EXPLORING THE ANAEROBIC OXIDATION OF METHANE IN SHALLOW GROUNDWATER AS A MARTIAN MICROBIAL ANALOG

It has been long theorized that microbial life could exist in the ancient or modern Martian subsurface. On Mars, there is ample evidence of methane production from ancient serpentinization and low modern levels of methane as well as sulfate-rich and iron-rich minerals detected at the near-surface. This indicates the potential for methane-sulfate and methane-iron redox systems in the shallow Martian subsurface. On Earth, it’s known a consortium of bacteria and archaea can work together to oxidize methane and reduce sulfate via the Anaerobic Oxidation of Methane (AOM). Additionally, there is evidence Earth microbes achieve AOM through the reduction of iron (III). While these geochemical parallels highlight AOM as a potential Martian microbial metabolism, we know very little about AOM in near-surface groundwaters on Earth. The exact composition of Martian subsurface waters in the present and past are unknown; however, some theorized compositions are similar to that of shallow groundwater in the Appalachian Basin of Pennsylvania (USA). We collected groundwater samples emitting H₂S and methane from inside Pennsylvania abandoned oil and gas wells. The samples were used as inoculant for enrichment cultures. After the cultures are injected with ¹³C labeled methane, they will be analyzed for the depletion of sulfate and the production of iron (II) and ¹³CO₂. AOM occurring in shallow Pennsylvania groundwater would further support AOM as a plausible microbial mechanism on Mars.