An anoxic, methanogenic enrichment culture defining "lithosyntrophy," an obligate syntrophic interaction in which the electrons driving hydrogenotrophic methanogenesis originate from an inorganic compound. Candidatus Phosphitivorax anaerolimi Phox-21 oxidizes phosphite (oxidation state +3) to phosphate coupled to hydrogenogenesis, in an obligate energetic dependency on a hydrogenotrophic methanogen, Methanoculleus sp. Electrons derived from phosphite drive H2 production via an electron-confurcating hydrogenase; the methanogen consumes the H2 to keep the reaction thermodynamically favorable, establishing interspecies electron transfer that links the phosphorus and carbon redox cycles in anoxic ecosystems.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| Candidatus Phosphitivorax anaerolimi Phox-21 — ontology label: Candidatus Phosphitivorax anaerolimi | NCBITaxon:1918507 · TaxonMech · TraitMech |
SYNTROPHIC_PARTNER
ELECTRON_DONOR
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N/A |
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| Methanoculleus sp. — ontology label: Methanoculleus | NCBITaxon:45989 · TaxonMech · TraitMech |
SYNTROPHIC_PARTNER
ELECTRON_ACCEPTOR
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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.
Phox-21 Phosphite-Driven Hydrogenogenesis
SYNTROPHYPhox-21 oxidizes phosphite to phosphate coupled to H2 production in the methanogenic enrichment. Preserve the experimentally supported lithosyntrophic process. PARTIAL - The specific HndABCD electron-confurcating hydrogenase/Rnf energy-conservation mechanism is a model based on annotation, abundant proteins and thermodynamic calculations, not direct enzyme perturbation. Acetate supports mixotrophic biomass assimilation and is not the demonstrated source of methane.
Source Taxon: Candidatus Phosphitivorax anaerolimi Phox-21
Target Taxon: Methanoculleus sp.
Metabolites: hydrogen (H2) (CHEBI:18276 · MediaIngredientMech · CMMMech)
Phox-21 hydrogenogenesis supplies the H2 carrier that is consumed by the hydrogenotrophic Methanoculleus partner.
Evidence
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PMID:41811448 - SUPPORT (IN_VITRO)"we describe "lithosyntrophy," a mode of syntrophic interaction in which electrons that drive hydrogenotrophic methanogenesis originate from an inorganic compound rather than from the canonical organic substrates."
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PMID:41811448 - PARTIAL (COMPUTATIONAL)"In this pathway, electrons derived from phosphite drive H2 production via an electron-confurcating hydrogenase."
Lithosyntrophic interspecies H2 transfer
SYNTROPHYPhox-21 supplies phosphite-derived reducing equivalents to Methanoculleus as H2. Methanogenic phosphite oxidation was inhibited by BES and by excess H2; growth and oxidation were restored with hydrogenotrophic sulfate reducer G11 in BES. These experiments support a required low-H2 sink under tested conditions, not universal dependence on this exact methanogen. Net chemical phosphite oxidation remains exergonic; the proposed H2-sensitive bottleneck concerns intracellular electron transfer and energy conservation.
Source Taxon: Candidatus Phosphitivorax anaerolimi Phox-21
Target Taxon: Methanoculleus sp.
Metabolites: hydrogen (H2) (CHEBI:18276 · MediaIngredientMech · CMMMech)
Consumption of lithosyntrophic H2 by Methanoculleus sp. drives the hydrogenotrophic methanogenesis endpoint.
Evidence
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PMID:41811448 - SUPPORT (IN_VITRO)"Candidatus Phosphitivorax anaerolimi Phox-21 oxidizes phosphite (HPO32-, oxidation state +3) to phosphate coupled to hydrogenogenesis in an obligate energetic dependency on a hydrogenotrophic methanogen, Methanoculleus sp."
Methanoculleus Hydrogenotrophic Methanogenesis
SYNTROPHYMethanoculleus consumes H2 and produces methane, providing the hydrogen sink for Phox-21 in the methanogenic enrichment. Phosphite oxidation and methane production were approximately stoichiometric; isotope and isolate-substrate tests support H2/CO2-derived rather than acetate-derived methane. Low H2 enables the proposed intracellular energy-conserving pathway, not an otherwise endergonic net phosphite-oxidation reaction. The syntrophic pair is embedded in an enrichment, not a demonstrated two-member pure culture.
Source Taxon: Methanoculleus sp.
Target Taxon: Candidatus Phosphitivorax anaerolimi Phox-21
Metabolites: hydrogen (H2) (CHEBI:18276 · MediaIngredientMech · CMMMech), methane (CHEBI:16183 · MediaIngredientMech · CMMMech)
Biological Processes:
- methanogenesis (GO:0015948 · PathwayMech)
Evidence
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PMID:41811448 - SUPPORT (IN_VITRO)"a mode of syntrophic interaction in which electrons that drive hydrogenotrophic methanogenesis originate from an inorganic compound rather than from the canonical organic substrates"
Knowledge gaps & discussions (1)
KNOWLEDGE_GAP OPEN How should the demonstrated hydrogen-sink dependence be represented as feedback?
Preserve both donor-to-H2-to-methanogenesis arrows. Primary full text supplies BES inhibition, excess-H2 inhibition, measured low H2 and G11 rescue: a sink-to-donor feedback candidate remains unrepresented in downstream and is tracked in #1700. No new arrow without the scoped Edison workflow. HndABCD/Rnf remains a proposed intracellular model, while physiological dependence is experimentally supported. Acetate/sulfide medium contained seven taxa (Phox-21 >98%); cysteine medium contained sixteen. Non-graph two-member and taxonomy notes are not certified and remain #1701.
Attaches to: ecological_interactions#Phox-21 Phosphite-Driven Hydrogenogenesis, ecological_interactions#Lithosyntrophic interspecies H2 transfer, ecological_interactions#Methanoculleus Hydrogenotrophic Methanogenesis
2 evidence item(s)
Candidatus Phosphitivorax anaerolimi Phox-21 oxidizes phosphite (HPO32-, oxidation state +3) to phosphate coupled to hydrogenogenesis in an obligate energetic dependency on a hydrogenotrophic methanogen, Methanoculleus sp.
Preserves the reported positive H2-mediated partnership; the full paper bounds the requirement using inhibition and an alternative hydrogen-consuming partner.
In this pathway, electrons derived from phosphite drive H2 production via an electron-confurcating hydrogenase.
The abstract summarizes the proposed hydrogenase route; full Results call it a metaproteomic and thermodynamic model, not an enzyme-specific causal experiment.
Growth Media
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