Chemolithotrophy in the continental deep subsurface: Sanford Underground Research Facility (SURF), USA

Abstract

The deep subsurface is an enormous repository of microbial life. However, the metabolic capabilities of these microorganisms and the degree to which they are dependent on surface processes are largely unknown. Due to the logistical difficulty of sampling and inherent heterogeneity, the microbial populations of the terrestrial subsurface are poorly characterized. In an effort to better understand the biogeochemistry of deep terrestrial habitats, we evaluate the energetic yield of chemolithotrophic metabolisms and microbial diversity in the Sanford Underground Research Facility (SURF) in the former Homestake Gold Mine, SD, USA. Geochemical data, energetic modeling, and DNA sequencing were combined with principle component analysis to describe this deep (down to 8100 ft below surface), terrestrial environment. SURF provides access into an iron-rich Paleoproterozoic metasedimentary deposit that contains deeply circulating groundwater. Geochemical analyses of subsurface fluids reveal enormous geochemical diversity ranging widely in salinity, oxidation state (ORP 330 to −328 mV), and concentrations of redox sensitive species (e.g., Fe2+ from near 0 to 6.2 mg/L and Σ S2- from 7 to 2778μg/L). As a direct result of this compositional buffet, Gibbs energy calculations reveal an abundance of energy for microorganisms from the oxidation of sulfur, iron, nitrogen, methane, and manganese. Pyrotag DNA sequencing reveals diverse communities of chemolithoautotrophs, thermophiles, aerobic and anaerobic heterotrophs, and numerous uncultivated clades. Extrapolated across the mine footprint, these data suggest a complex spatial mosaic of subsurface primary productivity that is in good agreement with predicted energy yields. Notably, we report Gibbs energy normalized both per mole of reaction and per kg fluid (energy density) and find the later to be more consistent with observed physiologies and environmental conditions. Further application of this approach will significantly expand our understanding of the deep terrestrial biosphere.

Genomic Description of ‘Candidatus Abyssubacteria,’ a Novel Subsurface Lineage Within the Candidate Phylum Hydrogenedentes

“…Geochemical measurements were made either on site, or upon return to the laboratory (Osburn et al, 2014). In this study, we examined deep fracture fluids from legacy boreholes drilled ∼1.5 kilometers below surface (kmbs), accessing a deeply circulating terrestrial aquifer.…”

An oligotrophic deep-subsurface community dependent on syntrophy is dominated by sulfur-driven autotrophic denitrifiers

“…The metabolic capability of the predominant sulfur-driven autotrophic denitrifiers drives the links between the N, S, and C cycles. Previous studies have reported the high energetic potential of S-N reactions in other deep continental sites (50), and expression of mRNA coding for nitrate reductase in marine subseafloor sediment cores where NO 3 − was not detectable (51), indicating that the role of nitrate reduction and/or denitrification in the deep subsurface has been overlooked. Active subsurface metabolic landscapes that intertwine H 2 -driven processes, S-N coupling, and dissimilatory NO 3 -dependent reactions may be more prevalent in both continental and marine subsurface systems than previously thought.…”

The Sanford Underground Research Facility at Homestake

“…Biodiversity (BHSU) Microbiology Surface, 300L, [45,46,47] 2000L, 4100L, 4550L, 4850L Biofuels (SDSMT) Biofuels 4550L, 4850L, [48,49,50,51], 5000L [52,53,54,55] Lignocellulose (SDSU) Biofuels 1700L, 4850L [56,57] Syngas (SDSMT) Biofuels 4850L [58,59,60] Life UndergroundWater in drill holes, Surface, 800L, [61] NASA Astrobiology Institute geomicrobiology 4850L Engineering Xilinx, Inc. Chip error testing 4850L The LUX collaboration published results in October 2013 from their first underground data run [23] and started a longer run (nominally 300 live days) in October 2014. LUX is expecting to complete their experimental program in 2016.…”