Methane Production on Mars-Relevant Clay Minerals and Simulant Regolith

Over the course of Martian history, the presence of atmospheric carbon dioxide and potential subsurface molecular hydrogen (H₂), in addition to potential surface and subsurface liquid water, suggests that the Martian subsurface, at minimum, may once have been habitable, particularly to autotrophic chemosynthetic microorganisms. In addition, the widespread nature of clays and other minerals on Mars could have provided sufficient nutrients to support microbial life. Here we tested four methanogenic species (Methanosarcina barkeri, Methanobacterium formicicum, Methanothermobacter wolfeii, and Methanococcus maripaludis) in the presence of illite, nontronite, and Mojave Mars Simulant (MMS), in their standard growth medium. We aimed to determine whether the presence of certain Mars simulants inhibited, promoted, or had no effect on methane (CH₄) production by these microorganisms. The same methanogens were also tested in the presence of montmorillonite, H₂, sodium sulfide (Na₂S), and bicarbonate buffer to determine if this clay could support biotic CH₄ production. Three of the four methanogens tested (M. barkeri, M. formicicum, and M. wolfeii) were capable of CH₄ production in the presence of both clay minerals and MMS, as well as in cultures containing only 10% (w/v) montmorillonite, H₂, Na₂S, and bicarbonate buffer. Conversely, M. maripaludis, a halophile, showed the greatest sensitivity of the four methanogens tested; however, the presence of 5% (w/v) montmorillonite enabled greater CH₄ production under certain circumstances compared to cultures containing the organism's standard growth medium alone. Overall, these results suggest that the presence of clay minerals on Mars does not preclude the survivability and growth of methanogens in a potential subsurface habitat. In fact, these geological components may provide sufficient nutrients to support microbial growth and survivability.