identifier: traitmech:000043
label: parasitism
definition: A symbiosis in which the microorganism benefits at the expense of its
  host's fitness, deriving resources from the host while causing it harm.
definition_source: DOI:10.1038/s41579-021-00550-7
trait_category: ECOLOGY
term_kind: CLASS
mapping_status: REVIEWED
parent_traits:
- traitmech:000040
synonyms:
- synonym_text: parasitic
  synonym_type: RELATED_SYNONYM
  source: DOI:10.1038/s41579-021-00550-7
evidence:
- reference: DOI:10.1038/s41579-021-00550-7
  notes: Drew et al. define parasitism as the harmful pole of the parasite-mutualist
    continuum and describe evolutionary transitions along it.
- reference: DOI:10.1073/pnas.1218525110
  notes: McFall-Ngai et al. support host-exploitative associations as one outcome
    of the shared host-colonization toolkit.
canonical_examples:
- taxon_id: NCBITaxon:782
  taxon_label: Rickettsia prowazekii
  note: "Obligate intracellular parasite (epidemic typhus agent); textbook host-dependent intracellular lifestyle."
  reference: PMID:9823893
causal_graphs:
- graph_id: parasitism_host_fitness_cost
  title: Parasitism extracts resources at the host's expense
  description: Evidence-backed causal sketch linking host-resource exploitation to
    reduced host fitness in chronic parasitic association.
  nodes:
  - node_id: parasitism_trait
    label: parasitism
    node_type: TRAIT
    grounding: traitmech:000043
    description: Symbiosis with positive microbe fitness and negative host fitness.
  - node_id: host_resource_exploitation
    label: host resource exploitation
    node_type: BIOLOGICAL_PROCESS
    description: Acquisition of nutrients or shelter from the host at fitness cost.
  - node_id: host_fitness_cost
    label: host fitness cost
    node_type: QUALITY
    description: Net negative fitness change for the host partner.
  - node_id: bacterial_adhesin_activity
    label: bacterial adhesin activity
    node_type: MOLECULAR_FUNCTION
    description: Surface adhesin-mediated adherence to host tissues.
  - node_id: host_colonization
    label: host colonization
    node_type: BIOLOGICAL_PROCESS
    description: Establishment and persistence of the microbe on/in host tissue.
  - node_id: siderophore_secretion
    label: siderophore secretion
    node_type: BIOLOGICAL_PROCESS
    description: Secretion of metal-chelating siderophores that compete with host
      proteins.
  - node_id: host_metal_acquisition
    label: host metal acquisition
    node_type: BIOLOGICAL_PROCESS
    description: Acquisition of host-sequestered metals (e.g. iron) by the microbe.
  - node_id: deubiquitinase_activity
    label: pathogen deubiquitinase activity
    node_type: MOLECULAR_FUNCTION
    description: Pathogen-derived deubiquitinating enzyme activity acting on host
      ubiquitin signaling.
  - node_id: host_ubiquitin_pathway_exploitation
    label: host ubiquitin pathway exploitation
    node_type: BIOLOGICAL_PROCESS
    description: Manipulation of ubiquitin-dependent host processes during infection.
  - node_id: high_symbiont_density
    label: high symbiont density in host tissues
    node_type: QUALITY
    description: Elevated density of the symbiont within host tissues.
  - node_id: copper_stress
    label: copper stress
    node_type: ENVIRONMENTAL_FACTOR
    description: Environmental copper stress experienced by the host-symbiont system.
  - node_id: hemoglobin_uptake
    label: hemoglobin/heme uptake
    node_type: BIOLOGICAL_PROCESS
    description: Hemoglobin- and heme-uptake mechanisms used to acquire host nutrients.
  edges:
  - subject: host_resource_exploitation
    predicate: causes
    object: host_fitness_cost
    description: Sustained resource extraction reduces host fitness.
    evidence:
    - reference: DOI:10.1038/s41579-021-00550-7
      notes: Drew et al. define parasitism as the harmful pole of the parasite-mutualist
        continuum.
    predicate_id: biolink:causes
  - subject: host_fitness_cost
    predicate: enables
    object: parasitism_trait
    description: Chronic host fitness cost realizes the parasitic lifestyle.
    evidence:
    - reference: DOI:10.1073/pnas.1218525110
      notes: McFall-Ngai et al. support host-exploitative associations as one outcome
        of the shared host-colonization toolkit.
    predicate_id: RO:0002327
  - subject: bacterial_adhesin_activity
    predicate: promotes
    object: host_colonization
    description: Adhesin expression mediates adherence to host tissues, enabling colonization.
    evidence:
    - reference: DOI:10.1093/femsre/fuae019
      notes: 'Barber & Fitzgerald 2024: bacterial adhesins are critical for adherence
        to host tissues.'
    predicate_id: RO:0002213
  - subject: host_colonization
    predicate: enables
    object: host_resource_exploitation
    description: Established colonization provides access to host resources for exploitation.
    evidence:
    - reference: DOI:10.1093/femsre/fuae019
      notes: 'Barber & Fitzgerald 2024: host colonization is the basis for downstream
        host exploitation.'
    predicate_id: RO:0002327
  - subject: siderophore_secretion
    predicate: promotes
    object: host_metal_acquisition
    description: Secreted siderophores compete with host proteins for metals and are
      reacquired.
    evidence:
    - reference: DOI:10.1093/femsre/fuae019
      notes: 'Barber & Fitzgerald 2024: siderophores compete with host proteins for
        metals; metal-bound siderophores reacquired.'
    predicate_id: RO:0002213
  - subject: host_metal_acquisition
    predicate: part of
    object: host_resource_exploitation
    description: Metal scavenging is one mode of acquiring resources from the host.
    evidence:
    - reference: DOI:10.1093/femsre/fuae019
      notes: 'Barber & Fitzgerald 2024: nutrient/metal acquisition from host is a
        core exploitation mechanism.'
    predicate_id: biolink:part_of
  - subject: deubiquitinase_activity
    predicate: promotes
    object: host_ubiquitin_pathway_exploitation
    description: Pathogen DUBs exploit and manipulate ubiquitin-dependent host processes
      during infection.
    evidence:
    - reference: DOI:10.3389/fimmu.2023.1303072
      notes: 'Wehrmann & Vilchez 2023: DUBs are key factors exploiting/manipulating
        Ub-dependent host processes during infection.'
    predicate_id: RO:0002213
  - subject: host_ubiquitin_pathway_exploitation
    predicate: promotes
    object: host_resource_exploitation
    description: Manipulating host ubiquitin signaling supports microbe persistence
      and resource extraction.
    evidence:
    - reference: DOI:10.3389/fimmu.2023.1303072
      notes: 'Wehrmann & Vilchez 2023: manipulation of host Ub pathways supports infection
        establishment.'
    predicate_id: RO:0002213
  - subject: hemoglobin_uptake
    predicate: part of
    object: host_resource_exploitation
    description: Hemoglobin/heme uptake supplies nutrients enabling parasite survival
      in the host.
    evidence:
    - reference: DOI:10.3389/fcimb.2023.1150054
      notes: 'Reyes-Lopez et al. 2023: Hb and heme-uptake mechanisms allow protozoa
        to survive inside the host.'
    predicate_id: biolink:part_of
  - subject: high_symbiont_density
    predicate: causes
    object: host_fitness_cost
    description: High symbiont densities in host tissues drive strong negative host
      effects, even death.
    evidence:
    - reference: DOI:10.1002/ece3.11705
      notes: 'Hoffmann & Cooper 2024: high endosymbiont densities have particularly
        strong negative effects that can kill hosts.'
    predicate_id: biolink:causes
  - subject: copper_stress
    predicate: exacerbates
    object: host_fitness_cost
    description: Environmental copper stress exacerbates the pathogenic effects of
      parasitic symbionts on hosts.
    evidence:
    - reference: DOI:10.1093/ismejo/wrae100
      notes: 'Shi et al. 2024: pathogenic effects of parasitic symbionts on hosts
        were exacerbated under copper stress.'
curation_history:
- timestamp: '2026-06-02T00:00:00Z'
  curator: claude
  action: PROPOSED_FROM_RESEARCH
  changes: Proposed candidate ECOLOGY trait (parasitism); sub-variant of symbiosis.
    Distinct from pathogenic_to_host (acute disease causation).
  llm_assisted: true
- timestamp: '2026-06-09T14:00:00Z'
  curator: claude
  action: CURATED_CAUSAL_GRAPH
  changes: Added evidence-backed causal graph (parasitism / host fitness cost) with
    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 9 evidence-backed generic edges (9 new nodes) from the deep-research
    report.
  llm_assisted: true
- timestamp: '2026-06-24T17:21:09Z'
  curator: claude
  action: GROUND_CAUSAL_PREDICATES
  changes: Grounded 8 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv
    (RO:0002213×4, biolink:part_of×2, RO:0002327×1, biolink:causes×1).
  llm_assisted: true