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Rock‐crushing derived hydrogen directly supports a methanogenic community: significance for the deep biosphere

Parkes, Ronald John, Berlendis, Sabrina, Roussel, Erwan G., Bahruji, Hasiliza, Webster, Gordon, Oldroyd, Anthony, Weightman, Andrew J., Bowker, Michael, Davies, Philip R., Sass, Henrik
Environmental microbiology reports 2019 v.11 no.2 pp. 165-172
aerobes, biosphere, earthquakes, granite, hydrogen, hydrogen production, mechanochemistry, methane, methane production, methanogens, microbial communities, oxidants, photosynthesis, potential energy
Microbial populations exist to great depths on Earth, but with apparently insufficient energy supply. Earthquake rock fracturing produces H₂ from mechanochemical water splitting, however, microbial utilization of this widespread potential energy source has not been directly demonstrated. Here, we show experimentally that mechanochemically generated H₂ from granite can be directly, long‐term, utilized by a CH₄ producing microbial community. This is consistent with CH₄ formation in subsurface rock fracturing in the environment. Our results not only support water splitting H₂ generation as a potential deep biosphere energy source, but as an oxidant must also be produced, they suggest that there is also a respiratory oxidant supply in the subsurface which is independent of photosynthesis. This may explain the widespread distribution of facultative aerobes in subsurface environments. A range of common rocks were shown to produce mechanochemical H₂, and hence, this process should be widespread in the subsurface, with the potential for considerable mineral fuelled CH₄ production.