title: Hydraulic fracturing offers view of microbial life in the deep terrestrial subsurface.
abstract: Horizontal drilling and hydraulic fracturing are increasingly used for recovering energy resources in black shales across the globe. Although newly drilled wells are providing access to rocks and fluids from kilometer depths to study the deep biosphere, we have much to learn about microbial ecology of shales before and after 'fracking'. Recent studies provide a framework for considering how engineering activities alter this rock-hosted ecosystem. We first provide data on the geochemical environment and microbial habitability in pristine shales. Next, we summarize data showing the same pattern across fractured shales: diverse assemblages of microbes are introduced into the subsurface, eventually converging to a low diversity, halotolerant, bacterial and archaeal community. Data we synthesized show that the shale microbial community predictably shifts in response to temporal changes in geochemistry, favoring conservation of key microorganisms regardless of inputs, shale location or operators. We identified factors that constrain diversity in the shale and inhibit biodegradation at the surface, including salinity, biocides, substrates and redox. Continued research in this engineered ecosystem is required to assess additive biodegradability, quantify infrastructure biocorrosion, treat wastewaters that return to the surface and potentially enhance energy production through in situ methanogenesis.
authors: Department of Civil, Environmental and Geodetic Engineering, The Ohio State University, 2070 Neil Avenue, 470 Hitchcock Hall, Columbus, OH 43210, USA mouser.19@osu.edu.
authors: Paula J
authors: PJ
authors: Mouser
authors: Department of Microbiology, The Ohio State University, 484 West 12th Avenue, Columbus, OH 43210, USA.
authors: Mikayla
authors: M
authors: Borton
authors: Divisions of Solid Earth Dynamics and Water, Climate and the Environment, School of Earth Sciences, The Ohio State University, 125 South Oval Mall, 275 Mendenhall Lab, Columbus, OH 43210, USA.
authors: Thomas H
authors: TH
authors: Darrah
authors: Department of Biology, University of Akron-Wayne College, 1901 Smucker Road, Orrville, OH 44667, USA.
authors: Angela
authors: A
authors: Hartsock
authors: Department of Microbiology, The Ohio State University, 484 West 12th Avenue, Columbus, OH 43210, USA.
authors: Kelly C
authors: KC
authors: Wrighton
mesh_terms: D001105:Archaea / Q000145:classification* / Q000302:isolation & purification; D001419:Bacteria / Q000145:classification* / Q000302:isolation & purification; D017753:Ecosystem; D004777:Environment; D000067071:Hydraulic Fracking; D059206:Natural Gas; D061329:Oil and Gas Fields / Q000382:microbiology*; D012988:Soil Microbiology; D062065:Wastewater / Q000382:microbiology*
chemical_list: D059206:Natural Gas; D062065:Wastewater
keywords: Marcellus; fracking; halotolerant bacteria; methanogens; natural gas; shale