10-4 Reevaluating the Role of Methanogens in Sedimentary Biogeochemistry.

Session: Geochemistry and Mineralogy (Posters)

Presenting Author:

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Abstract:

Methanogenic archaea (MA) (i.e., methanogens) are ancient microorganisms that have played a fundamental role in establishing and regulating Earth’s climate. They were involved in the formation of some of Earth’s earliest ecosystems, microbial mats, and their lithified counterpart, stromatolites, yet their role in these ancient and modern-day communities remains largely unresolved. Here, we investigated two geomicrobial aspects of MA in Fayetteville Green Lakes, a Proterozoic Ocean analogue.

Interactions between sulfidogens and MA were studied by in situ measurements of net CH₄ fluxes, biogeochemical (slurry) experiments, and combined with MA enrichments and molecular diversity. Methanolobus spp., methylotrophic MA, were identified using 16S archaeal-specific primers. Slurry experiments of Green Lakes surface mats show significantly reduced methane production in treatments inhibiting sulfidogens and high methane production in untreated slurries. This result suggests a potentially synergistic relationship between sulfide producers and MA rather than a competitive one. In this scenario, methanogens may be consuming methylated sulfur compounds, non-competitive substrates for MA, which can be produced in the presence of sulfide conditions in the organic-rich microbial mats. Although sulfide production was always observed, Deltaproteobacteria (classical sulfate reducers) were not present. However, sulfidogenic bacteria were identified in abundance from 16S data.

Lithification of microbial mats results from microbial metabolism and properties of exopolymeric substances. EPS in microbial mats is typically acidic, having a strong binding capacity for cations. In contrast, MA EPS have an unusual composition, tightly bound to the cell surfaces, comprising an alkaline sugar matrix and minimal Ca binding capacity. The implications of this atypical EPS matrix are currently under further investigation.

The current work provides a more complete understanding of CH₄ cycling in microbial mats and could have implications for the role of MA, sulfidogens, and microbial mats as gaseous and solid biosignatures.

Geological Society of America Abstracts with Programs. Vol. 58, No. 2, 2026

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