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In the search for life in our Solar System, Mars remains a promising target based on its proximity and similarity to Earth. When Mars transitioned from a warmer, wetter climate to its current dry and freezing conditions, any putative extant life probably retreated into habitable refugia such as the subsurface or the interior of rocks. Terrestrial cryptoendolithic microorganisms ( i.e., those inhabiting rock interiors) thus represent possible modern-day Mars analogs, particularly those from the hyperarid McMurdo Dry Valleys in Antarctica. As DNA is a strong definitive biosignature, given that there is no known abiotic chemistry that can polymerize nucleobases, we investigated DNA detection with MinION sequencing in Antarctic cryptoendoliths after an ∼58-sol exposure in MARTE, a Mars environmental chamber capable of simulating martian temperature, pressure, humidity, ultraviolet (UV) radiation, and atmospheric composition, in conjunction with protein and lipid detection. The MARTE conditions resulted in changes in community composition and DNA, proteins, and cell membrane-derived lipids remained detectable postexposure. Of the multitude of extreme environmental conditions on Mars, UV radiation (specifically UVC) is the most destructive to both cells and DNA. As such, we further investigated if a UVC exposure corresponding to ∼278 martian years would impede DNA detection via MinION sequencing. The MinION was able to successfully detect and sequence DNA after this UVC radiation exposure, suggesting its utility for life detection in future astrobiology missions focused on finding relatively recently exposed biomarkers inside possible martian refugia.

Water tracks in the Antarctic Dry Valleys are dark linear features of increased soil moisture that flow downslope over the spring and summer, providing a source of moisture in a cold-arid desert. They are typically sourced from melting snow, ground ice, and deliquescence (Levy et al. , 2011 ). This research presents the first in-depth study of the activity potential and diversity of microbial communities of Antarctic water tracks. We investigated whether these water track soils are more habitable to microbial communities by ascertaining the differences in diversity, total and culturable cell counts, and microbial respiratory activity in water track soils compared with the adjacent dry soils in Pearse Valley. Total cell counts ranged from 1.47 × 10 3 to 4.17 × 10 5 cells/g dry weight soil. Water track soils had higher total and culturable biomass, in addition to higher microbial activity at 5° and -5°C, compared with adjacent dry soils. Microbial respiration was positively correlated with soil moisture content, but total cell counts and plate counts were not. Surprisingly, microbial community composition did not differ between wet and dry soil communities, and was not related to soil moisture content. The microbial community composition instead appeared to differ spatially based on location and depth. Overall, the data suggest that cold water tracks are more habitable than the surrounding cold-arid soils. Our results suggest that recurring slope lineae, which are dark linear features that grow downslope on Mars over the spring and summer, where liquid water might be a recurring phenomenon, could be sites of astrobiological potential.