Abstract
SummaryMicrobial 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.
Highlights
The majority of prokaryotes on Earth live in the subsurface and are present to depths in excess of 3 km (Parkes et al, 2014)
Subsurface microorganisms maybe be more reliant on the geosphere for energy supply (Pedersen, 2000), including H2 which has a range of geosphere sources
Low temperature (~20 C) basalt weathering/oxidation had been suggested to fuel a H2-based microbial ecosystem in the Columbia River Basalt Aquifer (Stevens and McKinley, 1995). This community subsequently was considered to be heterotrophic instead, as little H2 formation occurred under simulated in situ conditions and because ferrous iron concentrations would have been limiting (Anderson et al, 1998)
Summary
The majority of prokaryotes on Earth live in the subsurface and are present to depths in excess of 3 km (Parkes et al, 2014). To enhance mineral-H2 formation at 67 C, silica milling was conducted in an oil bath (Supporting Information Fig. S1B) to provide extended periods of heated milling and this was combined with headspace flushing (Fig. 2). Effective, resulting in significant H2 formation after headspace flushing, which did not occur in the Anderson et al experiments.
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