identifier: METPO:1000610
label: microaerotolerant
definition: An oxygen preference that tolerates low levels of molecular oxygen (O₂)
  without requiring it.
definition_source: DOI:10.1016/j.biortech.2011.02.011
trait_category: ENVIRONMENT
term_kind: CLASS
mapping_status: REVIEWED
parent_traits:
- METPO:1000601
evidence:
- reference: DOI:10.1016/j.biortech.2011.02.011
  snippet: microaerotolerant or aerotolerant anaerobes can survive
  notes: Supports microaerotolerance as survival under limited oxygen exposure.
- reference: PMID:30113300
  snippet: The novel strain stains Gram-negative and Congo-red-negative and is characterized
    mesophilic, neutrophilic, chemoheterotrophic and microaerotolerant
  notes: 'Organism example: Simulacricoccus ruber strain MCy10636 is described as
    microaerotolerant.'
causal_graphs:
- graph_id: microaerotolerant_low_oxygen_defense
  title: Microaerotolerant low-oxygen survival mechanism
  description: Evidence-backed causal sketch linking microaerotolerance to limited
    oxygen exposure and oxidative stress defenses.
  nodes:
  - node_id: microaerotolerant_trait
    label: microaerotolerant
    node_type: TRAIT
    grounding: METPO:1000610
    description: Tolerates low oxygen without requiring it.
  - node_id: limited_oxygen_exposure
    label: limited oxygen exposure
    node_type: ENVIRONMENTAL_FACTOR
    description: Low-level oxygen exposure tolerated by microaerotolerant organisms.
  - node_id: reactive_oxygen_species
    label: reactive oxygen species
    node_type: CHEMICAL
    grounding: CHEBI:26523
    description: Oxygen-derived oxidants.
  - node_id: oxidative_stress_defense
    label: oxidative stress defense enzymes
    node_type: GENE_OR_PROTEIN
    description: Enzymes such as SOD, catalase, or peroxidase that mitigate ROS.
  - node_id: anaerobic_growth
    label: anaerobic growth
    node_type: BIOLOGICAL_PROCESS
    description: Growth that does not require oxygen.
  - node_id: intermediate_oxygen_level
    label: intermediate oxygen level
    node_type: ENVIRONMENTAL_FACTOR
    description: Sub-atmospheric, microoxic O2 concentration between anoxia and air.
  - node_id: superoxide
    label: superoxide
    node_type: CHEMICAL
    description: Superoxide radical anion, a reactive oxygen species.
    grounding: CHEBI:18421
  - node_id: superoxide_reductase
    label: superoxide reductase
    node_type: GENE_OR_PROTEIN
    description: Enzyme (SOR) that reduces superoxide to hydrogen peroxide.
    grounding: UniProtKB:A0A090JWT2
  - node_id: hydrogen_peroxide
    label: hydrogen peroxide
    node_type: CHEMICAL
    description: H2O2, a reactive oxygen species generated during O2 exposure.
    grounding: CHEBI:16240
  - node_id: rubrerythrin_peroxidase
    label: rubrerythrin/peroxidase
    node_type: GENE_OR_PROTEIN
    description: Rubrerythrin and peroxidase enzymes that reduce H2O2 to water.
  - node_id: reduced_electron_donors
    label: reduced electron donors (NADH)
    node_type: CHEMICAL
    description: Reduced electron donors such as NADH that power ROS-detoxifying enzymes.
  - node_id: gut_oxygen_gradient
    label: gut lumen oxygen gradient
    node_type: ENVIRONMENTAL_FACTOR
    description: Spatial O2 gradient in host gut, ~0.1-0.4% in lumen up to ~5% in
      tissues.
  - node_id: low_oxygen_defense_systems
    label: low-oxygen defense systems
    node_type: BIOLOGICAL_PROCESS
    description: Cellular systems mitigating ROS and consuming O2 under low-oxygen
      exposure.
  edges:
  - subject: limited_oxygen_exposure
    predicate: tolerated by
    object: microaerotolerant_trait
    description: Microaerotolerant organisms survive limited oxygen exposure.
    evidence:
    - reference: DOI:10.1016/j.biortech.2011.02.011
      snippet: microaerotolerant or aerotolerant anaerobes can survive
      notes: Supports low-oxygen survival as the defining trait context.
  - subject: microaerotolerant_trait
    predicate: does not require
    object: limited_oxygen_exposure
    description: Microaerotolerance differs from microaerophily because oxygen is
      tolerated rather than required.
    evidence:
    - reference: DOI:10.1038/nrmicro2970
      snippet: Many obligate anaerobes tolerate transient or low levels of O2
      notes: Supports low oxygen tolerance without implying oxygen requirement.
  - subject: limited_oxygen_exposure
    predicate: can generate
    object: reactive_oxygen_species
    description: Oxygen exposure can create ROS stress that tolerant organisms must
      manage.
    evidence:
    - reference: DOI:10.1038/s41579-021-00583-y
      snippet: molecular oxygen and ROS
      notes: Review links oxygen exposure with ROS stress.
  - subject: oxidative_stress_defense
    predicate: mitigates
    object: reactive_oxygen_species
    description: ROS detoxification enzymes contribute to oxygen tolerance.
    evidence:
    - reference: DOI:10.1128/iai.16.1.20-25.1977
      snippet: oxygen tolerance of anaerobes is usually related to their level of
        SOD
      notes: Supports antioxidant defense as a mechanism for oxygen tolerance.
    predicate_id: METPO:2007407
  - subject: microaerotolerant_trait
    predicate: compatible with
    object: anaerobic_growth
    description: Microaerotolerant organisms can remain anaerobic while surviving
      limited oxygen exposure.
    evidence:
    - reference: DOI:10.1016/j.biortech.2011.02.011
      snippet: microaerotolerant or aerotolerant anaerobes
      notes: Supports microaerotolerance as an anaerobe oxygen-tolerance subtype.
  - subject: intermediate_oxygen_level
    predicate: maximizes growth of
    object: microaerotolerant_trait
    description: Maximal growth of microaerotolerant cells often occurs at intermediate
      oxygen levels.
    evidence:
    - reference: DOI:10.1128/CMR.00110-14
      notes: Growth occurs in the presence or absence of oxygen; however, maximal
        growth occurs at intermediate oxygen levels.
  - subject: superoxide_reductase
    predicate: reduces
    object: superoxide
    description: Superoxide reductase reduces superoxide (to hydrogen peroxide) using
      reduced electron donors.
    evidence:
    - reference: DOI:10.1128/IAI.00502-24
      notes: Review notes SOR reduces superoxide using electrons from donors like
        NADH.
    predicate_id: METPO:2000017
  - subject: superoxide_reductase
    predicate: produces
    object: hydrogen_peroxide
    description: Reduction of superoxide by SOR yields hydrogen peroxide.
    evidence:
    - reference: DOI:10.1128/IAI.00502-24
      notes: SOR reduces superoxide to H2O2 as part of the anaerobe oxygen-defense
        backbone.
    predicate_id: METPO:2000202
  - subject: rubrerythrin_peroxidase
    predicate: reduces
    object: hydrogen_peroxide
    description: Rubrerythrin/peroxidases reduce hydrogen peroxide to water.
    evidence:
    - reference: DOI:10.1128/IAI.00502-24
      notes: Review states Rbr/peroxidases reduce H2O2 to water.
    predicate_id: METPO:2000017
  - subject: reduced_electron_donors
    predicate: enables function of
    object: oxidative_stress_defense
    description: Protection by SOR/Rbr defenses depends on available reduced electron
      donors.
    evidence:
    - reference: DOI:10.1128/IAI.00502-24
      notes: The protection conferred by SOR/Rbr depends on available reduced electron
        donors.
  - subject: gut_oxygen_gradient
    predicate: creates selection for
    object: low_oxygen_defense_systems
    description: Host gut oxygen gradients expose anaerobes to low O2, selecting for
      low-O2 defense systems.
    evidence:
    - reference: DOI:10.1128/IAI.00502-24
      notes: Gut O2 gradients (colon lumen 0.1-0.4% to ~5% in tissues) expose anaerobes
        to low O2 during colonization/inflammation.
curation_history:
- timestamp: '2026-05-05T01:35:46.854338+00:00'
  curator: seed_from_metpo
  action: SEEDED_FROM_METPO
  changes: imported from data/raw/metpo.owl (CLASS)
  llm_assisted: false
- timestamp: '2026-05-05T01:09:05-07:00'
  curator: codex
  action: CURATED_WITH_LITERATURE
  changes: Added source-backed evidence for microaerotolerant oxygen exposure survival.
  llm_assisted: true
- timestamp: '2026-05-05T18:39:46-07:00'
  curator: codex
  action: ADDED_ORGANISM_EXAMPLE
  changes: Added Simulacricoccus ruber organism example with PMID-backed evidence.
  llm_assisted: true
- timestamp: '2026-05-10T00:00:00-07:00'
  curator: codex
  action: ADDED_CAUSAL_GRAPH
  changes: Added DOI-backed causal graph for low-oxygen survival and oxidative stress
    defense in microaerotolerant organisms.
  llm_assisted: true
- timestamp: '2026-05-23T21:30:06Z'
  curator: claude
  action: GROUND_CAUSAL_PREDICATES
  changes: Grounded 1 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv
    (METPO:2007407×1).
  llm_assisted: true
- timestamp: '2026-06-17T04:09:43Z'
  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: '2026-06-24T17:21:10Z'
  curator: claude
  action: GROUND_CAUSAL_PREDICATES
  changes: Grounded 3 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv
    (METPO:2000017×2, METPO:2000202×1).
  llm_assisted: true
- timestamp: '2026-06-24T17:23:30Z'
  curator: claude
  action: GROUND_CAUSAL_NODES
  changes: Grounded 2 causal-node grounding field(s) via mappings/node_grounding.tsv
    (CHEBI:18421×1, CHEBI:16240×1).
  llm_assisted: true
- timestamp: '2026-06-26T07:15:17Z'
  curator: claude
  action: GROUND_CAUSAL_NODES
  changes: Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv
    (UniProtKB:A0A090JWT2×1).
  llm_assisted: true