Editorial: The rocky biosphere: New insights from microbiomes at rock-water interfaces and their interactions with minerals

Abstract

The deep subsurface hosts one of the largest, yet least explored ecosystems on Earth. Exploration of the deep biosphere has implications for our understanding of the sustainability of our planet, particularly in ecosystems where life faces the extreme deprivation of energy and nutrients (Hoehler and Jørgensen, [3]). Our knowledge of lifeforms and processes in this ecosystem also have far-reaching astrobiological implications that influence exploration strategy of planetary bodies such as Mars and icy moons (Onstott et al., [7]). Microbial communities in the subsurface account for a significant proportion of global biomass on Earth (McMahon and Parnell, [6]; Bar-On et al., [1]; Magnabosco et al., [5]; Wang et al., [8]). These subterranean communities may also help us to understand the evolutionary history of microbial life on our planet. A recent study demonstrated the slow evolution of subsurface microbes (Becraft et al., [2]), thus primitive characters might be retained. Additionally, biosignatures of deep ancient life might be omnipresent as fossilized biofilms and isotope fingerprints in deep fracture coatings (Ivarsson et al., [4]). Research studies on live communities in the deep rock-hosted biosphere are restricted by the hard-to-reach nature of this ecosystem. Access to the deep biosphere requires deep sea drilling, deep continental drilling, or relying on existing subsurface infrastructure (tunnels, mines, research facilities). These limitations call for general conceptual studies, as well as detailed site-specific studies for various settings and physico-chemical conditions. In this Research Topic, studies from deep continental settings and oceanic settings are presented and describe both fluid-bound communities and biofilm communities, as well as a review that summarizes the state of the field. Chemoautotrophic archaea are globally distributed in deep-sea hydrothermal vent and sub-vent ecosystems. At the Mid-Cayman Rise, hydrogenotrophic methanogens from the genus Methanothermococcus comprised the most abundant lineage of archaea observed in venting fluids, yet how they adapt and diversify in these habitats remain largely unknown.