The stable carbon isotope fractionation of methanogenesis products at complete carbon consumption

Journal Article · Wed Oct 29 00:00:00 EDT 2025 · Geochemical Perspectives Letters

DOI:https://doi.org/10.7185/geochemlet.2543· OSTI ID:3013982

Batther, Harpreet K. ^[1]; Templeton, A. S. ^[1]; Hoehler, T. ^[2]; Howells, A. ^[2]; Bill, M. ^[3]; Gropp, J. ^[4]; Kopf, S. ^[1]

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1. University of Colorado, Boulder, CO (United States)
2. Ames Research Center, Moffett Field, CA (United States)
3. Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
4. University of California, Berkeley, CA (United States)

The stable carbon isotope signature (δ¹³C) of methane (CH₄) is used to discriminate between biological, thermogenic, and abiotic sources. Methanogens, or methane producing archaea, inhabit a broad range of chemical conditions. Many of these environments are replete in dissolved inorganic carbon (DIC), causing isotopically depleted δ¹³C biogenic CH₄. However, some extreme environments inhabited by methanogens, such as serpentinising systems, exhibit low carbon dioxide (CO₂) availability, replete H₂, and isotopically enriched δ¹³C CH₄ that is outside the known biogenic range. We measured the δ¹³C of CO₂, biomass, lipids, and CH₄ during hydrogenotrophic methanogenesis under hydrogen replete conditions with a limited carbon pool to investigate carbon isotope dynamics at complete DIC consumption. As theory predicts, we found that the final, accumulated methane δ¹³C values closely reflect the δ¹³C of the initial DIC supply, and that methane is more ¹³C enriched than biomass and lipids. This provides the first experimental evidence that methanogens can achieve complete carbon consumption and thus can produce accumulated CH₄ products that isotopically reflect the initial CO₂. These data show that the range of possible δ¹³C values from biogenic methane needs to be expanded for natural environments impacted by extreme carbon limitation.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: National Aeronautics and Space Administration (NASA); USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division (MSE); USDOE Office of Science (SC), Biological and Environmental Research (BER). Earth & Environmental Systems Science (EESS)
• Grant/Contract Number: AC02-05CH11231
• Other Award/Contract Number: 21-EXO21-0055
• OSTI ID: 3013982
• Alternate ID(s): OSTI ID: 3013983
• Journal Information: Geochemical Perspectives Letters, Journal Name: Geochemical Perspectives Letters Vol. 37; ISSN 2410-3403; ISSN 2410-339X
• Publisher: European Association of Geochemistry
• Country of Publication: United States
• Language: English

Related Subjects

biomass
carbon
carbon dioxide
carbon limitation
hydrogenotrophic
isotope fractionation
isotopes
lipids
methane
methanogenesis