A H2/CO2-fed methanogenic mixed culture, inoculated from mesophilic anaerobic-digester sludge and cultivated in anoxic serum bottles, that was perturbed with sulfate and magnetite to test how a conductive Fe(II)/Fe(III) oxide reshapes sulfate-stressed anaerobic digestion. Vayena et al. (2026) compared a sulfate-free control with 0.6 and 1.2 g/L sulfate, with and without 10 g/L magnetite. At the moderate sulfate dose, magnetite increased methane production by 19% while retaining sulfate reduction and supporting a genome-resolved cooperative network among Methanoculleus methanogens, putative sulfate-reducing bacteria, Limnochordia homoacetogens, and Dethiobacteria syntrophic acetate oxidizers. Community genome-scale metabolic models for representative MAGs supported acetate, amino-acid, and carboxylate exchange among these guilds, but the paper explicitly leaves direct DIET validation for future experiments.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| Methanoculleus methanogenic MAGs — ontology label: Methanoculleus | NCBITaxon:45989 · TaxonMech · TraitMech |
SYNTROPHIC_PARTNER
ELECTRON_ACCEPTOR
CROSS_FEEDER
|
N/A |
|
|||
| putative sulfate-reducing MAGs — ontology label: Bacteria | NCBITaxon:2 · TaxonMech · TraitMech |
SYNTROPHIC_PARTNER
CROSS_FEEDER
|
N/A |
|
|||
| Limnochordia homoacetogenic MAGs — ontology label: Bacteria | NCBITaxon:2 · TaxonMech · TraitMech |
SYNTROPHIC_PARTNER
CROSS_FEEDER
|
N/A |
|
|||
| Dethiobacteria syntrophic acetate-oxidizing MAGs — ontology label: Bacteria | NCBITaxon:2 · TaxonMech · TraitMech |
SYNTROPHIC_PARTNER
ELECTRON_DONOR
CROSS_FEEDER
SECONDARY_FERMENTER
|
N/A |
|
|||
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.
Magnetite-enhanced methanogenesis under sulfate stress
At 0.6 g/L sulfate, 10 g/L magnetite increased cumulative methane by 19% relative to the sulfate-only treatment in five-day batch assays, without reducing sulfate consumption. This is partial improvement, not full sulfate-free recovery or rescue at 1.2 g/L sulfate. Separate abiotic tests showed sulfide removal and sulfur retained on magnetite, but elemental analysis did not resolve sulfur species and no abiotic hydrogen accumulation was detected. These results support toxicity mitigation as a contributing interpretation; they do not isolate its mediation of the methane response or demonstrate syntrophy or direct interspecies electron transfer. The four guilds identify an incomplete community context, not all organisms contributing to the bulk endpoints.
Participating Taxa: Methanoculleus methanogenic MAGs, putative sulfate-reducing MAGs, Limnochordia homoacetogenic MAGs, Dethiobacteria syntrophic acetate-oxidizing MAGs
Metabolites: sulfate (CHEBI:16189 · MediaIngredientMech · CMMMech), hydrogen sulfide (CHEBI:16136 · MediaIngredientMech · CMMMech), methane (CHEBI:16183 · MediaIngredientMech · CMMMech)
Biological Processes:
- methanogenesis (GO:0015948 · PathwayMech)
- dissimilatory sulfate reduction (GO:0019420 · PathwayMech)
Evidence
-
PMID:42231497 - SUPPORT (IN_VITRO)"the presence of magnetite reversed the sulfate-induced inhibition at 0.6 g/L sulfate, resulting in a 19% increase in CH4 production in MAGN_0.6 compared to SULF_0.6 "
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PMID:42231497 - SUPPORT (IN_VITRO)"Magnetite reduced dissolved sulfide species accumulation via precipitation and increased methane production by 19% at 0.6 g/L sulfate addition without limiting sulfate utilization. "
Acetate-centered four-guild redox cycling
CROSS_FEEDINGHYPOTHESIZED - condition-specific four-member GEMs predict acetate-centered exchange: a homoacetogen uses H2/CO2 and secretes acetate, a syntrophic acetate oxidizer returns H2/CO2, and a putative sulfate reducer oxidizes acetate while reducing sulfate, with the shared pool supporting hydrogenotrophic methanogenesis. Representatives are Methanoculleus DTU8, Halopseudomonas DTU25, Limnochordia DTU38 and Dethiobacteria DTU36, not every MAG in the four canonical guild placeholders. Models were gap-filled and curated for expected roles, constrained by measured reactor outputs, and analyzed using MICOM cooperative trade-off 0.7 and flux-space sampling. Agreement is stoichiometric feasibility under assumptions, not independent validation, measured partner flux or demonstrated DIET. One biological replicate per sequenced condition and relative MAG abundances cannot establish replicated absolute guild growth.
Participating Taxa: Methanoculleus methanogenic MAGs, putative sulfate-reducing MAGs, Limnochordia homoacetogenic MAGs, Dethiobacteria syntrophic acetate-oxidizing MAGs
Metabolites: dihydrogen (CHEBI:18276 · MediaIngredientMech · CMMMech), carbon dioxide (CHEBI:16526 · MediaIngredientMech · CMMMech), acetate (CHEBI:30089 · MediaIngredientMech · CMMMech), sulfate (CHEBI:16189 · MediaIngredientMech · CMMMech), methane (CHEBI:16183 · MediaIngredientMech · CMMMech)
Biological Processes:
- methanogenesis (GO:0015948 · PathwayMech)
- dissimilatory sulfate reduction (GO:0019420 · PathwayMech)
Evidence
-
PMID:42231497 - SUPPORT (COMPUTATIONAL)"The curated GEMs of the individual species were then integrated into multispecies community networks, one per condition, i.e., for CTRL, SULF_0.6, and MAGN_0.6. "
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PMID:42231497 - SUPPORT (COMPUTATIONAL)"Solution-space sampling further identified acetate as a central intermediate, produced and consumed by multiple guilds, with its turnover redistributing carbon and reducing equivalents across the community and thereby influencing methane formation. "
Model-predicted amino-acid and organic-acid exchange
CROSS_FEEDINGHYPOTHESIZED - flux-space sampling of the four representative GEMs predicts exchange of amino acids and organic acids, with the homoacetogen, acetate oxidizer and methanogen serving as modeled hubs and the putative sulfate reducer importing multiple amino acids. The reported heatmaps select mean exchange fluxes above 0.1 mmol/gDW/hour from feasible solutions; these are model summaries, not extracellular metabolomics or traced donor-recipient rates. Multiple solutions satisfy the imposed constraints, and regulation, protein capacity and kinetics are not resolved. These exchanges could support alternative metabolic routes, but actual necessity, universal mutualism and specific partner transfers remain untested.
Participating Taxa: Methanoculleus methanogenic MAGs, putative sulfate-reducing MAGs, Limnochordia homoacetogenic MAGs, Dethiobacteria syntrophic acetate-oxidizing MAGs
Metabolites: amino acid (CHEBI:33709 · MediaIngredientMech · CMMMech)
Biological Processes:
- biological process involved in interspecies interaction between organisms (GO:0044419 · PathwayMech)
Evidence
-
PMID:42231497 - SUPPORT (COMPUTATIONAL)"Flux-space sampling of the community model further provided a comprehensive view of feasible interspecies exchange patterns, not easily measurable in vivo (Supplementary material 3), suggesting extensive exchange of amino acids and short-chain organic acids among the four functional groups "
Associated Datasets
| Dataset | Type | Repository | Accession |
|---|---|---|---|
|
Sulfate-stressed magnetite anaerobic microbiome metagenomes
Genome-centric metagenomic reads and recovered MAGs from the sulfate-free control, 0.6 g/L sulfate treatment, and 0.6 g/L sulfate plus 10 g/L magnetite treatment. |
METAGENOMICS | NCBI_BIOPROJECT | PRJNA1242289 |
Knowledge gaps & discussions (2)
KNOWLEDGE_GAP OPEN Which members directly exchange electrons through magnetite or biological conductive structures in the sulfate-stressed anaerobic microbiome?
The Microbiome study links magnetite addition to a cooperative four-guild network and model-feasible metabolite exchange, but direct DIET validation was outside the experiment.
Attaches to: ecological_interactions#Acetate-centered four-guild redox cycling
1 evidence item(s)
Direct validation of DIET requires additional targeted experimental approaches beyond the scope of this study.
Records the source paper's own boundary around direct electron-transfer validation.
KNOWLEDGE_GAP OPEN Which processes mediate magnetite-associated methane improvement?
Keep zero arrows and preserve #914 backward-edge removal. Separate abiotic sulfide removal, replicated bulk methane response and single-replicate compositional metagenomics. Feasibility of role-curated and output-constrained GEMs does not independently verify partner flux. Retain the existing direct-DIET knowledge gap, #913 putative-SRB caveats and #915 restriction to MAGN_0.6. Myxococcota DTU51 lacks sulfate-reduction genes; do not silently promote it to a validated reducer. Source metadata and identity limits remain under #1574. Complete primary main text and figure captions read, not original figure pixels, separate supplements, raw data or executable models.
Attaches to: ecological_interactions#Magnetite-enhanced methanogenesis under sulfate stress, ecological_interactions#Acetate-centered four-guild redox cycling, ecological_interactions#Model-predicted amino-acid and organic-acid exchange
External Resources
| Name | Repository | Resource ID |
|---|---|---|
|
Primary publication DOI
Open-access Microbiome article reporting magnetite-enhanced methanogenesis, genome-centric metagenomics, and four-guild community genome-scale metabolic modeling under sulfate stress. |
OTHER | doi:10.1186/s40168-026-02443-4 |
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Environmental Factors
| Factor | Value | Unit |
|---|---|---|
| moderate sulfate stress | 0.6 | g/L sulfate |
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| magnetite conductive-material amendment | 10 | g/L magnetite |
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| H2/CO2 gas feed | 241 | H2/CO2 ratio |
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Growth Media
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