Extremophiles in Polar Regions (e.g., Mercury resistant bacteria in Arctic snow)
Far from inert, seasonal Arctic snowpacks are chemically dynamic and interact with different environmental compartments such as the atmosphere, soil and meltwater-fed ecosystems. Due to the cold conditions and the limited supply of liquid water, snow and ice have long been considered as no more than entrapment and storage systems for microorganisms (Cowan and Tow, 2004). However, this view started to change after studies that examine the impact of microorganisms on the dynamics of nutrients (Hodson et al., 2008) , on their role in shifting surface albedo of snow (Thomas and Duval, 1995) and on hydrochemistry (Tranter et al., 2002) . Microorganisms also impact the transformation of contaminants, such as Hg (Poulain et al., 2007) through detoxification processes that convert inorganic Hg to Hg° and methylation/demethylation processes that convert inorganic Hg to MeHg and vice versa (Barkay et al., 2003). In turn, chemistry can impact the microbial community structure in different environments. In field and laboratory studies, Duran et al. (2008) determined that Hg contributes to altering community structure and function with the enrichment of resistant populations and changes in contaminant metabolism in sediments. However, the dynamics of change in complex systems remain to be examined. A recent report on a seasonal Arctic snowpack showed that the chemical environment evolves rapidly along a seasonal gradient and that Hg transformations were occurring within (Larose et al., 2010b). We also showed that the seasonal snowpack supports a variety of microbial populations that vary through the season (Amato et al., 2007, Larose et al., 2010a) . If the chemistry of the snowpack is dynamic and if life is sustainable in this type of environment, then it is likely that the communities inhabiting this system are as well.
Larose, C., Dommergue, A., De Angelis, M., Cossa, D., Averty, B., Marusczak, N., Soumis, N., Schneider, D., and Ferrari, C.: 2011. Springtime changes in snow chemistry lead to new insights into mercury methylation in the arctic, Geochim. Cosmochim.Acta, in Press.
Larose, C., Sibel Berger, Christophe Ferrari, Elisabeth Navarro, Aurélien Dommergue, Dominique Schneider, Vogel, T.M. 2010. Microbial sequences retrieved from environmental samples from seasonal Arctic snow and meltwater from Svalbard, Norway. Extremophiles.14:205-12.
Dommergue A, Larose C, Faïn X, Clarisse O, Foucher D, Hintelmann H, Schneider D, Ferrari CP. 2010. Deposition of mercury species in the Ny-Alesund area (79 degrees N) and their transfer during snowmelt. Environ Sci Technol. 44:901-7.