Lithoautotrophic Microbial Ecosystems in Deep Basalt Aquifers

Abstract

Bacterial communities were detected in deep crystalline rock aquifers within the Columbia River Basalt Group (CRB). CRB ground waters contained up to 60 μM dissolved H 2 and autotrophic microorganisms outnumbered heterotrophs. Stable carbon isotope measurements implied that autotrophic methanogenesis dominated this ecosystem and was coupled to the depletion of dissolved inorganic carbon. In laboratory experiments, H 2 , a potential energy source for bacteria, was produced by reactions between crushed basalt and anaerobic water. Microcosms containing only crushed basalt and ground water supported microbial growth. These results suggest that the CRB contains a lithoautotrophic microbial ecosystem that is independent of photosynthetic primary production.

Temperatures of aqueous alteration and evidence for methane generation on the parent bodies of the CM chondrites

“…We selected a model temperature of 28˚C because it is a reasonable approximation of the temperatures of carbonate growth for most of our samples (though silicate hydration need not occur at the same temperatures as carbonate precipitation) and it is similar to temperatures of aqueous alteration assumed by previous models of this kind (e.g., Clayton and Mayeda, 1999). While we are aware of no definitive reports of serpentinization occurring at 28˚C in terrestrial rocks, both lab experiments and field observations have been used to suggest that serpentinization (and, important for our further discussion of this model in section 3.2 of this paper, concurrent H 2 generation) occurs at earth-surface temperatures (Neal and Stanger, 1983;Stevens and McKinley, 1995;Stevens and McKinley, 2000). The lowest measured temperature of a serpentinization reaction is 45˚C, in the Lost City hydrothermal field, determined using a hydrogen isotope geothermometer (Proskurowski et al, 2006).…”

A metagenomic window into carbon metabolism at 3 km depth in Precambrian continental crust

“…The surprisingly low to no observed archaeal 16S rRNA genes, the low TOC and DOC concentrations, and the low porosity (0.5% matrix, 0.01% fracture) of the Witwatersrand Basin sites distinguishes them from the more prominent archaeal communities often reported to inhabit the shallower, higher TOC bearing, higher porosity (50-90%) sub-seafloor sediments (Biddle et al, 2006). Instead, the carbon cycling pathways used in the TOC-and DOC-poor Witwatersrand Basin fluids may be more similar to the SLiME communities of the deep Columbia River basalt aquifer (Stevens and McKinley, 1995), the planktonic microbial communities found within the fracture water of the Proterozoic granite in the Fennoscandian Shield (Pedersen, 1997) and autotrophic communities of the Tablelands serpentinite (Brazelton et al, 2012).…”

“…In continental groundwaters and petroleum reservoirs, the microbial abundance and activity are related to proximity to interfaces with organic-rich strata (Chapelle and Lovley, 1990;Krumholz et al, 1997;Bennett et al, 2013). Within continental flood basalts or granitic intrusions, however, autotrophic communities relying upon dissolved inorganic carbon (DIC) may have the dominant role (Stevens and McKinley, 1995;Pedersen, 1997). The low TOC (0.01-0.1 molkg − 1 ) (Silver et al, 2012), dissolved organic carbon (DOC) (~400 μM) and organic acid (~40 μM) concentrations of deep fracture water at the Witwatersrand Basin call into question whether the subsurface microbial communities residing in these fractures are supported by these limited DOC pools or by the larger pools of alternative carbon sources such as biogenic or abiogenic CH 4 (~20 mM), abiogenic C 2-4 hydrocarbons (~500 μM) or DIC (DIC averaging 800 μM) (Kieft et al, 2005;Onstott et al, 2006;Sherwood Lollar et al, 2006).…”

[FeFe]-hydrogenase in Yellowstone National Park: evidence for dispersal limitation and phylogenetic niche conservatism

“…High concentrations of H 2 have been reported in a variety of environments that include the deep subsurface (Stevens and McKinley, 1995), hydrothermal vents (Jannasch and Mottl, 1985), salt-evaporation ponds (Hoehler et al, 2001) and a range of terrestrial geothermal features (Conrad et al, 1985;Inskeep and McDermott, 2005;Spear et al, 2005). H 2 is an important source of energy for the maintenance and growth of microbial populations (Wolin, 1982;Morita, 2000) and has recently been postulated to be the primary fuel supporting a number of microbial assemblages (Stevens and McKinley, 1995;Chapelle et al, 2002), including those inhabiting geothermal spring environments (Conrad et al, 1985;Spear et al, 2005).…”