identifier: METPO:1000460 label: pH range low definition: A pH range phenotype in which the growth-supporting external pH range spans approximately 4–6, characteristic of acidophilic physiology. definition_source: DOI:10.1038/nrmicro2549 trait_category: ENVIRONMENT term_kind: CLASS mapping_status: REVIEWED parent_traits: - METPO:1000332 synonyms: - synonym_text: Acid Tolerant synonym_type: EXACT_SYNONYM source: metpo.owl - synonym_text: Acidophile synonym_type: EXACT_SYNONYM source: metpo.owl - synonym_text: Facultative acidophile synonym_type: EXACT_SYNONYM source: metpo.owl - synonym_text: Obligative acidophile synonym_type: EXACT_SYNONYM source: metpo.owl - synonym_text: pHR_4_to_6 synonym_type: RELATED_SYNONYM source: metpo.owl evidence: - reference: DOI:10.1038/nrmicro2549 snippet: cytoplasmic pH notes: pH-homeostasis review supports moderately acidic pH-homeostasis as the basis of growth in the pH 4–6 range. causal_graphs: - graph_id: ph_range_low_acidophile_range title: pH-range-low acidophile range description: DOI-backed graph linking moderately acidophile pH-homeostasis to a pH growth range of approximately 4–6. nodes: - node_id: ph_range_low_trait label: pH range low node_type: TRAIT grounding: METPO:1000460 description: pH growth-supporting range approximately 4–6. - node_id: ph_range label: pH range node_type: TRAIT grounding: METPO:1000332 description: Span of external pH values supporting growth. - node_id: acidophile_homeostasis label: acidophile pH homeostasis node_type: BIOLOGICAL_PROCESS description: Proton extrusion and envelope barriers maintaining cytoplasmic pH against a moderately acidic external pH. - node_id: proton_motive_force label: proton motive force node_type: BIOLOGICAL_PROCESS description: Transmembrane electrochemical proton gradient maintained by H+ extrusion. - node_id: atp_synthase_atp_formation label: ATP synthase-mediated ATP formation node_type: BIOLOGICAL_PROCESS description: Phosphorylation of ADP to ATP driven by the proton motive force. - node_id: cyclopropane_fatty_acids label: cyclopropane fatty acids node_type: CHEMICAL description: Cyclopropane-fatty-acyl phospholipids produced by Cfa synthase that modify the membrane. - node_id: membrane_proton_permeability label: membrane proton permeability node_type: QUALITY description: Permeability of the cell membrane to protons. - node_id: undissociated_weak_acids label: undissociated weak organic acids node_type: CHEMICAL description: Protonated, membrane-permeant form of weak organic acids prevalent at low external pH. - node_id: weak_acid_influx label: weak organic acid influx into cell node_type: BIOLOGICAL_PROCESS description: Diffusion of undissociated weak organic acids across the membrane at low external pH. - node_id: weak_acid_dissociation label: intracellular dissociation of weak organic acids node_type: BIOLOGICAL_PROCESS description: Dissociation of weak acids in the near-neutral cytoplasm, releasing protons. - node_id: internal_ph label: internal (cytoplasmic) pH node_type: QUALITY description: pH of the cytoplasm. - node_id: h_atpase label: H+-ATPase proton efflux pump node_type: GENE_OR_PROTEIN description: ATP-driven proton-exporting ATPase (e.g. P-type H+-ATPase). - node_id: cytoplasmic_protons label: cytoplasmic protons node_type: CHEMICAL description: Protons (hydrons) within the cytoplasm. edges: - subject: acidophile_homeostasis predicate: enables object: ph_range_low_trait description: Acidophile pH-homeostasis enables growth across pH 4–6. evidence: - reference: DOI:10.1038/nrmicro2549 snippet: cytoplasmic pH notes: Supports acidophile cytoplasmic pH homeostasis as the moderately-acidic growth-range mechanism. predicate_id: RO:0002327 - subject: ph_range_low_trait predicate: is a object: ph_range description: pH range low is a quantitative bin of the pH-range phenotype. evidence: - reference: DOI:10.1016/j.tim.2007.02.005 snippet: proton motive force notes: Supports the pH 4–6 range as a value within the pH-range distribution. predicate_id: rdfs:subClassOf - subject: proton_motive_force predicate: drives object: atp_synthase_atp_formation description: The proton motive force drives ATP synthase phosphorylation of ADP to ATP. evidence: - reference: DOI:10.1111/1758-2229.70019 notes: '"That proton potential then drives the phosphorylation of ADP and the formation of ATP by the ATP synthase"; general bioenergetic edge relevant to low-pH growth.' - subject: cyclopropane_fatty_acids predicate: decreases object: membrane_proton_permeability description: Cyclopropane fatty acid membrane modification decreases proton permeability. evidence: - reference: DOI:10.4014/jmb.2303.03009 notes: '"decreasing membrane proton permeability prevents the accumulation of intracellular protons" after conversion to cyclopropane fatty acids; generalizable membrane adaptation.' predicate_id: RO:0002212 - subject: undissociated_weak_acids predicate: undergoes object: weak_acid_influx description: At low external pH weak organic acids are undissociated and diffuse into the cell. evidence: - reference: DOI:10.1111/1758-2229.70019 notes: '"organic acids... occur in their undissociated form and can diffuse into the cell"; boundary condition distinguishing low-pH growth from weak-acid inhibition.' - subject: weak_acid_dissociation predicate: lowers object: internal_ph description: Intracellular dissociation of weak organic acids releases protons and lowers cytoplasmic pH. evidence: - reference: DOI:10.1111/1758-2229.70019 notes: '"the higher pH of the cytoplasm will lead to dissociation of the acid, thus releasing protons and lowering the internal pH"; strong causal edge.' - subject: h_atpase predicate: exports object: cytoplasmic_protons description: H+-ATPases actively export protons from the cytoplasm using ATP. evidence: - reference: DOI:10.3389/fmicb.2023.1149903 notes: Acidophile genomes encode "a P-type ATPase proton efflux pump"; active ATP-driven proton export underlies cytoplasmic pH homeostasis. predicate_id: METPO:2000209 - subject: h_atpase predicate: contributes to object: acidophile_homeostasis description: ATP-driven proton export by H+-ATPases contributes to acidophile pH homeostasis. evidence: - reference: DOI:10.3390/microorganisms12030625 notes: '"acid stress tolerance... facilitated by an active export of protons via the expenditure of ATP... carried out by H+-ATPases"; broad principle of homeostasis.' predicate_id: RO:0002326 curation_history: - timestamp: '2026-05-05T01:35:46.829744+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 definition and causal graph linking acidophile pH-homeostasis to the pH-range-low bin. llm_assisted: true - timestamp: '2026-05-20T03:35:30Z' curator: claude action: GROUND_CAUSAL_PREDICATES changes: Grounded 2 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (RO:0002327×1, rdfs:subClassOf×1). llm_assisted: true - timestamp: '2026-06-23T00:00:00Z' curator: claude action: ENRICH_CAUSAL_GRAPH changes: Added 6 evidence-backed generic edges (10 new nodes) from the deep-research report. llm_assisted: true - timestamp: '2026-06-24T17:21:10Z' curator: claude action: GROUND_CAUSAL_PREDICATES changes: Grounded 3 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (RO:0002212×1, METPO:2000209×1, RO:0002326×1). llm_assisted: true