The biomineralization of metals by microorganisms in organic sediments

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Microorganisms drive key processes controlling the mobility of metals that are contained in minerals, adsorbed to organic and inorganic substrates, and dissolved in water at the Earth's surface. My research program centers on explaining how microbes common in Earth surface environments impact metal mobility by controlling electron transfer reactions through respiration; some microbes can use metals as electron donors and terminal electron acceptors. Changes to the oxidation state of some metals as a consequence of respiration can drastically impact their solubility. Biominerals result when such processes result in metal-rich precipitates. It is unknown how the microbial respiration of metals contributes to metal cycling in cold, northern peat wetlands. This is an important knowledge gap applicable to all peatlands, but I have chosen to focus on areas impacted by mining activities because: 1) the elevated concentrations of target elements provide a unique setting to understand metal biogeochemistry; 2) the capacity of wetlands to buffer metal releases to water systems is poorly understood; 3) the environmental impacts of some chemical discharges can be devastating to ecosystem health. Future climate warming and more extreme fluctuations in hydric regimes can be expected to affect microbial processes by altering microbial respiration, and by impacting the solubility of biominerals. This research is targeted at understanding a) the impacts of redox fluctuations induced by microbial respiration and oxygen exposure on the interactions between organic matter, iron and important target elements associated with some mines in northern Canada (U, Cr); b) the critical factors controlled by microbes and related to climate that impact biomineralization of target metals in peat substrates, and c) the capacity of native peat wetland systems to buffer metal fluxes during climate fluctuations. Addressing these objectives requires an interdisciplinary approach grounded in both geochemistry and microbiology. Projects to achieve the objectives include: 1) The dynamic relationship between iron oxide, organic matter, and U or Cr during cycles of reducing and oxidizing conditions created by microbial respiration, using batch systems; 2) Biomineralization of U, Cr, and Fe in a peat wetland substrate using flow cells, during changes in temperature and water saturation; 3) Changes in microbial community structure during simulated climate fluctuations in the flow cell system, in the presence of U, Cr and Fe; 4) The links between metal budgets in native, in situ peatlands during wet, cold conditions (spring) and warm, dry conditions (early fall); 5) Seasonal impacts on microbial communities and the correlation of specific microbial groups with metal dynamics in native peatlands. The research program will provide important training in laboratory and field techniques for graduate and undergraduate students. Students will be trained to use a multidisciplinary range of approaches that encompass observational and analytical scales that range from molecular to macroscopic. Developing novel experimental methods, such as X-ray absorption spectroscopy and analytical metal chemistry techniques, will provide important training, and will contribute critically to meeting the objectives of my research program. The outcome will be new fundamental knowledge on the dynamics of metal-microbe interactions in organic wetlands.