Survival and metabolism of \(\textit{Methanosarcina soligelidi}\) under simulated Martian subsurface conditions

Abstract

Variable methane concentrations imply that there are active methane production and destruction processes in the Martian atmosphere. In addition, recent rover and orbiter observations have determined that water may be present in perchlorate brine appearing in the shallow subsurface of Mars during diurnal temperature cycles. The composition of the Martian atmosphere and regolith may be sufficient to allow methanogenesis through the hydrogenotrophic pathway, and the presence of meteoric acetate on the surface could allow for aceticlastic methanogenesis. This project investigates if a terrestrial methanogen could survive and metabolize under the physical and mineralogical conditions present in an analog environment to the shallow subsurface of Mars. Permafrost methanogen \(\textit{Methanosarcina soligelidi}\) has been previously shown to survive under Martian surface temperatures. A secondary goal is to determine which metabolic pathway and substrate this methanogen prefers under low pressure. To test these questions, \(\textit{M. soligelidi}\) was incubated anaerobically at optimal growth temperature in nutrient-replete media containing added acetate under varied low pressures of \(\mathrm{H_2}\)-\(\mathrm{CO_2}\) headspace in gas-tight canisters ranging from 10 to 500 mbar, and under \(\mathrm{H_2}\)-\(\mathrm{CO_2}\) at ambient pressure in stoppered serum vials for comparison. Half of incubated cultures received Mars regolith analog JSC-1. Headspace gas of all vessels was sampled at regular intervals and analyzed for methane production and \(\mathrm{H_2}\) consumption. Cultures at all conditions, down to 10 mbar, survived and produced methane for the duration of the experiment. Methanogens utilized both the hydrogenotrophic and aceticlastic pathway to produce methane but seemed to rely more on the latter. This work may be continued using the established methods with additional variables such as decreased temperature and perchlorate salinity to further investigate \(\textit{M. soligelidi}\) success and metabolism under comprehensive Martian subsurface conditions. Functional genes associated with survival under Martian conditions may be identified via transcriptomics.