identifier: traitmech:000208 label: homeoviscous adaptation definition: A stress response in which an organism remodels membrane lipid composition to maintain a functional membrane viscosity and fluidity when temperature changes perturb lipid packing. definition_source: DOI:10.1039/d4cc03114h trait_category: PHYSIOLOGY term_kind: CLASS mapping_status: PROPOSED parent_traits: - traitmech:000078 synonyms: - synonym_text: homoviscous adaptation synonym_type: EXACT_SYNONYM source: DOI:10.1146/annurev-micro-091313-103612 - synonym_text: HVA synonym_type: RELATED_SYNONYM source: DOI:10.1039/d4cc03114h evidence: - reference: DOI:10.1146/annurev-micro-091313-103612 snippet: termed homeoviscous adaptation notes: de Mendoza reviews the temperature-driven bacterial membrane remodeling response and names it homeoviscous adaptation. - reference: DOI:10.1128/spectrum.03925-23 snippet: Upon temperature decrease, the membrane rigidifies and increases in thickness, resulting in activation of the kinase-dominant state of DesK notes: Sidarta et al. support membrane rigidification and thickening as proximal physical triggers in the Bacillus subtilis DesK/DesR homeoviscous-adaptation model. - reference: DOI:10.1038/s41467-024-53677-5 snippet: hard-wired parameters calibrate the system to generate membrane compositions that maintain constant fluidity notes: Hoogerland et al. directly support E. coli temperature adaptation through a fatty-acid synthesis control system that maintains membrane fluidity. - reference: DOI:10.1038/s41467-024-53677-5 snippet: restores optimal membrane fluidity within a single generation notes: Hoogerland et al. directly connect the E. coli fatty-acid branchpoint valve and transcriptional feedback to rapid membrane-fluidity restoration after temperature shock. canonical_examples: - taxon_id: NCBITaxon:562 taxon_label: Escherichia coli note: E. coli rapidly restores membrane fluidity after temperature shock through a FabI/FabB branchpoint valve coupled to transcriptional feedback. reference: DOI:10.1038/s41467-024-53677-5 - taxon_id: NCBITaxon:1423 taxon_label: Bacillus subtilis note: B. subtilis is the model organism for DesK/DesR membrane thickness sensing and Des-mediated fatty-acyl-chain desaturation during cold-induced homeoviscous adaptation. reference: DOI:10.1128/spectrum.03925-23 causal_graphs: - graph_id: homeoviscous_adaptation_membrane_fluidity title: Membrane-fluidity homeostasis by lipid remodeling description: Evidence-backed causal sketch linking temperature-driven membrane rigidification to homeoviscous lipid remodeling and restored membrane fluidity. scope_status: MECHANISTIC scope_notes: This graph captures the conserved membrane-fluidity output of homeoviscous adaptation without making the Bacillus DesK/DesR two-component branch, E. coli FabI/FabB metabolic valve, or any single lipid species universal across microbes. nodes: - node_id: homeoviscous_adaptation_trait label: homeoviscous adaptation node_type: TRAIT grounding: traitmech:000208 description: Capacity to remodel membrane lipid composition to preserve functional membrane viscosity and fluidity. - node_id: temperature_downshift label: temperature downshift node_type: ENVIRONMENTAL_FACTOR description: A decrease in ambient temperature that orders the lipid bilayer. - node_id: membrane_rigidity label: membrane rigidification node_type: QUALITY description: Reduced membrane fluidity and increased bilayer thickness after cooling. - node_id: homeoviscous_adaptation_process label: homeoviscous adaptation node_type: BIOLOGICAL_PROCESS grounding: METPO:1016200 description: Temperature-responsive lipid remodeling that restores the membrane to a fluidity setpoint. - node_id: fab_fatty_acid_branchpoint_enzymes grounding_status: REVIEWED_LABEL_ONLY grounding_notes: Reviewed E. coli branchpoint protein set; no single taxon-agnostic family, activity, or complex term captures the FabI enoyl-ACP reductase and FabB beta-ketoacyl-ACP synthase pair without also adding unrelated fatty-acid synthesis components. label: FabI/FabB branchpoint enzymes node_type: GENE_OR_PROTEIN description: E. coli fatty-acid synthesis enzymes at the saturated/unsaturated branchpoint that route acyl-ACP flux during temperature adaptation. protein_examples: - uniprot_id: UniProtKB:P0AEK4 protein_label: Enoyl-[acyl-carrier-protein] reductase [NADH] FabI gene_symbol: fabI taxon_id: NCBITaxon:83333 taxon_label: Escherichia coli K-12 entry_status: REVIEWED retrieved_on: '2026-09-15' entry_version: 161 sequence_version: 2 role: E. coli K-12 FabI catalyzes enoyl-ACP reduction in fatty-acid elongation and participates in the FabI/FabB metabolic valve that allocates flux between saturated and unsaturated fatty-acid synthesis during homeoviscous adaptation. evidence: - reference: https://rest.uniprot.org/uniprotkb/P0AEK4.json snippet: Involved in the elongation cycle of fatty acid which are used in the lipid metabolism notes: Verified FabI identity and fatty-acid elongation role against the live UniProt REST entry for P0AEK4 retrieved on 2026-09-15. - reference: DOI:10.1038/s41467-024-53677-5 snippet: via the branchpoint enzymes FabI and FabB notes: Hoogerland et al. place FabI in the temperature-sensitive E. coli fatty-acid branchpoint valve. - uniprot_id: UniProtKB:P0A953 protein_label: 3-oxoacyl-[acyl-carrier-protein] synthase 1 gene_symbol: fabB taxon_id: NCBITaxon:83333 taxon_label: Escherichia coli K-12 entry_status: REVIEWED retrieved_on: '2026-09-15' entry_version: 155 sequence_version: 1 role: E. coli K-12 FabB elongates acyl-ACP substrates in fatty-acid biosynthesis and participates in the FabI/FabB metabolic valve that allocates flux between saturated and unsaturated fatty-acid synthesis during homeoviscous adaptation. evidence: - reference: https://rest.uniprot.org/uniprotkb/P0A953.json snippet: Catalyzes a key reaction in unsaturated fatty acid (UFA) synthesis notes: Verified FabB identity and unsaturated fatty-acid synthesis role against the live UniProt REST entry for P0A953 retrieved on 2026-09-15. - reference: DOI:10.1038/s41467-024-53677-5 snippet: via the branchpoint enzymes FabI and FabB notes: Hoogerland et al. place FabB in the temperature-sensitive E. coli fatty-acid branchpoint valve. - node_id: membrane_lipid_remodeling label: membrane lipid remodeling node_type: BIOLOGICAL_PROCESS description: Changes in membrane lipid unsaturation, branching, or chain length that alter lipid packing. - node_id: membrane_fluidity label: membrane fluidity node_type: QUALITY grounding: METPO:1007505 description: Dynamic lipid-bilayer state maintained near a functional setpoint by homeoviscous remodeling. edges: - subject: temperature_downshift predicate: causes object: membrane_rigidity description: A temperature decrease causes the bacterial membrane to rigidify and thicken. evidence: - reference: DOI:10.1128/spectrum.03925-23 snippet: Upon temperature decrease, the membrane rigidifies and increases in thickness notes: Sidarta et al. describe rigidification and thickening as the immediate membrane response to temperature decrease. predicate_id: biolink:causes - subject: membrane_rigidity predicate: positively regulates object: homeoviscous_adaptation_process description: Membrane rigidification is sensed as the physical input that activates homeoviscous lipid remodeling. evidence: - reference: DOI:10.1128/spectrum.03925-23 snippet: Upon temperature decrease, the membrane rigidifies and increases in thickness, resulting in activation of the kinase-dominant state of DesK notes: Sidarta et al. support the physical membrane-state trigger through the B. subtilis DesK sensor model. predicate_id: RO:0002213 - subject: homeoviscous_adaptation_process predicate: positively regulates object: membrane_lipid_remodeling description: Homeoviscous adaptation increases lipid remodeling routes, including fatty-acyl desaturation, that counteract bilayer ordering. evidence: - reference: DOI:10.1128/spectrum.03925-23 snippet: desaturates the fatty acyl chains, resulting in membrane fluidization and concomitant decrease of bilayer thickness notes: Sidarta et al. support Des-mediated fatty-acyl desaturation as a concrete B. subtilis homeoviscous remodeling branch. predicate_id: RO:0002213 - subject: fab_fatty_acid_branchpoint_enzymes predicate: regulates object: membrane_lipid_remodeling description: The E. coli FabI/FabB branchpoint valve allocates fatty-acid synthesis flux between saturated and unsaturated membrane-lipid routes. evidence: - reference: DOI:10.1038/s41467-024-53677-5 snippet: A first element of this regulatory system is a temperature-sensitive metabolic valve that allocates flux between the saturated and unsaturated fatty acid synthesis pathways via the branchpoint enzymes FabI and FabB notes: Hoogerland et al. support the E. coli FabI/FabB branchpoint valve as a regulator of flux between saturated and unsaturated fatty-acid synthesis. predicate_id: RO:0002211 - subject: membrane_lipid_remodeling predicate: regulates object: membrane_fluidity description: Temperature-dependent membrane lipid remodeling maintains membrane fluidity near a functional setpoint. evidence: - reference: DOI:10.1038/s41467-024-53677-5 snippet: hard-wired parameters calibrate the system to generate membrane compositions that maintain constant fluidity notes: Hoogerland et al. show that the E. coli fatty-acid synthesis system generates temperature-specific membrane compositions that maintain fluidity. predicate_id: RO:0002211 - subject: membrane_fluidity predicate: contributes to object: homeoviscous_adaptation_trait description: Restoration of optimal membrane fluidity is the physiological output of homeoviscous adaptation. evidence: - reference: DOI:10.1038/s41467-024-53677-5 snippet: restores optimal membrane fluidity within a single generation notes: Hoogerland et al. directly connect the homeoviscous fatty-acid control system to rapid fluidity restoration. predicate_id: RO:0002326 discussions: - discussion_id: homeoviscous-adaptation-xref-gap prompt: Resolve an exact external ontology class for organism-level homeoviscous adaptation before adding a TraitRecord xref. kind: CURATION_TODO status: OPEN rationale: No exact GO, PATO, or METPO class is present in the pinned local snapshot for homeoviscous adaptation. Related lipid metabolism, fatty-acid desaturation, membrane-fluidity, and cold-response terms are narrower, broader, or shifted from the whole-organism membrane-acclimation trait. posed_by: codex posed_date: '2026-09-15' curation_history: - timestamp: '2026-09-15T07:02:39Z' curator: codex action: MINTED_TRAITMECH_ID changes: Minted homeoviscous adaptation as a DOI-backed stress-response TraitRecord after a repository-wide duplicate review covering ignored and hidden files; the local METPO snapshot has no exact homeoviscous-adaptation class and the replacement placeholder is reserved in proposals/metpo_traitmech_v85. llm_assisted: true - timestamp: '2026-09-15T07:13:33Z' curator: codex action: ADD_PROTEIN_EXAMPLES changes: Added E. coli K-12 FabI and FabB UniProt protein examples to the homeoviscous adaptation causal graph and removed a top-level evidence item whose Maiti review citation had no verbatim snippet. llm_assisted: true - timestamp: '2026-09-15T07:26:31Z' curator: codex action: NORMALIZED_CAUSAL_NODE_ID changes: Renamed the homeoviscous graph node membrane_rigidification to the canonical membrane_rigidity QUALITY node id after PR review found that the retired process-shaped alias had been reintroduced. llm_assisted: true