Microbial communities and activity in peatlands

Peat wetlands cover much of our boreal and arctic landscape, sequestering a large proportion of the world's soil carbon. The microbes in these habitats breakdown organic matter slowly to methane and carbon dioxide, releasing these greenhouse gases to the atmosphere. High latitude environments are currently undergoing significant warming trends and melting of permafrost from the impacts of global climate change. These changes are having profound effects on these wetlands, promoting the transition from nutrient-poor bogs to richer fens. Our research is examining the influence the wetland trophic status has on the microbial populations and the metabolic pathways observed.  How these processes influence microbial communities and their activity is an important area of research in order to predict future trends.

​Publications:
J. L. Wilmoth, J. K. Schaefer, D. R. Schlesinger, S. Roth*, P. G. Hatcher, J. K. Shoemaker, and X. Zhang. 2021. The role of oxygen in stimulating methane production in wetlands. Global Change Biology. onlinelibrary.wiley.com/doi/full/10.1111/gcb.15831

Microbial production of methylmercury in northern wetlands

Mercury is a global priority pollutant affecting large numbers of ecosystems and populations around the world. Mercury is emitted to the atmosphere largely from the combustion of fossil fuels, especially coal-fired power plants. Once in the atmosphere, mercury can travel significant distances before being deposited back to land in rain and snow, often to environments remote from industrial pollution. Microorganisms can transform mercury in many ways, the most troubling of which is the biological conversion of inorganic Hg(II) to the organic form, methylmercury. Methylmercury is a potent neuromuscular toxin which bioaccumulates and biomagnifies in food webs, posing health risks to end-consumers, including humans. Wetlands are known "hot spots" for methylmercury production as the absence of oxygen and abundance of organic matter create ideal habitats for these mercury methylating microbes. Our research is focused on understanding important links between wetland type, microbial populations, microbial activity and methylmercury accumulation. This research will improve our understanding of the critical microbial and biogeochemical controls promoting methylmercury cycling in these wetlands. This current project is in collaboration with Tamar Barkay (Rutgers University), Mark Hines (University of Massachusetts, Amherst), David Krabbenhoft (US Geological Survey, Madison, WI), and Brett Poulin (US Geological Survey, Boulder, CO). Previous projects were conducted in boreal wetlands of Sweden in collaboration with Ulf Skyllberg (SLU, Sweden) and Erik Björn (Ümea University, Sweden).

Publications:
S. Roth, B. Poulin, Z. Baumann, X. Liu, L. Zhang, D. Krabbenhoft, M. E. Hines, J. K. Schaefer, and T. Barkay. 2021. Nutrient inputs stimulate mercury methylation by syntrophs in a subarctic peatland. Frontiers of Microbiology. In Press.
Schaefer, J. K., R. M. Kronberg, E. Björn, U. Skyllberg. 2020. Anaerobic guilds responsible for mercury methylation in boreal wetlands of varied trophic status serving as either a methylmercury source or sink. Environ. Microbiol.  doi.org/10.1111/1462-2920.15134 
B. A. Poulin, J. N. Ryan, M. T Tate, D. P. Krabbenhoft, M. E. Hines, T. Barkay, J. K. Schaefer, and G. R. Aiken. 2019. Geochemical factors controlling dissolved elemental mercury and methylmercury formation in Alaskan wetlands of varying trophic status. Environ. Sci. Technol. 53:6203-6213, doi: 10.1021/acs.est.8b06041.
R.-M. Kronberg, J. K. Schaefer, E. Björn, and U. Skyllberg. 2018. Mechanisms of methyl mercury net degradation in alder swamps: the role of methanogens and abiotic processes. Environ. Sci. Technol. Lett. 5(4): 220-225​.
J. K. Schaefer, R.-M. Kronberg, F. M. M. Morel, U. Skyllberg. 2014. Detection of a key Hg methylation gene, hgcA, in wetland soil. Environ. Microbiol. Rep. 6: 441-447.

Mercury bioavailability and uptake in mercury methylating microorganisms

The uptake and internalization of inorganic mercury(II) is a critical step in determining the amount of methylmercury that is formed. In collaboration with Erik Björn (Ümea University, Sweden) and Ulf Skyllberg (SLU, Sweden), we are examining the mechanisms of mercury uptake and methylation in organisms which produce the neurotoxin, methylmercury. Funding is provided by the Swedish Research Council Formas.

Publications:
G. A. Adediran, V Liem-Nguyen, Y. Song, J. K. Schaefer, U. Skyllberg, E. Björn. Microbial biosynthesis of thiol compounds: implications for speciation, cellular uptake and methylation of Hg(II). Environ. Sci. Technol. doi.org/10.1021/acs.est.9b01502
A. Szczuka, F. M. M. Morel, and J. K. Schaefer. 2015. The effect of thiols, zinc, and redox conditions on Hg uptake in Shewanella oneidensis. Environ. Sci. Technol. 49: 7432-7438.
J. K. Schaefer, A. Szczuka, and F. M. M. Morel. 2014. Effect of divalent metals on Hg(II) uptake and methylation by bacteria. Environ. Sci. Technol. 48: 3007-3013.
J. K. Schaefer, S. S. Rocks, W. Zheng, L. Liang, B. Gu, and F. M. Morel. 2011. Active transport, substrate specificity, and methylation of Hg(II) in anaerobic bacteria. Proc. Nat. Acad. Sci. 108: 8714-8719.
J. K. Schaefer, and F. M. M. Morel. 2009. High methylation rates of mercury bound to cysteine by Geobacter sulfurreducens. Nature Geosci. 2: 123-126.

Copper homeostasis in strict anaerobic microorganisms

Copper is an essential trace metal for many organisms; however, it can be toxic at elevated concentrations. Little is known about how organisms deal with copper(I) exposure under conditions where the reduced form of copper accumulates.  Our research is focused on understanding the mechanism of copper homeostasis in a strict anaerobic organism, the iron-reducing bacterium, Geobacter sulfurreducens -- a microbe ubiquitous in surface and subsurface environments including many contaminated with heavy metals such as uranium, mercury, and copper.

Metal contamination in the Raritan River, NJ

The Raritan River in New Jersey has a long history of industrial activity resulting in considerable contamination of numerous organic and heavy metal pollutants. In collaboration with Kaixuan Bu (Marine Sciences, Rutgers) and students in the Analytical Environmental Chemistry Lab (11:375:310), we are examining the distribution of toxic metals (copper, lead, chromium, cadmium, arsenic, mercury) in the surface water, sediment, and plankton within the tidal portion of the lower Raritan River.  This project was partially funded by the Raritan River Consortium Minigrant program. The pictures below show Environmental Science undergraduates in Analytical Environmental Chemistry Lab collecting water, biomass, and sediment in our April boat cruise on-board the R/V Rutgers.