Science at the Edge

Friday January 31, 2020

 

11:30 a.m., Room 1400 Biomedical and Physical Sciences Building

Refreshments served at 11:00 a.m.

 

 

Eric Roden from the University of Wisconsin

 

 

Making extracellular contact: outer membrane protein mediated iron redox cycling in soils and sediments”

 

Iron (Fe) bearing oxide, sulfide, and silicate minerals are important components of natural soils, sediments, and aquifers, i.e. the subsurface realm of the critical zone (Earth’s permeable near surface layer, from the tops of the trees to the bottom of actively cycling groundwater). Such phases engage in redox reactions with inorganic and organic compounds that impact a wide variety of geological and environmental process, such as sediment diagenesis, chemical weathering, and the mobility and fate of organic and inorganic contaminants. Because Fe-bearing minerals are typically highly insoluble in circumneutral pH, near-surface environments, their redox transformation takes place by way of chemical reactions at the mineral-water interface. In the case of microbially-mediated pathways, these redox reactions rely on processes external to the cell surface, which are referred to collectively as “extracellular electron transfer” (EET). Reductive EET pathways have been studied extensively in the context of microorganisms that couple heterotrophic metabolism to dissimilatory reduction of Fe(III) oxides and other Fe(III)-bearing mineral phases. Less is known about oxidative EET pathways, particularly in relation to weathering of insoluble Fe(II)-bearing sulfide and silicate phases. This presentation will bring together prior studies that illustrate how EET pathways can link reductive and oxidative transformations of Fe in near-surface environments, and our more recent work that combines in situ geochemistry, microbiological experimentation, and genomic sequencing to reveal previously unrecognized pathways whereby microbial EET may accelerate oxidative weathering of insoluble Fe(II)-bearing mineral phases.