identifier: METPO:1000331 label: pH optimum definition: A pH phenotype with numerical limits that represents the external pH conditions at which an organism exhibits the most efficient growth and reproduction. definition_source: DOI:10.1038/nrmicro2549 trait_category: ENVIRONMENT term_kind: CLASS mapping_status: REVIEWED parent_traits: - METPO:1000531 - METPO:1000536 evidence: - reference: DOI:10.1038/nrmicro2549 snippet: cytoplasmic pH notes: pH-homeostasis review supports the external pH at which cytoplasmic pH is best maintained as the operational definition of pH optimum. - reference: DOI:10.1016/j.tim.2007.02.005 snippet: proton motive force notes: pH-homeostasis review supports the balanced proton motive force at the optimal external pH as the mechanism enabling maximal growth. causal_graphs: - graph_id: ph_optimum_balanced_homeostasis title: pH-optimum balanced cytoplasmic homeostasis description: DOI-backed graph linking the external pH at which cytoplasmic pH-homeostasis machinery operates with minimal load to maximal growth and the pH-optimum phenotype. nodes: - node_id: ph_optimum_trait label: pH optimum node_type: TRAIT grounding: METPO:1000331 description: External pH at which growth rate is maximal. - node_id: external_ph label: external pH node_type: ENVIRONMENTAL_FACTOR description: Ambient proton activity (pH) imposed on the cell. - node_id: proton label: proton node_type: CHEMICAL grounding: CHEBI:15378 description: H+ ion whose transmembrane gradient drives the proton motive force. - node_id: cytoplasmic_ph_homeostasis label: cytoplasmic pH homeostasis node_type: BIOLOGICAL_PROCESS description: Maintenance of a near-neutral cytoplasmic pH against the external H+ gradient. grounding: GO:0051453 - node_id: proton_motive_force label: proton motive force node_type: STATE description: Electrochemical proton gradient powering ATP synthesis and transport. grounding: METPO:1007500 - node_id: maximal_growth_rate label: maximal growth rate node_type: BIOLOGICAL_PROCESS description: Peak specific growth rate achieved at the optimal external pH. - node_id: atp_synthesis label: ATP synthesis by F0F1-ATP synthase node_type: BIOLOGICAL_PROCESS description: Synthesis of ATP driven by proton flux through the F0F1-ATP synthase. - node_id: na_h_antiporter_activity label: Na+/H+ antiporter activity node_type: MOLECULAR_FUNCTION description: Proton-sensing antiporter that exports Na+/K+ in exchange for protons to acidify the cytoplasm. - node_id: cytoplasm_acidification label: cytoplasm acidification node_type: BIOLOGICAL_PROCESS description: Lowering of cytoplasmic pH when internal pH becomes too high. - node_id: decarboxylation_pathways label: metabolite decarboxylation pathways node_type: PATHWAY description: Proton-consuming decarboxylation reactions that contribute to pH homeostasis and energy conservation. - node_id: cytoplasmic_buffering_capacity label: cytoplasmic buffering capacity node_type: CAPACITY description: Capacity of cytoplasmic buffers (e.g. inorganic/organic phosphates) to absorb pH fluctuations. - node_id: internal_ph label: internal pH node_type: STATE description: Cytoplasmic proton activity (pH) maintained near neutrality. edges: - subject: external_ph predicate: imposes gradient of object: proton description: External pH imposes a transmembrane H+ gradient on the cell. evidence: - reference: DOI:10.1016/j.tim.2007.02.005 snippet: major contributor to the proton motive force notes: Supports the transmembrane H+ gradient as the determinant of the proton motive force. predicate_id: METPO:2007601 - subject: cytoplasmic_ph_homeostasis predicate: regulates object: proton_motive_force description: Cytoplasmic pH homeostasis maintains a balanced proton motive force at the optimal external pH. evidence: - reference: DOI:10.1038/nrmicro2549 snippet: pH homeostasis notes: Supports pH homeostasis as the mechanism balancing the proton motive force. predicate_id: RO:0002211 - subject: proton_motive_force predicate: enables object: maximal_growth_rate description: A balanced proton motive force enables peak growth. evidence: - reference: DOI:10.1016/j.tim.2007.02.005 snippet: proton motive force notes: Supports the proton motive force as the energetic basis of growth at the optimal external pH. predicate_id: RO:0002327 - subject: maximal_growth_rate predicate: manifests as object: ph_optimum_trait description: The external pH supporting peak growth manifests the pH-optimum phenotype. evidence: - reference: DOI:10.1038/nrmicro2549 snippet: cytoplasmic pH notes: Supports the trait endpoint. predicate_id: METPO:2007400 - subject: external_ph predicate: contributes to object: proton_motive_force description: The external pH largely determines the magnitude of the pH gradient (ΔpH) component of the proton motive force. evidence: - reference: DOI:10.1093/femsre/fuad033 notes: Cells maintain cytoplasmic pH near neutral, so the magnitude of the pH gradient is largely determined by the external pH. predicate_id: RO:0002326 - subject: proton_motive_force predicate: drives object: atp_synthesis description: The proton motive force drives ATP synthesis via the F0F1-ATP synthase. evidence: - reference: DOI:10.1093/femsre/fuad033 notes: PMF drives the synthesis of ATP; the F0F1-ATP synthase uses three to five protons to synthesize one ATP. - subject: na_h_antiporter_activity predicate: enables object: cytoplasm_acidification description: Proton-sensing Na+/H+ (and K+/H+) antiporters acidify the cytoplasm when internal pH gets too high. evidence: - reference: DOI:10.1093/femsre/fuad033 notes: Proton-sensing ion/H+ antiporters acidify the cytoplasm by exporting K+ or Na+ in exchange for protons when the internal pH gets too high. predicate_id: RO:0002327 - subject: cytoplasm_acidification predicate: regulates object: cytoplasmic_ph_homeostasis description: Antiporter-driven cytoplasm acidification contributes to cytoplasmic pH homeostasis. evidence: - reference: DOI:10.1093/femsre/fuad033 notes: Acidifying the cytoplasm when internal pH gets too high is a homeostatic mechanism maintaining near-neutral cytoplasmic pH. predicate_id: RO:0002211 - subject: decarboxylation_pathways predicate: contributes to object: cytoplasmic_ph_homeostasis description: Proton-consuming decarboxylation reactions raise the internal pH and contribute to pH homeostasis. evidence: - reference: DOI:10.1093/femsre/fuad033 notes: The chemistry of the decarboxylation reaction requires a proton, raising internal pH, and the enzymes have a built-in self-regulatory mechanism contributing to pH homeostasis. predicate_id: RO:0002326 - subject: decarboxylation_pathways predicate: generates object: proton_motive_force description: Free energy from decarboxylation reactions can be stored as a proton motive force. evidence: - reference: DOI:10.1093/femsre/fuad033 notes: The free energy change from decarboxylation reactions can be stored in the form of a proton motive force. predicate_id: biolink:produces - subject: cytoplasmic_buffering_capacity predicate: regulates object: internal_ph description: Cytoplasmic buffering capacity stabilizes the internal pH by absorbing pH fluctuations. evidence: - reference: DOI:10.1093/femsre/fuad033 notes: The buffering capacity of the cytoplasm is important in absorbing pH fluctuations (e.g. inorganic and organic phosphates). predicate_id: RO:0002211 curation_history: - timestamp: '2026-05-05T01:35:46.814691+00:00' curator: seed_from_metpo action: SEEDED_FROM_METPO changes: imported from data/raw/metpo.owl (CLASS) llm_assisted: false - timestamp: '2026-05-13T10:00:00-07:00' curator: claude action: CURATED_CAUSAL_GRAPH changes: Added DOI-backed causal graph linking external pH, cytoplasmic pH homeostasis, the proton motive force, and maximal growth to the pH-optimum phenotype. llm_assisted: true - timestamp: '2026-05-20T03:35:30Z' curator: claude action: GROUND_CAUSAL_PREDICATES changes: Grounded 1 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (RO:0002327×1). 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:2007400×1). llm_assisted: true - timestamp: '2026-05-24T04:13:18Z' curator: claude action: RENAME_PREDICATE_LABELS changes: 'Renamed 1 causal-edge predicate label(s) to align with existing groundings: maintains → regulates ×1.' llm_assisted: true - timestamp: '2026-05-24T04:13:21Z' curator: claude action: GROUND_CAUSAL_PREDICATES changes: Grounded 1 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (RO:0002211×1). llm_assisted: true - timestamp: '2026-05-24T04:38:00Z' curator: claude action: GROUND_CAUSAL_NODES changes: Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv (GO:0030641×1). llm_assisted: true - timestamp: '2026-05-24T04:41:03Z' curator: claude action: GROUND_CAUSAL_NODES changes: Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv (METPO:1007500×1). llm_assisted: true - timestamp: '2026-05-26T02:30:12Z' curator: claude action: RETYPE_CAUSAL_NODES changes: 'Re-typed 1 causal-node node_type field(s) to align with CausalNodeTypeEnum semantics: proton motive force: BIOLOGICAL_PROCESS → STATE ×1.' llm_assisted: true - timestamp: '2026-06-14T07:26:19Z' curator: claude action: GROUND_CAUSAL_PREDICATES changes: Grounded 1 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (METPO:2007601×1). llm_assisted: true - timestamp: '2026-06-15T07:20:36Z' curator: claude action: FIX_NODE_GROUNDING_CURIE changes: Overwrote 1 causal-node grounding(s) (obsolete/wrong GO -> corrected, verified vs OAK). llm_assisted: true - timestamp: '2026-06-23T00:00:00Z' curator: claude action: ENRICH_CAUSAL_GRAPH changes: Added 7 evidence-backed generic edges (6 new nodes) from the deep-research report. llm_assisted: true - timestamp: '2026-06-24T17:21:10Z' curator: claude action: GROUND_CAUSAL_PREDICATES changes: Grounded 6 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (RO:0002326×2, RO:0002211×2, RO:0002327×1, biolink:produces×1). llm_assisted: true