A northern Alaska wet sedge tundra microbial community studied across the permafrost thaw gradient, where iron-cycling Gammaproteobacteria - the heterotrophic Fe(III)-reducing Rhodoferax sp. and the chemoautotrophic Fe(II)-oxidizing Gallionella sp. - become numerically dominant during extended anaerobic thaw of transition-zone and permafrost soils. Functional gene abundance shows that Fe(III) reduction and Fe(II) oxidation increase in lockstep with benzoate degradation and pyruvate metabolism, supporting a carbon-cycling model in which acetate and benzoate are oxidized to CO2 coupled to Fe(III) reduction. Concurrent decreases in CH4-metabolism gene abundance suggest that dissimilatory Fe(III) reduction competitively suppresses acetoclastic methanogenesis under the reducing thaw conditions examined.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| heterotrophic Fe(III)-reducing Rhodoferax sp. — ontology label: Rhodoferax | NCBITaxon:28065 · TaxonMech · TraitMech |
PRIMARY_DEGRADER
CROSS_FEEDER
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DOMINANT |
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| chemoautotrophic Fe(II)-oxidizing Gallionella sp. — ontology label: Gallionella | NCBITaxon:96 · TaxonMech · TraitMech |
PRIMARY_PRODUCER
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DOMINANT |
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| wet sedge tundra methanogens — ontology label: Methanomicrobia | NCBITaxon:224756 · TaxonMech · TraitMech |
SECONDARY_FERMENTER
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N/A |
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Ecological Interactions
The graph shows only explicitly linked interaction participants. Community members without an asserted participant link are omitted; membership alone does not imply an interaction.
Fe(III) Reduction Coupled to Organic Acid Oxidation
HYPOTHESIZED - concurrent increases in iron-redox, benzoate-degradation and pyruvate-metabolism gene abundance support Rhodoferax-associated potential for organic-acid oxidation coupled to Fe(III) reduction during thaw. Gene copies do not establish pathway flux or the organism-resolved electron flow.
Participating Taxa: heterotrophic Fe(III)-reducing Rhodoferax sp.
Metabolites: acetate (CHEBI:30089 · MediaIngredientMech · CMMMech), benzoate (CHEBI:16150 · MediaIngredientMech · CMMMech), iron(3+) (CHEBI:29034 · MediaIngredientMech · CMMMech), iron(2+) (CHEBI:29033 · MediaIngredientMech · CMMMech), carbon dioxide (CHEBI:16526 · MediaIngredientMech · CMMMech)
HYPOTHESIZED - Fe(III) reduction could supply Fe(II) to Gallionella-associated oxidation; the proposed substrate connection was inferred from genomic patterns, not traced between partners.
HYPOTHESIZED - acetate use by iron reducers could limit substrate for acetoclastic methanogenesis; the study did not isolate acetate competition or measure its effect on methane flux.
Evidence
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PMID:37996661 - PARTIAL (COMPUTATIONAL)"the abundance of genes for Fe(III) reduction (e.g., MtrE) and Fe(II) oxidation (e.g., Cyc1) increased concurrently with genes for benzoate degradation and pyruvate metabolism, in which pyruvate is used to generate acetate that can be oxidized, along with benzoate, to CO2 when coupled with Fe(III) reduction"
Candidate Iron-Reduction Suppression of Acetoclastic Methanogenesis
HYPOTHESIZED - declining methane-metabolism gene abundance during thaw was interpreted as consistent with iron reducers competing for acetate. This is not direct evidence that Rhodoferax suppressed methane production or caused the methanogen genomic changes.
Participating Taxa: heterotrophic Fe(III)-reducing Rhodoferax sp., wet sedge tundra methanogens
Metabolites: acetate (CHEBI:30089 · MediaIngredientMech · CMMMech), methane (CHEBI:16183 · MediaIngredientMech · CMMMech)
Biological Processes:
- methane biosynthetic process (GO:0015948 · PathwayMech)
Evidence
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PMID:37996661 - PARTIAL (COMPUTATIONAL)"dissimilatory Fe(III) reduction suppresses acetoclastic methanogenesis under reducing conditions"
Fe(II) Oxidation by Chemoautotrophic Gallionella
HYPOTHESIZED - Gallionella abundance and iron-oxidation gene patterns suggest Fe(II) oxidation could regenerate Fe(III) for heterotrophic iron reduction. The authors infer suboxic conditions; oxygen availability and reciprocal iron transfer were not directly resolved by these genomic observations.
Participating Taxa: chemoautotrophic Fe(II)-oxidizing Gallionella sp., heterotrophic Fe(III)-reducing Rhodoferax sp.
Metabolites: iron(2+) (CHEBI:29033 · MediaIngredientMech · CMMMech), iron(3+) (CHEBI:29034 · MediaIngredientMech · CMMMech)
HYPOTHESIZED - Gallionella-associated Fe(II) oxidation could regenerate the Fe(III) acceptor for organic-acid oxidation; this proposed feedback lacks direct flux or partner-removal validation.
Evidence
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PMID:37996661 - PARTIAL (COMPUTATIONAL)"the abundance of genes for Fe(III) reduction (e.g., MtrE) and Fe(II) oxidation (e.g., Cyc1) increased concurrently"
Knowledge gaps & discussions (1)
KNOWLEDGE_GAP OPEN Do direct redox and carbon-flux measurements confirm iron cycling and methane suppression?
PMID:37996661 reports genomic abundance changes from thaw incubations, not resolved iron/carbon flux. Oxygen conditions were inferred despite nitrogen purging. Acetate perturbations, methane production measurements and partner-specific iron transfer are needed to distinguish the proposed mechanisms. GO:0006826 describes ion transport rather than the redox reactions curated here.
Attaches to: ecological_interactions#Fe(III) Reduction Coupled to Organic Acid Oxidation, ecological_interactions#Candidate Iron-Reduction Suppression of Acetoclastic Methanogenesis, ecological_interactions#Fe(II) Oxidation by Chemoautotrophic Gallionella
Environmental Factors
| Factor | Value | Unit |
|---|---|---|
| Anaerobic thaw incubation | 30 days at 4 deg C under reducing conditions | N/A |
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| Permafrost depth gradient | active-layer / transition-zone / permafrost | N/A |
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Growth Media
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