Biogeochemical cycling of mercury in terrestrial environments: Emphasis on mercury uptake by black spruce (Picea mariana) in peatlands and impacts of invasive earthworms on soil mercury cycling

University of Minnesota M.S. thesis. June 2015. Major: Land and Atmospheric Science. Advisor: Edward Nater. 1 computer file (PDF); xiii, 142 pages.Mercury (Hg) is a naturally occurring element but has become an important environmental pollutant mostly due to human activities. This thesis focuses on deposition of mercury to terrestrial environments where vegetation and soil act as important sinks of mercury. The first study, focuses on the uptake of elemental mercury by black spruce trees in peatland environments to assess their potential ability to be used as passive atmospheric biomonitors. The second study, focuses on the impacts of invasive earthworms to mercury cycling in the soil. Earthworms feed primarily on organic rich forest floor which coincidentally complexes the largest amounts of mercury. Heavy earthworm invasions result in the complete consumption of the forest floor, which likely alters mercury cycling in forest soils. Two mass balance approaches are used to assess the mercury dynamics of these soils

Toward Bioremediation of Methylmercury Using Silica Encapsulated Escherichia coli Harboring the mer Operon.

Mercury is a highly toxic heavy metal and the ability of the neurotoxin methylmercury to biomagnify in the food chain is a serious concern for both public and environmental health globally. Because thousands of tons of mercury are released into the environment each year, remediation strategies are urgently needed and prompted this study. To facilitate remediation of both organic and inorganic forms of mercury, Escherichia coli was engineered to harbor a subset of genes (merRTPAB) from the mercury resistance operon. Protein products of the mer operon enable transport of mercury into the cell, cleavage of organic C-Hg bonds, and subsequent reduction of ionic mercury to the less toxic elemental form, Hg(0). E. coli containing merRTPAB was then encapsulated in silica beads resulting in a biological-based filtration material. Performing encapsulation in aerated mineral oil yielded silica beads that were smooth, spherical, and similar in diameter. Following encapsulation, E. coli containing merRTPAB retained the ability to degrade methylmercury and performed similarly to non-encapsulated cells. Due to the versatility of both the engineered mercury resistant strain and silica bead technology, this study provides a strong foundation for use of the resulting biological-based filtration material for methylmercury remediation

Scanning Electron Microscopy images of encapsulation silica sol-gel microbeads containing <i>E</i>. <i>coli</i> pBBRBB::<i>mer</i>.

<p>A) Representative image depicting the smooth, spherical shape of silica microbeads following encapsulation in aerated mineral oil. Scale bar represents 200 μm B) Image of engineered <i>E</i>. <i>coli</i> pBBRBB::<i>mer</i> cells within encapsulation beads. Scale bar represents 5 μm.</p