Trends and future challenges in sampling the deep terrestrial biosphere

Abstract

Research in the deep terrestrial biosphere is driven by interest in novel biodiversity and metabolisms, biogeochemical cycling, and the impact of human activities on this ecosystem. As this interest continues to grow, it is important to ensure that when subsurface investigations are proposed, materials recovered from the subsurface are sampled and preserved in an appropriate manner to limit contamination and ensure preservation of accurate microbial, geochemical, and mineralogical signatures. On February 20th, 2014, a workshop on “Trends and Future Challenges in Sampling The Deep Subsurface” was coordinated in Columbus, Ohio by The Ohio State University and West Virginia University faculty, and sponsored by The Ohio State University and the Sloan Foundation’s Deep Carbon Observatory. The workshop aims were to identify and develop best practices for the collection, preservation, and analysis of terrestrial deep rock samples. This document summarizes the information shared during this workshop.

Life in High-Temperature Environments

“…Estimates of the habitable volume of the subsurface and biomass inhabiting the subsurface are still rough, due primarily to uncertainty in the extent of liquid water in the subsurface; however, some estimates have been made that more than half of Earth's biomass resides in the subsurface (21,22). Most sampled subsurface environments have yielded microbial cells or signatures of microbial life, although the low biomass of these habitats and the engineering challenges associated with subsurface exploration mandate strict contamination controls (23), which have been variably applied. Recently, deep fracture fluids isolated since the Precambrian have been sampled and lacked detectable biomarkers or cultivable microorganisms (24).…”

Potential for hydrogen-oxidizing chemolithoautotrophic and diazotrophic populations to initiate biofilm formation in oligotrophic, deep terrestrial subsurface waters

“…The deep biome is the largest microbial ecosystem on earth [9], and the deep continental biosphere is estimated to host 2 to 19% of earth’s total biomass [10]. Although a large proportion of the earth’s microbial cells reside in the deep biosphere, our knowledge of the biology and identity of these organisms is scarce [11]. One reason for this is the difficulty to obtain uncontaminated samples.…”

“…The present study was carried out at the Äspö Hard Rock Laboratory (Äspö HRL). This 460-m-deep underground laboratory circumvents many problems associated with contamination of the low biomass samples of the deep biosphere [11]. These advantages include that the groundwaters are physically separated from the oxidizing environment in the tunnel and that the flow of water into the boreholes is by gravity rather than pumping.…”

Earth as a Microbial Habitat

“…Although such fluids are essential for the drilling process, many of these substrates provide an excellent environment for supporting microbial growth (Beeman and Suflita, 1989) and therefore, can lead to contamination of recovered materials. A wide range of techniques are applied for monitoring contamination during drilling, including the use of chemical, microbiological, and particle tracers that may either be added to drilling fluids or applied to drilling apparatus (Kieft, 2010;Wilkins et al, 2014a). Tracers that have been used in subsurface geomicrobiological investigations are provided in Table 5.1.…”