Two simplified methanogenic consortia (DIETsimp) constructed by top-down selection from cow manure combined with paddy soil or marine sediment inocula for high-efficiency conversion of lignocellulose to methane via direct interspecies electron transfer (DIET). Metagenomic analysis identified Methanosarcina mazei, capable of accepting electrons via DIET, as the dominant archaeon, and the electroactive bacteria Sphaerochaeta globosa and Clostridium aceticum as the dominant bacteria. The proposed DIET-based methanogenic pathway has S. globosa and C. aceticum metabolizing intermediates (xylose, glucose, pyruvate, acetate) and transferring electrons to M. mazei for reduction of CO2 to methane. Both consortia shortened methanogenesis periods and increased methane production rates relative to conventional anaerobic digestion.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| Methanosarcina mazei | NCBITaxon:2209 · TaxonMech · TraitMech |
SYNTROPHIC_PARTNER
ELECTRON_ACCEPTOR
ELECTROTROPH
|
N/A |
|
|||
| Sphaerochaeta globosa | NCBITaxon:1131703 · TaxonMech · TraitMech |
PRIMARY_DEGRADER
ELECTRON_DONOR
ELECTROGEN
SYNTROPHIC_PARTNER
|
N/A |
|
|||
| Clostridium aceticum — ontology label: Andreesenella acetica | NCBITaxon:84022 · TaxonMech · TraitMech |
PRIMARY_DEGRADER
ELECTRON_DONOR
ELECTROGEN
SYNTROPHIC_PARTNER
|
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.
Proposed S. globosa to M. mazei DIET Syntrophy
SYNTROPHYHYPOTHESIZED - Sphaerochaeta globosa is proposed to participate in direct electron delivery to Methanosarcina mazei in the two simplified lignocellulose-digesting consortia. The abstract links the dominant bacterial pair collectively to intermediates including xylose, glucose, pyruvate and acetate; it does not assign every substrate or flux separately to this donor. Community conductivity, cytochrome-associated spectra and metagenomic profiles support the model but do not distinguish this route from hydrogen/formate transfer, establish obligate donor dependence, or trace direct electron delivery by this particular partner.
Source Taxon: Sphaerochaeta globosa
Target Taxon: Methanosarcina mazei
Metabolites: xylose (CHEBI:18222 · MediaIngredientMech · CMMMech), D-glucose (CHEBI:17634 · MediaIngredientMech · CMMMech), pyruvate (CHEBI:15361 · MediaIngredientMech · CMMMech), acetate (CHEBI:30089 · MediaIngredientMech · CMMMech), carbon dioxide (CHEBI:16526 · MediaIngredientMech · CMMMech), methane (CHEBI:16183 · MediaIngredientMech · CMMMech)
HYPOTHESIZED - direct electron delivery by Sphaerochaeta globosa could supply reducing equivalents for the proposed M. mazei CO2-to-methane step. The available abstract proposes this contribution but does not trace donor-specific electrons, establish the carrier, or selectively perturb that route; this arrow does not assert a dependency between the two bacterial donors.
Evidence
-
PMID:42229598 - PARTIAL (OTHER)"S. globosa and C. aceticum metabolized intermediates (e.g. xylose, glucose, pyruvate and acetate) and transferred electrons to M. mazei for the reduction of CO2 to methane"
Proposed C. aceticum to M. mazei DIET Syntrophy
SYNTROPHYHYPOTHESIZED - Clostridium aceticum (Andreesenella acetica) is proposed to participate in direct electron delivery to Methanosarcina mazei in the two simplified lignocellulose-digesting consortia. The abstract links the dominant bacterial pair collectively to intermediates including xylose, glucose, pyruvate and acetate; it does not assign every substrate or flux separately to this donor. Community conductivity, cytochrome-associated spectra and metagenomic profiles support the model but do not distinguish this route from hydrogen/formate transfer, establish obligate donor dependence, or trace direct electron delivery by this particular partner.
Source Taxon: Clostridium aceticum
Target Taxon: Methanosarcina mazei
Metabolites: xylose (CHEBI:18222 · MediaIngredientMech · CMMMech), D-glucose (CHEBI:17634 · MediaIngredientMech · CMMMech), pyruvate (CHEBI:15361 · MediaIngredientMech · CMMMech), acetate (CHEBI:30089 · MediaIngredientMech · CMMMech), carbon dioxide (CHEBI:16526 · MediaIngredientMech · CMMMech), methane (CHEBI:16183 · MediaIngredientMech · CMMMech)
HYPOTHESIZED - direct electron delivery by Clostridium aceticum (Andreesenella acetica) could supply reducing equivalents for the proposed M. mazei CO2-to-methane step. The available abstract proposes this contribution but does not trace donor-specific electrons, establish the carrier, or selectively perturb that route; this arrow does not assert a dependency between the two bacterial donors.
Evidence
-
PMID:42229598 - PARTIAL (OTHER)"S. globosa and C. aceticum metabolized intermediates (e.g. xylose, glucose, pyruvate and acetate) and transferred electrons to M. mazei for the reduction of CO2 to methane"
Proposed M. mazei CO2 Reduction to Methane
HYPOTHESIZED - the proposed model assigns CO2 reduction to methane to dominant Methanosarcina mazei using electrons attributed to the bacterial partners. This is an intrinsic methanogen step, not a separate whole-community syntrophic relationship. Lower-pH conductivity and enhanced cytochrome-associated electrochemical FTIR signals are positive community-level observations consistent with the DIET model, but do not measure the M. mazei-specific contribution or exclude alternative electron carriers and methanogenic routes. Reported methane-performance improvements are not selective tests of this mechanism.
Source Taxon: Methanosarcina mazei
Metabolites: carbon dioxide (CHEBI:16526 · MediaIngredientMech · CMMMech), methane (CHEBI:16183 · MediaIngredientMech · CMMMech)
Biological Processes:
- methanogenesis (GO:0015948 · PathwayMech)
Evidence
-
PMID:42229598 - PARTIAL (OTHER)"transferred electrons to M. mazei for the reduction of CO2 to methane"
-
PMID:42229598 - PARTIAL (IN_VITRO)"Lowering pH dramatically increased conductivity of both DIETsimp"
Knowledge gaps & discussions (1)
KNOWLEDGE_GAP OPEN Do the proposed S. globosa-to-M. mazei and C. aceticum-to-M. mazei routes involve direct electron transfer rather than hydrogen/formate mediation, and how much methane do they support?
The complete primary abstract contains positive pH-dependent conductivity, cytochrome-associated spectral and metagenomic observations, but explicitly calls the methanogenic route proposed. Full Methods/Results, donor-resolved tracing and selective perturbations were not available in this review. Both existing arrows are retained as hypotheses connecting parallel donor proposals to the methanogen's intrinsic step; neither makes one donor relationship depend on the other. This corrects the older no-downstream wording without asserting new structure. Neutral-red-mediated electron delivery or other-system demonstrations must not be imported as exact-system evidence. Non-graph taxon roles, mechanism language and performance-versus-protocol distinctions remain in #1373.
Attaches to: ecological_interactions#Proposed S. globosa to M. mazei DIET Syntrophy, ecological_interactions#Proposed C. aceticum to M. mazei DIET Syntrophy, ecological_interactions#Proposed M. mazei CO2 Reduction to Methane
1 evidence item(s)
during anaerobic digestion of lignocellulose that S. globosa and C. aceticum metabolized intermediates
This excerpt belongs to the abstract's explicitly proposed mechanism. It does not invalidate the positive community measurements, but cannot establish partner-specific direct transfer or its share of methane production.
Growth Media
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