Subsurface Microbial Habitats in an Extreme Desert Mars-Analog Environment

Abstract

Sediments in the hyper-arid core of the Atacama Desert are a terrestrial analog to Mars regolith. Understanding the distribution and drivers of microbial life in the sediment may give critical clues on how to search for biosignatures on Mars. Here, we identify the spatial distribution of highly specialized bacterial communities in previously unexplored depth horizons of subsurface sediments to a depth of 800 mm. We deployed an autonomous rover in a mission-relevant Martian drilling scenario with manual sample validation. Subsurface communities were delineated by depth related to sediment moisture. Geochemical analysis indicated soluble salts and minerology that influenced water bio-availability, particularly in deeper sediments. Colonization was also patchy and uncolonized sediment was associated with indicators of extreme osmotic challenge. The study identifies linkage between biocomplexity, moisture and geochemistry in Mars-like sediments at the limit of habitability and demonstrates feasibility of the rover-mounted drill for future Mars sample recovery.

Inhabited subsurface wet smectites in the hyperarid core of the Atacama Desert as an analog for the search for life on Mars

“…The known patchy distribution of subsurface habitats in the hyperarid core of the Atacama 29,120,121 suggests that the search for biosignatures on Mars with the scientific payloads of future rovers will be a difficult task, as potential biosignatures could be similarly unevenly distributed throughout the Martian subsurface. Because the subsurface microbial community discovered in Yungay has adapted to an environment of persistent superficial drought with rare exposure to water, this expands potentially habitable environments on Mars to those with evidence for sporadic exposure to water, rather than persistent exposure.…”

Energetic Basis of Microbial Growth and Persistence in Desert Ecosystems

“…The combined effects of other environmental factors may reduce the capacity to generate sufficient energy during one short "water pulse." For instance, salt accumulated in hyper-arid soils reduces water bioavailability (92)(93)(94), the low mean temperatures in Antarctic soils reduce cellular metabolism (95), and the highly limited organic carbon and bioavailable nitrogen in hyper-arid soils may restrict heterotrophic processes (5). Overall, the ability of xerotolerant microorganisms inhabiting desert soils to accumulate and utilize long-term energy storage compounds requires more extensive study, especially in situ.…”

“…However, it is known that some methylotrophs are in high relative abundance in some desert soils; an example is Methylobacterium radiotolerans, which dominates the microbial communities at depths below 5 meters in the Playa of the Atacama Desert soils (94).…”

The Hypopiezotolerant Bacterium, Serratia liquefaciens, Failed to Grow in Mars Analog Soils under Simulated Martian Conditions at 7 hPa

“…Life 2020, 10, 77 2 of 17 saline and acidic geochemistries like in Rio Tinto, Spain [1][2][3][4][5][6][7]. In contrast, others have proposed that microorganisms recovered from Mars spacecraft should be used as model organisms [8][9][10][11] because they might plausibly be dispersed onto the Martian terrain during lander or rover missions, and thus, might act as inoculum for contaminating sites of scientific interest.…”