identifier: traitmech:000042 label: commensalism definition: A symbiosis in which the microorganism benefits from the association (e.g. resources, shelter, transport) while the host's fitness remains essentially unaffected. 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: commensal 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. place commensalism on the parasite-mutualist continuum as a near-neutral host interaction. - reference: DOI:10.1073/pnas.1218525110 notes: McFall-Ngai et al. support commensal colonization as a major class of host-associated microbial lifestyles. canonical_examples: - taxon_id: NCBITaxon:1282 taxon_label: Staphylococcus epidermidis note: "Archetypal human skin commensal." reference: PMID:33180890 causal_graphs: - graph_id: commensalism_neutral_host title: Commensalism benefits microbe without affecting host fitness description: Evidence-backed causal sketch linking host colonization to microbial benefit while host fitness is essentially neutral. nodes: - node_id: commensalism_trait label: commensalism node_type: TRAIT grounding: traitmech:000042 description: Microbe benefits from association; host fitness essentially neutral. - node_id: host_colonization label: host colonization node_type: BIOLOGICAL_PROCESS description: Persistent establishment of microbes on or in a host. - node_id: neutral_host_fitness label: neutral host fitness effect node_type: QUALITY description: No detectable net fitness change for the host partner. - node_id: secretory_iga label: secretory IgA node_type: GENE_OR_PROTEIN description: Host mucosal antibody that can promote commensal colonization of the mucus layer. - node_id: mucus_layer label: host mucus / mucins node_type: ENVIRONMENTAL_FACTOR description: Host-derived mucin glycan layer providing niche and nutrients for mucin-foraging microbes. - node_id: glycan_binding_proteins label: bacterial glycan-binding proteins node_type: GENE_OR_PROTEIN description: Microbial adhesins mediating attachment to host mucin glycans. - node_id: mucin_attachment label: attachment to mucin node_type: BIOLOGICAL_PROCESS description: Microbial adhesion to the host mucin layer supporting persistent colonization. - node_id: eps_production label: extracellular glucan / EPS production node_type: BIOLOGICAL_PROCESS description: Synthesis of extracellular polysaccharides that build the biofilm matrix. - node_id: biofilm_matrix label: EPS biofilm matrix node_type: CELLULAR_LOCALIZATION description: Extracellular polymeric matrix protecting cells from shear forces and antimicrobials. - node_id: persistence_protection label: protection from shear and antimicrobials node_type: QUALITY description: Resistance to physical removal and antimicrobials supporting host-niche persistence. - node_id: low_virulence label: low virulence / no detectable host cost node_type: QUALITY description: Microbe benefits from the host without causing a detectable fitness cost. edges: - subject: host_colonization predicate: enables object: commensalism_trait description: Persistent colonization without harm or benefit to the host realizes the commensal lifestyle. evidence: - reference: DOI:10.1073/pnas.1218525110 notes: McFall-Ngai et al. support commensal colonization as a major class of host-associated microbial lifestyles. predicate_id: RO:0002327 - subject: commensalism_trait predicate: associated with object: neutral_host_fitness description: Commensal interactions sit on the near-neutral point of the parasite-mutualist continuum. evidence: - reference: DOI:10.1038/s41579-021-00550-7 notes: Drew et al. place commensalism on the parasite-mutualist continuum as a near-neutral host interaction. predicate_id: biolink:associated_with - subject: secretory_iga predicate: promotes object: host_colonization description: Secretory IgA can help commensal bacteria colonize the mucus layer. evidence: - reference: DOI:10.1126/science.adi3338 notes: IgA can act as a carrot as well as a stick, helping bacteria colonize the mucus layer. predicate_id: RO:0002213 - subject: mucus_layer predicate: provides resources for object: host_colonization description: Host mucin glycans provide niche and nutrients enabling commensal persistence. evidence: - reference: DOI:10.1126/science.adi3338 notes: Mucin glycan availability selectively feeds mucin-degrading taxa, providing a host-derived resource. - subject: glycan_binding_proteins predicate: enables object: mucin_attachment description: Bacterial glycan-binding proteins mediate attachment to host mucin. evidence: - reference: DOI:10.1126/science.adi3338 notes: Bacteria attach to mucin via glycan-binding proteins. predicate_id: RO:0002327 - subject: mucin_attachment predicate: enables object: host_colonization description: Attachment to the mucin layer supports persistent host colonization. evidence: - reference: DOI:10.1126/science.adi3338 notes: Attachment to mucin via glycan-binding proteins underlies persistent colonization of the mucus niche. predicate_id: RO:0002327 - subject: eps_production predicate: produces object: biofilm_matrix description: Synthesis of extracellular glucans builds the EPS biofilm matrix. evidence: - reference: DOI:10.3389/fcimb.2024.1357631 notes: Synthesis of extracellular glucans builds the EPS biofilm matrix. predicate_id: METPO:2000202 - subject: biofilm_matrix predicate: confers object: persistence_protection description: The EPS biofilm matrix protects cells from shear forces and antimicrobials. evidence: - reference: DOI:10.3389/fcimb.2024.1357631 notes: Protects cells from shear forces and confers resistance to antimicrobials. - subject: persistence_protection predicate: promotes object: host_colonization description: Protection from removal and antimicrobials supports persistence in the host niche. evidence: - reference: DOI:10.3389/fcimb.2024.1357631 notes: Biofilm-conferred resistance supports persistence in a host niche. predicate_id: RO:0002213 - subject: low_virulence predicate: operationalizes object: commensalism_trait description: Benefit to the microbe with no detectable host cost operationalizes commensalism. evidence: - reference: DOI:10.1038/s41579-021-00550-7 notes: Commensals benefit from the interaction with hosts but do not cause a detectable cost. curation_history: - timestamp: '2026-06-02T00:00:00Z' curator: claude action: PROPOSED_FROM_RESEARCH changes: Proposed candidate ECOLOGY trait (commensalism); sub-variant of symbiosis. llm_assisted: true - timestamp: '2026-06-09T14:00:00Z' curator: claude action: CURATED_CAUSAL_GRAPH changes: Added evidence-backed causal graph (commensalism / neutral host fitness) 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 8 evidence-backed generic edges (8 new nodes) from the deep-research report. llm_assisted: true - timestamp: '2026-06-24T17:21:09Z' curator: claude action: GROUND_CAUSAL_PREDICATES changes: Grounded 5 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (RO:0002213×2, RO:0002327×2, METPO:2000202×1). llm_assisted: true discussions: - discussion_id: kgscan-3606bdcc991b prompt: 'Knowledge gap for commensalism: MicroRNAs (miRNAs) are small, noncoding RNAs involved in posttranscriptional gene regulation in both animal and plant. miRNAs derived from edible plants, referred to as xenomiRs, are proposed to cross-kingdom barriers and to modulate mammalian gene expression.' kind: KNOWLEDGE_GAP status: OPEN rationale: 'Surfaced by the Europe PMC literature gap-signal scan (categories: controversy_conflict, explicit_gap, future_work, limitations_barriers, unclear_unknown). Curator review required: set attaches_to, refine the prompt, and weigh the cited evidence.' attaches_to: [] evidence: - reference: PMID:40945860 supports: NO_EVIDENCE evidence_source: abstract snippet: MicroRNAs (miRNAs) are small, noncoding RNAs involved in posttranscriptional gene regulation in both animal and plant. miRNAs derived from edible plants, referred to as xenomiRs, are proposed to cross-kingdom barriers and to modulate mammalian gene expression. explanation: Gap-signal sentence (limitations_barriers) from the cited abstract. - reference: PMID:40574831 supports: NO_EVIDENCE evidence_source: abstract snippet: Emerging evidence suggests the gut microbiota plays a role in immune regulation, yet its impact on ITP remains unclear. explanation: Gap-signal sentence (unclear_unknown) from the cited abstract. - reference: PMID:42197356 supports: NO_EVIDENCE evidence_source: abstract snippet: Examining the existing literature may identify knowledge gaps regarding precise mechanisms through which the development of GM influences the maturation of the immune system. explanation: Gap-signal sentence (explicit_gap) from the cited abstract. - reference: PMID:41808832 supports: NO_EVIDENCE evidence_source: abstract snippet: Given its promising anti-inflammatory properties, further research is warranted. explanation: Gap-signal sentence (future_work) from the cited abstract. posed_by: kg-microbe-kgscan