AOM becomes energetically favorable in LS wells at concentrations of H2(aq) of less than roughly 0.2 nM (Additional file 1: Figure S3), which is 1–2 https://www.selleckchem.com/products/wnt-c59-c59.html orders of magnitude
less than the bulk concentration of H2 in groundwater. Depending upon the kinetics of H2 consumption, such a gradient would be feasible inside a biofilm [55]. Alternatively, recent studies BIBF 1120 have demonstrated direct electron transfer between cells without the intermediate formation of H2[60, 61]. If this occurs close cell contact would still be required for AOM to be feasible. Our study, however does not resolve whether such specific close cell associations occur in the Mahomet aquifer or whether these are specifically associated with AOM in this system. We hope to address this more fundamentally in a future study. The discovery of Mahomet Arc 1, which appears to be associated
with AOM, in a pristine aquifer suggests the anaerobic oxidation of methane may be an additional important metabolic pathway in this system. The heterogeneity of aquifer sediments also leads to numerous microenvironments whose redox chemistry can differ greatly from the bulk groundwater [62]. Molecular diffusion and advective transport can transport methane from the highly reduced zones where it is produced Selleckchem VX-680 into areas where it might be consumed through an AOM-mediating syntrophic partnership. Because the rates at which CH4 is produced and potentially consumed are difficult to quantify in situ, anaerobic methane oxidation is frequently overlooked in groundwater ecosystems [10]. The abundance of Mahomet Arc 1 sequences and their correlation triclocarban to the concentration
of sulfate then not only suggests the potential importance of AOM as a biogeochemical pathway in the Mahomet, but underscores the largely-untapped potential provided by molecular microbial ecology to better define redox processes in pristine aquifers. Conclusions While this study greatly increases our understanding of the microbial communities that catalyze the biogeochemical cycling of carbon and metals in the Mahomet aquifer, additional studies are needed to shed light on the dynamics of microbial activities of this and other subsurface systems over time. Moreover, molecular surveys represent an important foundation for studies trying to understand how changes in subsurface chemistry may impact subsurface communities exposed to anthropogenic perturbations such as geological carbon sequestration and hydrologic fracturing of gas-rich strata, both of which may lead to changes in groundwater flows and chemistries.