Abstract
Hydraulic fracturing is the industry standard for extracting hydrocarbons from shale formations. Attention has been paid to the economic benefits and environmental impacts of this process, yet the biogeochemical changes induced in the deep subsurface are poorly understood. Recent single-gene investigations revealed that halotolerant microbial communities were enriched after hydraulic fracturing. Here, the reconstruction of 31 unique genomes coupled to metabolite data from the Marcellus and Utica shales revealed that many of the persisting organisms play roles in methylamine cycling, ultimately supporting methanogenesis in the deep biosphere. Fermentation of injected chemical additives also sustains long-term microbial persistence, while thiosulfate reduction could produce sulfide, contributing to reservoir souring and infrastructure corrosion. Extensive links between viruses and microbial hosts demonstrate active viral predation, which may contribute to the release of labile cellular constituents into the extracellular environment. Our analyses show that hydraulic fracturing provides the organismal and chemical inputs for colonization and persistence in the deep terrestrial subsurface.
Highlights
IntroductionIt has been estimated that shale gas will provide half of the natural gas in the USA, annually, by 2040, with the Marcellus shale in the Appalachian Basin projected to produce three times more than any other formation[1]
Shale gas accounts for one-third of natural gas energy resources worldwide
From 16S rRNA gene analyses we could not have predicted the role Halanaerobium strains play in fermenting glycine betaine (GB) and hydraulic fracturing (HF) chemical additives such as ethylene glycol, nor would we have associated the Halmonadaceae with detrimental sulfide production
Summary
It has been estimated that shale gas will provide half of the natural gas in the USA, annually, by 2040, with the Marcellus shale in the Appalachian Basin projected to produce three times more than any other formation[1]. Recovery of these hydrocarbons is dependent on hydraulic fracturing technologies, where the high-pressure injection of water and chemical additives generates extensive fractures in the shale matrix. Biomass accumulation within newly generated fractures may reduce their permeability, decreasing natural gas recovery Despite these potential microbial impacts, little is known about the function and activity of microorganisms in hydraulically fractured shale. Frackibacter Halanaerobium Halomonadaceae Marinobacter Methanohalophilus Methanolobus reflected the microbial identities and abundances in the unassembled reads, by comparing genome bin relative abundance to reconstructed near-full-length 16S rRNA genes[11] (Supplementary Data File 1)
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