Microbial controls of mercury cycling

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Major environmental changes now underway combined with increased exploitation of northern natural resources impose an important stress on ecosystems, namely by altering the fate of contaminants. To ensure sound management of these resources and protection of wildlife and human health, it is critical to further our ability to predict the fate of toxicants and to develop remediation strategies in typical Canadian landscapes and conditions. Among toxic metals, mercury (Hg) is a global priority contaminant due to the biomagnification of its most toxic form monomethylmercury (MMHg) in foodwebs, even in remote regions such as the Canadian Arctic. The importance of Hg as a chemical of major concern to human health was underscored by the recent adoption of the Minamata Convention on Mercury, a legally binding treaty signed in Oct 2013 by more than 140 countries including Canada. This treaty requires that government agencies be equipped to monitor processes affecting global Hg transport and cycling. This proposal will fill important gaps of knowledge related to Hg transport and cycling highlighted in the most recent UN Environmental Programme Hg assessment report. My first objective is to determine how dissolved organic matter (DOM) affects Hg and MMHg bioavailability to assess the link between Hg deposition, methylation and uptake by living organisms. My second objective is to characterize the diversity of Hg resistance strategies in cold-adapted microbes and develop new microbe-based ecosystem services for the bioremediation of contaminated sites. My third objective aims to develop new paleo-proxies that track Hg remobilization in the environment by evaluating how genetically encoded bacterial resistance mechanisms evolved in response to recent changes in Hg delivery to ecosystems. This last objective will contribute to evaluating the time lag involved in ecosystem responses to mercury deposition and predicting recovery time following the reduction in Hg emissions.