identifier: METPO:1000844
label: Methanogenesis
definition: A metabolism in which methane is produced as the primary end product through
  the reduction of carbon-containing compounds, formate, methanol, or acetate, exclusively
  performed by methanogenic archaea under strictly anaerobic conditions.
definition_source: DOI:10.1146/annurev-micro-011720-122807
trait_category: METABOLISM
term_kind: CLASS
mapping_status: REVIEWED
parent_traits:
- METPO:1000060
synonyms:
- synonym_text: Biological methanation
  synonym_type: RELATED_SYNONYM
  source: metpo.owl
- synonym_text: Biomethanation
  synonym_type: RELATED_SYNONYM
  source: metpo.owl
- synonym_text: Carbonate respiration
  synonym_type: RELATED_SYNONYM
  source: metpo.owl
created_by: Luke Wang
evidence:
- reference: DOI:10.1146/annurev-micro-011720-122807
  snippet: from CO2 and H2 to methane
  notes: Supports hydrogenotrophic methanogenesis as a methane-producing archaeal
    pathway.
- reference: DOI:10.1021/acs.biochem.9b00164
  snippet: catalyzes the reversible reduction of methyl-coenzyme M
  notes: Supports methyl-coenzyme M reductase as the terminal methane-forming enzyme.
canonical_examples:
- taxon_id: NCBITaxon:2190
  taxon_label: Methanocaldococcus jannaschii
  note: "Archetypal hydrogenotrophic methanogen (4 H2 + CO2 -> CH4 + 2 H2O); first archaeal genome sequenced."
  reference: https://pmc.ncbi.nlm.nih.gov/articles/PMC6616113/
causal_graphs:
- graph_id: methanogenesis_c1_reduction
  title: Methanogenesis C1 reduction mechanism
  description: Evidence-backed causal sketch linking anoxic C1 reduction, methyl-coenzyme
    M reductase, and methane formation.
  nodes:
  - node_id: methanogenesis_trait
    label: Methanogenesis
    node_type: TRAIT
    grounding: METPO:1000844
    description: Methane-producing archaeal metabolism.
  - node_id: anoxic_habitat
    label: anoxic habitat
    node_type: ENVIRONMENTAL_FACTOR
    description: Oxygen-depleted condition where hydrogenotrophic methanogenesis occurs.
  - node_id: carbon_dioxide
    label: carbon dioxide
    node_type: CHEMICAL
    grounding: CHEBI:16526
    description: C1 substrate reduced during hydrogenotrophic methanogenesis.
  - node_id: molecular_hydrogen
    label: molecular hydrogen
    node_type: CHEMICAL
    grounding: CHEBI:18276
    description: Electron donor for hydrogenotrophic methanogenesis.
  - node_id: methyl_coenzyme_m_reductase
    label: methyl-coenzyme M reductase
    node_type: GENE_OR_PROTEIN
    description: Nickel F430 enzyme catalyzing the terminal methane-forming step.
    grounding: UniProtKB:A0A099T5Q9
  - node_id: coenzyme_f430
    label: coenzyme F430
    node_type: CHEMICAL
    description: Nickel-containing prosthetic group of methyl-coenzyme M reductase.
    grounding: CHEBI:28265
  - node_id: methane
    label: methane
    node_type: CHEMICAL
    grounding: CHEBI:16183
    description: Primary reduced carbon end product.
  - node_id: mcr_gene_cluster
    label: mcrABG gene cluster
    node_type: GENE_OR_PROTEIN
    description: Conserved gene cluster encoding the methyl-coenzyme M reductase complex.
  - node_id: acetoclastic_methanogenesis
    label: acetoclastic methanogenesis
    node_type: PATHWAY
    description: Methanogenic pathway splitting acetate into methane and CO2.
  - node_id: acetate
    label: acetate
    node_type: CHEMICAL
    grounding: CHEBI:30089
    description: C2 substrate for acetoclastic methanogenesis.
  - node_id: methyl_based_methanogenesis
    label: methyl-based methanogenesis
    node_type: PATHWAY
    description: Methanogenic pathway using methylated compounds as substrate.
  - node_id: methylated_compounds
    label: methylated compounds
    node_type: CHEMICAL
    description: Methyl-bearing substrates (e.g. methanol, methylamines) feeding methyl-based
      methanogenesis.
  - node_id: coenzyme_b
    label: coenzyme B
    node_type: CHEMICAL
    description: Thiol cofactor (CoB) required in the terminal methane-forming reaction.
  - node_id: coenzyme_m
    label: coenzyme M
    node_type: CHEMICAL
    description: Methyl-carrier cofactor (CoM) onto which methyl groups are transferred
      to form methyl-CoM.
  - node_id: coenzyme_f420
    label: coenzyme F420 (F420H2)
    node_type: CHEMICAL
    description: Reduced deazaflavin electron carrier donating electrons for C1 reduction
      steps.
  edges:
  - subject: methanogenesis_trait
    predicate: occurs in
    object: anoxic_habitat
    description: Hydrogenotrophic methanogenesis is associated with anoxic habitats.
    evidence:
    - reference: DOI:10.1146/annurev-micro-011720-122807
      snippet: terminal step of microbial biomass degradation in anoxic habitats
      notes: Review places hydrogenotrophic methanogenesis in anoxic microbial biomass
        degradation.
    predicate_id: biolink:occurs_in
  - subject: carbon_dioxide
    predicate: reduced with electron donor
    object: molecular_hydrogen
    description: Carbon dioxide is reduced using electrons derived from hydrogen.
    evidence:
    - reference: DOI:10.1146/annurev-micro-011720-122807
      snippet: from CO2 and H2 to methane
      notes: Supports the CO2 plus H2 substrate relationship.
  - subject: methyl_coenzyme_m_reductase
    predicate: has prosthetic group
    object: coenzyme_f430
    description: Methyl-coenzyme M reductase contains nickel coenzyme F430.
    evidence:
    - reference: DOI:10.1021/acs.biochem.9b00164
      snippet: harbors the nickel(I) hydrocorphin coenzyme F-430
      notes: Supports F430 as the prosthetic group of the enzyme.
  - subject: methyl_coenzyme_m_reductase
    predicate: catalyzes formation of
    object: methane
    description: Methyl-coenzyme M reductase catalyzes the terminal methane-forming
      reaction.
    evidence:
    - reference: DOI:10.1021/acs.biochem.9b00164
      snippet: catalyzes the reversible reduction of methyl-coenzyme M
      notes: Source describes methane formation by methyl-coenzyme M reductase.
    predicate_id: biolink:catalyzes
  - subject: methanogenesis_trait
    predicate: produces
    object: methane
    description: The defining output of methanogenesis is methane.
    evidence:
    - reference: DOI:10.1146/annurev-micro-011720-122807
      snippet: from CO2 and H2 to methane
      notes: Supports methane as the reduced product of hydrogenotrophic methanogenesis.
    predicate_id: METPO:2000202
  - subject: mcr_gene_cluster
    predicate: enables
    object: methyl_coenzyme_m_reductase
    description: The mcrABG gene cluster encodes the methyl-coenzyme M reductase complex.
    evidence:
    - reference: DOI:10.1128/mmbr.00024-22
      notes: A key genetic requirement across these pathways is the presence of mcrABG.
    predicate_id: RO:0002327
  - subject: acetate
    predicate: serves as substrate for
    object: acetoclastic_methanogenesis
    description: Acetate is the substrate split to methane and CO2 in acetoclastic
      methanogenesis.
    evidence:
    - reference: DOI:10.1007/s00253-023-12700-3
      notes: acetoclastic (splitting acetate to CH4 and CO2).
  - subject: methylated_compounds
    predicate: serves as substrate for
    object: methyl_based_methanogenesis
    description: Methylated compounds are the substrates for methyl-based methanogenesis.
    evidence:
    - reference: DOI:10.1007/s00253-023-12700-3
      notes: methylotrophic (using methylated compounds).
  - subject: coenzyme_b
    predicate: is required for
    object: methane
    description: Coenzyme B reacts with methyl-CoM in the terminal step to yield methane.
    evidence:
    - reference: DOI:10.1128/mmbr.00024-22
      notes: methyl-CoM reacts with coenzyme B (CoB) to yield methane.
  - subject: coenzyme_m
    predicate: carries methyl group in
    object: methanogenesis_trait
    description: Methyltransferases transfer methyl groups to coenzyme M to form methyl-CoM.
    evidence:
    - reference: DOI:10.1128/mmbr.00024-22
      notes: methyltransferases transfer methyl groups ultimately to CoM to form methyl-CoM.
  - subject: coenzyme_f420
    predicate: donates electrons to
    object: carbon_dioxide
    description: Reduced coenzyme F420 donates electrons for reduction of C1 intermediates
      derived from CO2.
    evidence:
    - reference: DOI:10.3389/fmicb.2023.1296008
      notes: Reduced coenzyme F420 (F420H2) donates electrons for reductions of methenyl/methylene
        intermediates.
    predicate_id: METPO:2007403
curation_history:
- timestamp: '2026-05-05T01:35:46.914643+00:00'
  curator: seed_from_metpo
  action: SEEDED_FROM_METPO
  changes: imported from data/raw/metpo.owl (CLASS)
  llm_assisted: false
- timestamp: '2026-05-07T00:00:00-07:00'
  curator: codex
  action: ADDED_CAUSAL_GRAPH
  changes: Added DOI-backed causal graph for anoxic C1 reduction to methane and the
    methyl-coenzyme M reductase terminal step.
  llm_assisted: true
- timestamp: '2026-05-20T03:35:30Z'
  curator: claude
  action: GROUND_CAUSAL_PREDICATES
  changes: Grounded 1 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv
    (METPO:2000202×1).
  llm_assisted: true
- timestamp: '2026-05-24T05:05:14Z'
  curator: claude
  action: GROUND_CAUSAL_NODES
  changes: Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv
    (UniProtKB:A0A099T5Q9×1).
  llm_assisted: true
- timestamp: '2026-05-26T05:00:48Z'
  curator: claude
  action: RENAME_PREDICATE_LABELS
  changes: 'Renamed 1 causal-edge predicate label(s) to align with existing groundings:
    occurs under → occurs in ×1.'
  llm_assisted: true
- timestamp: '2026-05-26T05:00:50Z'
  curator: claude
  action: GROUND_CAUSAL_PREDICATES
  changes: Grounded 1 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv
    (biolink:occurs_in×1).
  llm_assisted: true
- timestamp: '2026-06-13T21:03:26Z'
  curator: claude
  action: GROUND_CAUSAL_PREDICATES
  changes: Grounded 1 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv
    (biolink:catalyzes×1).
  llm_assisted: true
- timestamp: '2026-06-14T05:51:46Z'
  curator: claude
  action: GROUND_CAUSAL_NODES
  changes: Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv
    (CHEBI:28265×1).
  llm_assisted: true
- timestamp: '2026-06-17T04:09:44Z'
  curator: claude
  action: REMOVE_REDUNDANT_SYNONYM
  changes: Removed 1 synonym(s) whose text duplicated the label (seeder redundancy;
    no information lost).
  llm_assisted: true
- timestamp: '2026-06-23T00:00:00Z'
  curator: claude
  action: ENRICH_CAUSAL_GRAPH
  changes: Added 6 evidence-backed generic edges (8 new nodes) from the deep-research
    report.
  llm_assisted: true
- timestamp: '2026-06-24T17:21:12Z'
  curator: claude
  action: GROUND_CAUSAL_PREDICATES
  changes: Grounded 2 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv
    (RO:0002327×1, METPO:2007403×1).
  llm_assisted: true