biomass, collected from microbial mats in a coastal lagoon and from the surface of marine macroalgae, was comprised of bacteria that were most closely related to psychrophiles that had previously been described in polar environments. We used a kinetic redox model, taking into consideration photoredox reactions as well as mer-mediated reduction, to assess if the potential for Hg(II) reduction by Arctic microbes can affect the toxicity and environmental mobility of mercury in the high Arctic. Results suggested that mer-mediated Hg(II) reduction could account for most of the Hg(0) that is produced in high Arctic waters. At the surface, with only 5% metabolically active cells, up to 68% of the mercury pool was resolved by the model as biogenic Hg(0). At a greater depth, because of incident light attenuation, the significance of photoredox transformations declined and merA-mediated activity could account for up to 90% of Hg(0) production. These findings highlight the importance of microbial redox transformations in the biogeochemical cycling, and thus the toxicity and mobility, of mercury in polar regions.

Published ahead of print on 9 February 2007.