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host-associated

traitmech:000049 · CLASS · REVIEWED

A habitat association in which an organism lives persistently on or in a plant or animal host (e.g. as a member of a host microbiome), spanning commensal, mutualistic, and pathogenic relationships.

Host association establishes persistent host microbiome membership

Evidence-backed causal sketch linking host habitat to persistent membership in a host-associated microbial community.

Host association establishes persistent host microbiome membership Interactive directed graph showing evidence-backed causal relationships for host-associated.

Edge evidence

  • host habitat enables host colonization RO:0002327

    Host tissues provide the habitat in which the microbe colonizes.

    • DOI:10.1073/pnas.1218525110 McFall-Ngai et al. document ubiquitous host-associated microbial communities across animals.
  • host colonization confers host-associated METPO:2007700

    Persistent host colonization realizes the host-associated lifestyle.

    • DOI:10.1126/science.1104816 Bäckhed et al. characterize host-associated microbiota as dense, coevolved communities.
  • mucin O-glycans serves as nutrient source for host colonization

    Mucin O-glycans are degraded and utilized as a nutrient source supporting colonization.

    • DOI:10.1152/ajpgi.00261.2022 Mucin O-glycans and glycan-derived sugars are degraded and utilized as a nutrient source by host-associated microbes.
  • cell appendages and adhesins enables attachment to host surfaces RO:0002327

    Cell appendages and adhesins mediate attachment to host mucus and epithelia.

    • DOI:10.1093/femsre/fuae008 Cell appendages (flagella, pili, fimbriae) and adhesins mediate attachment to host mucus/epithelia.
  • attachment to host surfaces enables host colonization RO:0002327

    Attachment to host surfaces is a prerequisite step for persistent colonization.

    • DOI:10.1093/femsre/fuae008 Attachment to host surfaces underlies the transition to stable colonization.
  • c-di-GMP and cAMP second messengers induces biofilm formation

    c-di-GMP and cAMP trigger EPS and surface-protein production, driving irreversible attachment and biofilm.

    • DOI:10.1093/femsre/fuae008 cAMP and c-di-GMP regulate transition from reversible to irreversible attachment, triggering surface proteins and EPS leading to biofilm formation.
  • biofilm formation enables host colonization RO:0002327

    Biofilm formation supports persistent microbial occupancy of host surfaces.

    • DOI:10.1093/femsre/fuae008 Biofilm formation following irreversible attachment supports persistent host colonization.
  • plant root exudates activates chemotaxis toward host RO:0002213

    Root exudates trigger chemotaxis via MCP/CheA/CheY signaling toward the host.

    • DOI:10.3390/biology13020095 Methyl-accepting chemotaxis proteins bind root exudates and trigger signal transduction (CheW/CheA/CheY), driving chemotaxis as the first colonization step.
  • chemotaxis toward host enables host colonization RO:0002327

    Chemotaxis toward host cues is an initial step enabling colonization.

    • DOI:10.3390/biology13020095 Chemotaxis is identified as the first step of host colonization.
  • plant root exudates provides nutrient source for host colonization

    Root exudates supply carbon and substrates supporting microbial growth and persistence.

    • DOI:10.1093/femsre/fuad066 Plants secrete 11-40% of photosynthate as exudates that supply carbon and substrates for rhizobacterial growth and persistence.
  • mucus layer niches enables host colonization RO:0002327

    Structured inner and outer mucus layers create distinct niches for microbial colonization.

    • DOI:10.1128/ecosalplus.esp-0006-2023 Structured inner (firm, sparsely colonized) versus outer (looser, microbe-colonized) mucus creates distinct colonization niches.

Provenance

Source
METPO (2025-11-25)
Definition source
DOI:10.1073/pnas.1218525110

Parent traits (1)

Children (1)

kg-microbe context

Matched 1 kg-microbe node via parent_proxy.

  • METPO:1000059 [-2.682, -2.070, -3.656, -0.652, …]

512-dim DeepWalkSkipGramEnsmallen embedding from kg-microbe (2026-04-25).

Nearest neighbors in embedding space

Top-8 cosine-similar METPO traits from the 2026-04-25 deepwalk (512-D).

Deep research

Generated by just research-trait; source: research/traits/ecology/host_associated-deep-research-falcon.md

Unreviewed literature output — not curated TraitMech content Ontology identifiers suggested below have not been resolved against their ontologies, and some are known to be wrong. Check any CURIE against the source before using it. 
# TraitMech curation report: **host-associated**

## Executive scope

**Target:** `traitmech:000049` — host-associated; ecology class; reviewed mapping.

The defensible operational phenotype is **persistent residence on or in a living plant or animal host**, including epithelial surfaces, mucus, gut lumen, rhizoplane, and internal host tissues. The interaction outcome is orthogonal: pathogenic, commensal, and mutualistic organisms can all be host-associated. Wiesmann and colleagues state that “regardless of the outcome of symbiosis… bacteria must first colonize their hosts” and identify host sensing, nutrient acquisition, competition, immune tolerance, and physiological remodeling as shared requirements (published 15 December 2022 online; 2023 issue). (wiesmann2023originsofsymbiosis pages 1-2)

The causal graph should therefore terminate in **persistent host colonization/host-associated lifestyle**, not in host benefit, disease, or virulence. Those are possible downstream outcomes. Modern expert synthesis further emphasizes that host association is bidirectional: host immunity, barriers, physiological homeostasis, and transit actively select microbial residents, making the microbiome an “ecosystem on a leash” rather than a community controlled only by microbial genes or diet. (wilde2024hostcontrolof pages 1-5)

### Boundary cases

Include:

- Stable gut, skin, oral, respiratory, reproductive, leaf, root-surface, nodule, or endophytic residence.
- Commensals, mutualists, pathobionts, and persistent pathogens.
- Rhizosphere organisms only when persistence in the root-influenced compartment is demonstrated; the current plant literature explicitly uses “rhizosphere colonization” for stable communities in rhizosphere soil, rhizoplane, or root endosphere. (liu2024rootcolonizationby pages 1-2)

Exclude or qualify:

- Transient contamination, brief passage through a gut, or detection based only on environmental DNA.
- Mere proximity to a host without evidence of persistence.
- Adhesion in vitro as a synonym for the complete trait; adhesion is one possible enabling mechanism.
- “Intracellular,” “pathogenic,” “mutualistic,” “commensal,” and “host-specific” as equivalents. Each is a narrower or independent trait.
- Genes associated with one host species as universal determinants of host association.

## Current mechanistic model

A useful graph architecture is:

**host-derived signals and environmental conditions → sensing/chemotaxis and physiological response → host approach → surface attachment → access to host nutrients + resistance to host defenses + competition with resident microbes → biofilm or niche persistence → persistent host association.**

This is not a single obligatory pathway. Nonmotile vertically transmitted symbionts, intracellular specialists, and organisms lacking classical biofilms can reach the same ecological phenotype through different mechanisms. Thus, most nodes below should be modeled as context-dependent contributors rather than necessary-and-sufficient universal causes.

## Candidate nodes grouped by type

### Trait and ecological-state nodes

- **host-associated** — `traitmech:000049`
- persistent host colonization — label-only candidate
- long-term host association — label-only candidate
- host-surface colonization — label-only candidate
- rhizosphere colonization — label-only; scope includes rhizosphere soil, rhizoplane, and endosphere in the cited review (liu2024rootcolonizationby pages 1-2)
- intestinal colonization — label-only candidate
- microbial competition within host niche — label-only candidate
- colonization resistance — label-only candidate

### Host environments and experimental factors

- animal host; plant host — broad label-only classes
- intestinal mucus / mucin — label-only unless a specific mucin is used
- intestinal epithelium; plant root; rhizoplane; root endosphere — label-only candidates
- rhizosphere — `ENVO:00005801`
- root exudates — label-only mixture; do not represent as one chemical
- host innate immune response — `GO:0045087`
- host antimicrobial peptide exposure — label-only environmental factor
- reactive oxygen species exposure — label-only; individual ROS can receive CHEBI identifiers
- reactive nitrogen species / nitric oxide exposure — nitric oxide `CHEBI:16480`
- oxygen availability — oxygen `CHEBI:15379`
- host transit or expulsion — label-only process

Showing the first 60 of 253 lines of findings; the linked file also carries the run's front matter and the prompt it was given — read the full report.

Curation history

  1. · PROPOSED_FROM_RESEARCH · claude

    Proposed candidate ECOLOGY trait (host-associated); sub-variant of habitat association, parent of gut-associated.

  2. · CURATED_CAUSAL_GRAPH · claude

    Added evidence-backed causal graph (host-associated microbiome membership) with RO predicate groundings; promoted PROPOSED to REVIEWED.

  3. · ENRICH_CAUSAL_GRAPH · claude

    Added 9 evidence-backed generic edges (8 new nodes) from the deep-research report.

  4. · GROUND_CAUSAL_PREDICATES · claude

    Grounded 6 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (RO:0002327×5, RO:0002213×1).

  5. · GROUND_CAUSAL_NODES · claude

    Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv (GO:0042710×1).

  6. · MIGRATE_ENABLES_TRAIT_EDGES · claude

    Migrated 1 causal edge(s) off enables/RO:0002327 with a TRAIT object (1 to confers), issue 302. RO:0002327 has range 'biological process or activity', which a trait (a disposition) cannot satisfy, so the previous form entailed trait is-a BiologicalProcessOrActivity. The replacements are proposed in proposals/metpo_traitmech_v8 and are placeholder ids until METPO mints them.

  7. · NORMALISE_NODE_SENSE · claude

    One node_id per SENSE (issues 356, 384): root_exudates is the chemical sense here. The substance, not the condition: root exudates are a set of compounds, which is what CHEMICAL is for. rhizosphere_association.yaml settles it by modelling both — root_exudates (CHEMICAL) -causes-> rhizosphere_habitat (ENVIRONMENTAL_FACTOR) — the same two-ids shape this tranche applies to oxygen.