Hydrogenotrophic Methanogenesis at 7-12 mbar by Methanosarcina barkeri under Simulated Martian Atmospheric Conditions

Abstract

AbstractIt is widely accepted that ancient Mars hosted long-lived habitable environments, and that habitable refugia may persist in the subsurface today. The presence and behavior of methane gas in the Martian atmosphere makes a compelling case to study methanogenesis as a potential biosignature under simulated Mars surface or shallow subsurface conditions. Methanogenic archaea have demonstrated tolerance to prolonged exposure to desiccation, high salinity, strong oxidants, UVC irradiation, and extremes in temperature, pH, and pressure. We investigated hydrogenotrophic methanogenesis and accompanying gene expression patterns inMethanosarcina barkeriin response to sustained hypobaria (7–12 mbar), low temperature (0˚C), and a CO2-dominated gas mixture simulating Martian atmospheric conditions. We observed statistically significant CH4production under all assayed conditions, including at 7–12 mbar. Comparative transcriptomics in reference to control conditions (i.e., 30˚C, 1500 mbar, 80:20 H2:CO2) revealed that the partial pressure of atmospheric H2was the most important factor in regulating methanogenesis. We conclude an extant methanogenic biosphere could be supported throughout the Martian lithosphere in habitable subsurface refugia and microhabitats.