The detection of silica-rich dust particles, as an indication for ongoing hydrothermal activity, and the presence of water and organic molecules in the plume of Enceladus, have made Saturn’s icy moon a hot spot in the search for potential extraterrestrial life. Methanogenic archaea are among the organisms that could potentially thrive under the predicted conditions on Enceladus, considering that both molecular hydrogen (H2) and methane (CH4) have been detected in the plume. Here we show that a methanogenic archaeon, Methanothermococcus okinawensis, can produce CH4 under physicochemical conditions extrapolated for Enceladus. Up to 72% carbon dioxide to CH4 conversion is reached at 50 bar in the presence of potential inhibitors. Furthermore, kinetic and thermodynamic computations of low-temperature serpentinization indicate that there may be sufficient H2 gas production to serve as a substrate for CH4 production on Enceladus. We conclude that some of the CH4 detected in the plume of Enceladus might, in principle, be produced by methanogens.

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Climate neutral and sustainable energy sources will play a key role in future energy production. Biomethanation by gas to gas conversion of flue gases is one option with regard to renewable energy production. Here, we performed the conversion of synthetic carbon monoxide (CO)-containing flue gases to methane (CH4) by artificial hyperthermophilic archaeal co-cultures, consisting of Thermococcus onnurineus and Methanocaldococcus jannaschii, Methanocaldococcus vulcanius, or Methanocaldococcus villosus. Experiments using both chemically defined and complex media were performed in closed batch setups. Up to 10 mol% CH4 was produced by converting pure CO or synthetic CO-containing industrial waste gases at a high rate using a co-culture of T. onnurineus and M. villosus. These findings are a proof of principle and advance the fields of Archaea Biotechnology, artificial microbial ecosystem design and engineering, industrial waste-gas recycling, and biomethanation.

In this study (Taubner et al.2018), three different methanogenic archaea (Methanothermococcus okinawensis, Methanothermobacter marburgensis, and Methanococcus villosus) were tested for metabolic activities and growth under putative Enceladus-like conditions, including high pressure experiments and tests on the tolerance towards potential gaseous and liquid inhibitors detected in Enceladus’ plume. In particular, M. okinawensis, an isolate from a deep marine trench (Takai et al.2002), showed tolerance towards all of the added inhibitors and maintained methanogenesis even in the range of 10 to 50 bar. Further, we were able to show that H2 production based on serpentinization may be sufficient to fuel such methanogenic life on Enceladus. The experiments revealed that methanogenesis could, in principle, be feasible under Enceladus-like conditions.