Low Pressure Tolerance by Methanogens in an Aqueous Environment: Implications for Subsurface Life on Mars
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The low pressure at the surface of Mars (average: 6 mbar) is one potentially biocidal factor that any extant life on the planet would need to endure. Near subsurface life, while shielded from ultraviolet radiation, would also be exposed to this low pressure environment, as the atmospheric gas-phase pressure increases very gradually with depth. Few studies have focused on low pressure as inhibitory to the growth or survival of organisms. However, recent work has uncovered a potential constraint to bacterial growth below 25 mbar. The study reported here tested the survivability of four methanogen species (Methanothermobacter wolfeii, Methanosarcina barkeri, Methanobacterium formicicum, Methanococcus maripaludis) under low pressure conditions approaching average martian surface pressure (6 mbar – 143 mbar) in an aqueous environment. Each of the four species survived exposure of varying length (3 days – 21 days) at pressures down to 6 mbar. This research is an important stepping-stone to determining if methanogens can actively metabolize/grow under these low pressures. Additionally, the recently discovered recurring slope lineae suggest that liquid water columns may connect the surface to deeper levels in the subsurface. If that is the case, any organism being transported in the water column would encounter the changing pressures during the transport.
KeywordsMethanogens Mars Methane Low pressure Survival
The authors thank Dr. Chris McKay for his helpful suggestions during the review process. The authors would like to acknowledge Walter Graupner at the Arkansas Center for Space and Planetary Sciences for his research assistance. The authors would also like to thank Larry Joe Steeley Jr. (Rainbow Technology, Pelham, AL) for his donation of duct seal putty. This research was supported by a grant from the National Aeronautics and Space Administration (NASA) Astrobiology: Exobiology and Evolutionary Biology Program, grant #NNX12AD90G and by grants from the Arkansas Space Grant Consortium.
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