The Genetics, Biochemistry, and Biophysics of Carbon Cycling by Deep Life

Microbial diversity and function in crystalline basement beneath the Deccan Traps explored in a 3 km borehole at Koyna, western India

“…Most of the inhabitant microorganisms of these oligotrophic, extreme habitats were identified to be well equipped to use the available nutrient resources by deploying a plethora of catabolic machinery, including chemolithotrophic, organotrophic and mixotrophic modes of metabolism (Hallbeck and Pedersen, 2008; Dutta et al ., 2018). Although H 2 ‐driven subsurface lithoautotrophy was considered as the predominant mechanism to fuel deep biosphere ecosystems (Stevens and McKinley, 1995; Lloyd et al ., 2019), the role of organotrophy was also documented (Purkamo et al ., 2015; Wu et al ., 2016; Momper et al ., 2017). Sources of carbon for the heterotrophic metabolism were identified to be abiogenic/biogenic methane, small organic compounds, fermentative products, abiogenic organic acids and ancient organic carbon (Purkamo et al ., 2015; Kieft, 2016).…”

“…In the past, microbial life had been explored in multiple deep (several thousands of meters below surface) subsurface realms ranging from Precambrian basement rocks of Witwatersrand Basin and Fennoscandian Shield to relatively younger continental flood basalts of the Columbia River basin or underneath the Deccan Traps (Hoehler and Jørgensen, 2013; Lau et al ., 2014; Magnabosco et al ., 2016; Dutta et al ., 2018; Magnabosco et al ., 2018; Dutta et al ., 2019; Purkamo et al ., 2020). These investigations revealed that in spite of multiple extremities, including high pressure, temperature, pH, osmolarity along with lack of pore and fracture volumes, and nutrient resources, the deep crystalline igneous crustal systems host enormous microbial diversity (with 2%–19% of Earth's total biomass) and play critical roles in global biogeochemical processes (Lloyd et al ., 2019). There had been convincing lines of evidence that indicated that the deep continental biosphere hosts a huge reservoir of diverse, novel and mostly uncultured and unidentified microorganisms with the potential for answering the most fundamental questions of origin, adaptation and evolution of life on our planet or their significance in global elemental cycles, and in providing valuable resources for humans (Escudero et al ., 2018).…”