identifier: traitmech:000039
label: dissimilatory metal reduction
definition: An anaerobic respiratory metabolism in which an organism conserves energy
  for growth by coupling the oxidation of organic matter or hydrogen to the reduction
  of a metal (e.g. Fe(III), Mn(IV)) as a terminal electron acceptor.
definition_source: DOI:10.1128/mr.55.2.259-287.1991
trait_category: METABOLISM
term_kind: CLASS
mapping_status: REVIEWED
parent_traits:
- METPO:1000802
synonyms:
- synonym_text: dissimilatory metal-ion reduction
  synonym_type: RELATED_SYNONYM
  source: DOI:10.1128/mr.55.2.259-287.1991
evidence:
- reference: DOI:10.1128/mr.55.2.259-287.1991
  snippet: The oxidation of organic matter coupled to the reduction of Fe(III) or
    Mn(IV) is one of the most important biogeochemical reactions in aquatic sediments,
    soils, and groundwater
  notes: Lovley review establishes dissimilatory metal (Fe(III)/Mn(IV)) reduction
    as energy-conserving anaerobic respiration; parent of the metal-specific reduction
    sub-variants.
- reference: PMID:7826009
  notes: Nealson & Saffarini, "Iron and manganese in anaerobic respiration", supports
    metals as terminal electron acceptors in anaerobic respiration.
canonical_examples:
- taxon_id: NCBITaxon:35554
  taxon_label: Geobacter sulfurreducens
  note: "Model dissimilatory metal reducer; respires Fe(III)/Mn(IV) via extracellular electron transfer and conductive pili (type strain PCA)."
  reference: PMID:14671304
causal_graphs:
- graph_id: metal_reduction_anaerobic_respiration
  title: Dissimilatory metal reduction couples organic oxidation to metal respiration
  description: Evidence-backed causal sketch linking oxidation of organic matter or
    hydrogen to reduction of metal terminal electron acceptors.
  nodes:
  - node_id: metal_reduction_trait
    label: dissimilatory metal reduction
    node_type: TRAIT
    grounding: traitmech:000039
    description: Energy-conserving anaerobic respiration with a metal acceptor.
  - node_id: metal_terminal_acceptor
    label: terminal electron acceptor
    node_type: CHEMICAL
    grounding: METPO:1007504
    description: Fe(III) or Mn(IV) oxide acting as terminal electron acceptor.
  - node_id: anaerobic_respiration
    label: anaerobic respiration
    node_type: BIOLOGICAL_PROCESS
    grounding: GO:0009061
    description: Energy-conserving respiration with non-O2 acceptor.
  - node_id: organic_matter_oxidation
    label: organic compound oxidation
    node_type: BIOLOGICAL_PROCESS
    description: Oxidation of organic compounds providing electrons for metal reduction.
  - node_id: fe3_reduction
    label: Fe(III) reduction
    node_type: BIOLOGICAL_PROCESS
    description: Reduction of ferric iron to ferrous iron.
  - node_id: mtrcab_complex
    label: MtrCAB outer-membrane complex
    node_type: GENE_OR_PROTEIN
    description: Outer-membrane porin-cytochrome complex forming an electron-transfer
      conduit.
  - node_id: extracellular_acceptor
    label: extracellular electron acceptor
    node_type: CHEMICAL
    description: Insoluble or extracellular acceptor receiving respiratory electrons.
  - node_id: flavin_shuttle
    label: flavin electron shuttle
    node_type: CHEMICAL
    description: Redox-active flavin mediating electron transfer to distant substrates.
  - node_id: insoluble_metal_substrate
    label: oxidized insoluble metal
    node_type: CHEMICAL
    description: Oxidized insoluble/crystalline metal serving as respiratory substrate.
  - node_id: anaerobic_subsurface_env
    label: anaerobic subsurface environment
    node_type: ENVIRONMENTAL_FACTOR
    description: Anaerobic subsurface where Fe(III) is present as insoluble/crystalline
      forms.
  edges:
  - subject: metal_terminal_acceptor
    predicate: enables
    object: metal_reduction_trait
    description: Metal-ion acceptors enable energy-conserving anaerobic respiration
      on metals.
    evidence:
    - reference: DOI:10.1128/mr.55.2.259-287.1991
      notes: Lovley establishes dissimilatory metal (Fe(III)/Mn(IV)) reduction as
        energy-conserving anaerobic respiration.
    predicate_id: RO:0002327
  - subject: metal_reduction_trait
    predicate: participates in
    object: anaerobic_respiration
    description: Metal reduction is a class of anaerobic respiration.
    evidence:
    - reference: PMID:7826009
      notes: Nealson & Saffarini place iron and manganese as terminal electron acceptors
        within anaerobic respiration.
    predicate_id: biolink:participates_in
  - subject: organic_matter_oxidation
    predicate: donates electrons to
    object: fe3_reduction
    description: Oxidation of organic compounds donates electrons to Fe(III) reduction
      in metal-reducing bacteria.
    evidence:
    - reference: DOI:10.1007/s11783-019-1173-9
      notes: FeRB transfers electrons to Fe(III), Fe(III) is reduced to Fe(II), and
        organic compounds are mineralized (Jiang et al., 2019); general respiratory
        coupling.
    predicate_id: METPO:2007403
  - subject: mtrcab_complex
    predicate: transfers electrons to
    object: extracellular_acceptor
    description: The MtrCAB outer-membrane complex creates a pathway transferring
      electrons to an extracellular acceptor.
    evidence:
    - reference: DOI:10.1128/aem.00044-24
      notes: The outer membrane complex MtrCAB creates a pathway that transfers electrons
        to an extracellular acceptor (Hsu et al., 2024); generalized EET conduit role.
    predicate_id: METPO:2007403
  - subject: flavin_shuttle
    predicate: facilitates electron transfer to
    object: extracellular_acceptor
    description: Flavin shuttles facilitate electron transfer to substrates distant
      from the cell surface.
    evidence:
    - reference: DOI:10.3390/fermentation11070381
      notes: Redox-active small molecules (flavins) facilitate electron transfer to
        substrates distant from the cell surface (Soares et al., 2025); mediated EET
        especially where metal oxides are spatially inaccessible.
  - subject: insoluble_metal_substrate
    predicate: serves as respiratory substrate for
    object: metal_reduction_trait
    description: Oxidized insoluble metals serve as an abundant respiratory substrate
      for metal reduction.
    evidence:
    - reference: DOI:10.1128/aem.00044-24
      notes: Oxidized, insoluble metals are an abundant electron acceptor that microbes
        could utilize as a respiratory substrate (Hsu et al., 2024); trait-defining.
  - subject: anaerobic_subsurface_env
    predicate: provides condition for
    object: fe3_reduction
    description: Fe(III) reduction occurs under anaerobic subsurface conditions where
      Fe(III) is insoluble/crystalline.
    evidence:
    - reference: DOI:10.1007/s11783-019-1173-9
      notes: Fe(III) has solubility ~10^-9 M at neutral pH and is generally present
        as insoluble or crystalline forms under anaerobic subsurface environments
        (Jiang et al., 2019); environmental/chemical constraint.
curation_history:
- timestamp: '2026-05-31T00:00:00Z'
  curator: claude
  action: PROPOSED_FROM_RESEARCH
  changes: Minted intermediate axis class (dissimilatory metal reduction) under anaerobic
    respiration (METPO:1000802) to parent dissimilatory iron reduction.
  llm_assisted: true
- timestamp: '2026-06-10T14:00:00Z'
  curator: claude
  action: CURATED_CAUSAL_GRAPH
  changes: Added evidence-backed causal graph (metal-acceptor anaerobic respiration)
    with METPO/GO node groundings and RO/biolink predicate groundings; promoted PROPOSED
    to REVIEWED.
  llm_assisted: true
- timestamp: '2026-06-23T00:00:00Z'
  curator: claude
  action: ENRICH_CAUSAL_GRAPH
  changes: Added 5 evidence-backed generic edges (7 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
    (METPO:2007403×2).
  llm_assisted: true