Life Underground

The central research theme of our NAI proposal is the search for life in the subsurface. While the target sites are drill holes into continental and marine strata on Earth, they are of clear astrobiological significance. The sites and corresponding rock, sediment, and water samples serve as field testing sites of new technologies and experimental methods, and as analog environments for the exploration of the Martian subsurface. The key objectives of our proposed study are: 1) field applications of new technologies that are designed for in situ detection of cells and organic matter on rock and sediments; 2) guided cultivation of subsurface microorganisms (the ‘intraterrestrials’) using a combination of traditional and non-traditional approaches informed by genomics and geochemistry; 3) characterization of microbial function in low energy environments; and 4) microbial reaction energetics and extracellular electron transport. To accomplish these objectives, we will 1) develop, modify, and field-test new tools and technologies (focused predominantly on deep UV microscopy and deep UV Raman spectroscopy) to detect cells and organic matter in situ and on rock samples; 2) cultivate subsurface microbiota using geochemically and biochemically designed growth media, ‘on chip’ cultivation with electrodes to control redox potentials, and single-cell capture approaches; 3) apply passive and metabolic tracers to environmental samples with low cell numbers and analyze by nanoSIMS in combination with other non-destructive methods; and 4) generate a thermodynamic/kinetic framework of redox reaction energetics in a variety of subsurface environments, complemented with laboratory experiments aimed at examining the energy partitioning between growth and maintenance. Our research responds directly to several goals called out in the NASA NAI roadmap—-specifically, how to “recognize signatures of life” and “identify biosignatures that can reveal and characterize past or present life in ancient samples from Earth” (Goal 7), and “understand how life on Earth and its planetary environment have co-evolved” and “investigate the evolving relationships between Earth and its biota by integrating evidence from the geosciences and biosciences that shows how life evolved, responded to environmental change, and modified environmental conditions” (Goal 4). Life detection and characterization are fundamental to NASA’s astrobiology mission, and if life exists or ever existed on Mars, the evidence will be most likely found in the subsurface.