The deep, hot biosphere: Twenty-five years of retrospection

Abstract

Twenty-five years ago this month, Thomas Gold published a seminal manuscript suggesting the presence of a "deep, hot biosphere" in the Earth's crust. Since this publication, a considerable amount of attention has been given to the study of deep biospheres, their role in geochemical cycles, and their potential to inform on the origin of life and its potential outside of Earth. Overwhelming evidence now supports the presence of a deep biosphere ubiquitously distributed on Earth in both terrestrial and marine settings. Furthermore, it has become apparent that much of this life is dependent on lithogenically sourced high-energy compounds to sustain productivity. A vast diversity of uncultivated microorganisms has been detected in subsurface environments, and we show that H, CH, and CO feature prominently in many of their predicted metabolisms. Despite 25 years of intense study, key questions remain on life in the deep subsurface, including whether it is endemic and the extent of its involvement in the anaerobic formation and degradation of hydrocarbons. Emergent data from cultivation and next-generation sequencing approaches continue to provide promising new hints to answer these questions. As Gold suggested, and as has become increasingly evident, to better understand the subsurface is critical to further understanding the Earth, life, the evolution of life, and the potential for life elsewhere. To this end, we suggest the need to develop a robust network of interdisciplinary scientists and accessible field sites for long-term monitoring of the Earth's subsurface in the form of a deep subsurface microbiome initiative.

Geological gas‐storage shapes deep life

“…Given the volume of town gas stored and that the latter was composed of at least 50% H 2 , it is expected that ≈40 × 10 3 Nm 3 of H 2 could have been dissolved. The sulfate concentration decreased in water sampled in the closest monitoring wells, undoubtedly due to the SRM activity, for which the redox pair H 2 /SO 4 is thermodynamically favourable in these types of environments (Colman et al ., ), as observed in the Siberian oil fields (Bonch‐Osmolovskaya et al ., ). We suggest that, following the disappearance of the sulfates, the methanogenic archaea became more competitive (Pb_C_1 and Pb_C_4) and even dominated the SRM metabolic group (Pb_C_2) for a sulfate concentration weaker than 2.9 mg/l (Fig.…”

Constrained proteome allocation affects coexistence in models of competitive microbial communities

“…For example, "metabolic strategies" in our framework correspond to the proteome fractions ϕ σi . Additionally, our model also includes the proteome finiteness constraint given by Eq (2). The final expression of this constraint in our equations is significantly different from similar constraints that have been studied in the consumer-resource framework 31 22 to the case of N R resources: we assume that the sector allocated by species σ for nutrient uptake and metabolization is subdivided into smaller fractions ϕ σi = ϕ P σi , each one dedicated to a specific resource.…”

Iron‐ and aluminium‐induced depletion of molybdenum in acidic environments impedes the nitrogen cycle

“…In addition to limiting nitrate reduction by a single organism as shown in this study, a lack of Mo may shift the microbial community structure such that other growth modes are more energetically favourable and become dominant, similar to what was found in estuarine environments (Howarth and Cole, ). It might be expected to take longer to re‐establish nitrate to non‐contaminant concentrations in these Mo‐depleted environments (Colman et al ., ).…”