185-2 Methanogenesis in Two Geochemically Distinct Analog Environments: Implications for Ocean World Habitability

Session: New Advances and Voices in Geobiology (Posters)

Poster Booth No.: 55

Presenting Author:

Ashley Askins

Authors:

Askins, Ashley M.¹, Zhivkova, Teodora², Som, Sanjoy³, Huber, Julie A.⁴, Templeton, Alexis S.⁵, Hoehler, Tori M.⁶, Elkassas, Sabrina M.⁷, Howells, Alta E. G.⁸

(1) Department of Geological Sciences, University of Colorado Boulder, Boulder, Colorado, USA, (2) Woods Hole Oceanographic Institute, Falmouth, Massachusetts, USA, (3) Blue Marble Space Institute of Science, Seattle, Washington, USA; NASA Ames Research Center, Moffett Field, California, USA, (4) Woods Hole Oceanographic Institute, Falmouth, Massachusetts, USA, (5) Department of Geological Sciences, University of Colorado Boulder, Boulder, Colorado, USA, (6) NASA Ames Research Center, Moffett Field, California, USA, (7) Massachusetts Institute of Technology, Cambridge, Massachusetts, USA; Woods Hole Oceanographic Institute, Falmouth, Massachusetts, USA, (8) Department of Geological Sciences, University of Colorado Boulder, Boulder, Colorado, USA; Blue Marble Space Institute of Science, Seattle, Washington, USA,

Abstract:

Methanogenesis (CO₂ + 4H₂ → CH₄ + 2H₂O) is a seemingly ancient metabolism on Earth and can occur independently of solar energy; as such, methanogenesis has long been considered a model metabolism for life on ice-covered ocean worlds. Modeling and observations suggest that Enceladus, and possibly other ocean worlds, have a distinctly alkaline chemistry, making it important to understand how high alkalinity impacts methanogenesis. Methanogens are known to occur in two distinctly different alkaline environments on Earth, serpentinizing systems and soda lakes. We sought to model the distinctly differing fluid chemistry in these systems to provide a basis for understanding the geochemical context that may drive differences in methanogenesis in these systems. Previous studies suggest that two methanogen species, one from a soda lake in the Altai region of Russia, Methanocalculus natronophilus Z-7105, and another from serpentinized fluid from the Samail Ophiolite in Oman, Methanobacterium strain NSHQ4, have vastly different requirements for CO₂, with M. natronophilus requiring at least one order of magnitude more CO₂  for growth than M. NSHQ4. Further, we observe that M. NSHQ4 requires calcium for growth, whereas M. natronophilus does not, but does require magnesium. Through comparative analysis, we find that Russian soda lakes in the Altai region are magnesium rich relative to calcium. The opposite is true for serpentinized fluids in Oman. Through thermodynamic modeling we found that for the dissolved inorganic carbon (DIC) pool of Russian soda lakes, MgHCO₃⁺ comprises on average 19%, MgCO₃ (aq) comprises 20%, and CO₂ only comprises 2%, making magnesium a strong influence on CO₂ availability. This contrasts serpentinized fluids where CaCO₃(aq) makes up on average 66% and CO₂ makes up 0.02%, making calcium the dominant control of CO₂ availability. Furthermore, CO₂ concentration is 3 to 8 orders of magnitude lower in the serpentinizing system than in Russian soda lakes which, given the potential to impact rates of methanogenesis, would represent a strong ecological driver for the development of lower CO₂ requirements as seemingly expressed in M. NSHQ4. These findings suggest that, despite sharing similarly alkaline pH as a potentially strong constraint on ecology, soda lakes and serpentinizing systems nevertheless express significant differences in carbonate and divalent cation chemistry that are consistent with and may plausibly drive physiological differences in the methanogens that inhabit them.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7166

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