Some like it cold: microbial transformations of mercury in polar regions

Figures & data

Fig. 1  The biogeochemical cycle of mercury in coastal marine environments in polar regions. Major reaction and transport pathways, provided as numbers in parentheses in the figure, are: (1) atmospheric oxidation of Hg(0) to Hg(II); (2) photoreduction of newly deposited Hg(II) to Hg(0); (3) biological reduction of Hg(II) to Hg(0); (4) evasion of Hg(0) to the atmosphere; (5) methylation of Hg(II) to CH₃Hg by sulfate-reducing bacteria (SRB) and iron-reducing bacteria (FeRB); (6) methylation of Hg(II) to CH₃Hg by aerobic pathway and/or by photomethylation in snow; (7) methylation of Hg(II) to CH₃Hg by algae and phytoplankton in the water column; (8) photochemical degradation of diMeHg in the atmosphere; (9) biological demethylation of CH₃Hg to Hg(II); and (10) photochemical demethylation of CH₃Hg in snow. Methylation pathways are highlighted by bold lettering. Note that these reactions and pathways may take place in various compartments of polar regions; for the sake of simplicity they are only marked in a representative compartment in the figure (see text for details). Dimethylsulfoniopropionate is abbreviated to DMSP, dimethylsulfide to DMS and methylsulfonic acid to MSA.

Fig. 2  The number of papers retrieved on 11 October 2010 from the ISI Web of Knowledge database, using the keywords indicated. The search was performed using Boolean operators to avoid references to unrelated topics. The descriptor “microbes” is used for clarity and is based on a search that was performed using the query Microbes OR Bacteria OR Archaea AND all other terms as indicated in the figure.

Table 1 A summary of the uniqueness of microbial transformations and research questions whose answers would enhance our understanding of Hg biogeochemistry in polar regions.

Microbial transformation	What is unique about this transformation in polar regions	Questions/research needs
Methylation	Presence of diMeHg in coastal water (Pongratz & Heumann 1999; Kirk et al. 2008) Snow as a matrix for Hg transformations and MeHg transport (Constant et al. 2007). Marine sources for MeHg deposition in coastal regions (St. Louis et al. 2005; Larose, Dommergue et al. 2010)	What are the pathways for methylation and what fraction of the deposited Hg is being methylated? What are the pathways for aerobic Hg methylation? Who methylates Hg in polar regions? What is the effect of permafrost thawing on methylation rate and subsequent input of MeHg to polar regions?
Demethylation	Oxidation of C1 compounds is slow in high latitudes (Hines & Duddleston 2001) mer gene expression in Arctic biomass (Poulain, Ni Chadhain et al. 2007) Photoreduction of MeHg in epilimnetic lake water (Hammerschmidt & Fitzgerald 2006)	What are the pathways for the degradation of MeHg in polar regions?
Hg(II) reduction	Accumulation of dissolved gaseous Hg under sea ice (Andersson et al. 2008) Hg-resistant bacteria are common in snowpacks (Møller et al. 2011) High bioavailability of Hg(II) in freshly deposited snow (Lindberg et al. 2002), Barkay & Kroer (unpubl. data) Interactions of microbes with Hg in structured environments mer gene expression in Arctic biomass (Poulain, Ni Chadhain et al. 2007) and its impact on Hg(II) reduction	Development of psychrophilic Hg biosensors The interactions of microbes in sea ice with Hg; role of exopolysaccharide production Measurement of Hg concentrations in the complex sea ice matrix Further assess the evolution of Hg resistance in polar areas
Hg(0) oxidation	High chloride concentrations in coastal marine environments induce abiotic oxidation of Hg(0)	A better understanding of Hg(0) oxidation in Hg biogeochemistry

Poulain A.J. Garcia E. Amyot M. Campbell P.G.C. Arlya P.A. Mercury distribution, partitioning and speciation in coastal vs. inland High Arctic snow. Geochimica et Cosmochimica Acta. 2007; 71: 3419–3431.

 Web of Science ®Google Scholar