Colloquium: Ted Flynn

Theodore Flynn, Research Scientist,Computation Institute, University of Chicago, Bioscience Division, Argonne National Laboratory

Abstract:  The biogeochemical cycling of iron, sulfur, and carbon are inextricably linked in subsurface environments such as aquifers, and the chemical reactions that control the speciation and solubility of these elements are often controlled by microbial metabolism. Microorganisms such as metal reducers (i.e. Geobacter, Shewanella), sulfate reducers (i.e. Desulfobacter, Desulfobulbus), and methanogens (i.e Methanosarcina, Methanosaeta) respire anaerobically using ferric iron, elemental sulfur (S⁰), sulfate, and bicarbonate as electron acceptors and by so doing, these microbes exert strong control on the geochemistry of groundwater and aquifer sediments. The revolution in high-throughput DNA sequencing and the subsequent development of molecular geomicrobiology has brought about a drastic shift in our understanding of microbial environments in the subsurface. Rather than being dominated by a single, predominant group of microbes as was previously thought, metagenomic analyses commonly find diverse communities of different microorganisms regardless of how the groundwater is classified by geochemical criteria. These results indicate that electron flux in the subsurface is likely not a straightforward path through one particular functional group, but a complex network involving both biotic and abiotic pathways, including cryptic redox cycles such as anaerobic methane oxidation and sulfur-mediated electron shuttling.