identifier: METPO:1003008 label: acidotolerant definition: A pH growth preference characterized by the ability to tolerate acidic environments (typically pH below 5.5) while maintaining optimal growth near neutral pH. definition_source: DOI:10.1038/nrmicro2549 trait_category: ENVIRONMENT term_kind: CLASS mapping_status: REVIEWED parent_traits: - METPO:1003000 synonyms: - synonym_text: aciduric synonym_type: EXACT_SYNONYM source: metpo.owl created_by: Jed Dongjin Kim-Ozaeta evidence: - reference: DOI:10.1038/nrmicro2549 snippet: tolerate and grow at external pH values notes: Supports acidotolerance as growth or survival under otherwise stressful external pH conditions. canonical_examples: - taxon_id: NCBITaxon:1579 taxon_label: Lactobacillus acidophilus note: "tolerates/produces acid" reference: PMID:15345415 - taxon_id: NCBITaxon:435 taxon_label: Acetobacter aceti note: "acetic-acid tolerant" reference: PMID:17920150 causal_graphs: - graph_id: acidotolerant_acid_stress_homeostasis title: Acidotolerant acid-stress pH homeostasis mechanism description: Evidence-backed causal sketch linking acidotolerance to acidic exposure and maintenance of cytoplasmic pH near compatibility with growth. nodes: - node_id: acidotolerant_trait label: acidotolerant node_type: TRAIT grounding: METPO:1003008 description: Tolerates acidic conditions despite neutral-pH growth optimum. - node_id: acidic_exposure label: acidic exposure node_type: ENVIRONMENTAL_FACTOR description: External acidic pH stress. - node_id: proton label: proton node_type: CHEMICAL grounding: CHEBI:15378 description: Hydrogen ion contributing to acid stress. - node_id: cytoplasmic_ph_homeostasis label: cytoplasmic pH homeostasis node_type: BIOLOGICAL_PROCESS description: Cellular control of internal pH during acid stress. grounding: GO:0051453 - node_id: proton_efflux_transport label: proton efflux transport node_type: MOLECULAR_FUNCTION description: Export or exclusion of excess protons from the cytoplasm. - node_id: amino_acid_decarboxylation label: amino-acid decarboxylase system node_type: PATHWAY description: Proton-consuming amino-acid decarboxylation (e.g. glutamate/Gad system) that consumes intracellular H+. - node_id: membrane_lipid_remodeling label: membrane lipid remodeling node_type: BIOLOGICAL_PROCESS description: Changes in membrane lipid composition (e.g. cyclopropane fatty acid formation, altered saturated/unsaturated ratio) increasing acid resistance. - node_id: inward_proton_leakage label: inward proton leakage node_type: BIOLOGICAL_PROCESS description: Passive entry of protons across the membrane that challenges cytoplasmic pH homeostasis. - node_id: cation_proton_antiport label: cation/H+ antiport node_type: MOLECULAR_FUNCTION description: Na+/H+ and K+/H+ antiporter activity exchanging cations for protons to stabilize intracellular pH. edges: - subject: acidic_exposure predicate: challenges object: acidotolerant_trait description: Acidotolerant organisms withstand acidic external pH that can be toxic to non-adapted cells. evidence: - reference: DOI:10.1038/nrmicro2549 snippet: external pH values that would otherwise be toxic notes: Review supports pH tolerance as adaptation to toxic external pH. predicate_id: METPO:2007406 - subject: acidic_exposure predicate: increases influx pressure of object: proton description: Acid exposure increases proton pressure on the cytoplasmic membrane. evidence: - reference: DOI:10.1016/j.tim.2007.02.005 snippet: rate at which protons leak inward notes: Acidophile review frames proton leak as a pH-homeostasis challenge. - subject: proton_efflux_transport predicate: removes object: proton description: Proton export helps prevent excessive cytoplasmic acidification. evidence: - reference: DOI:10.1016/j.tim.2007.02.005 snippet: remove excess protons from the cytoplasm notes: Supports active proton removal as an acid-stress mechanism. - subject: cytoplasmic_ph_homeostasis predicate: enables object: acidotolerant_trait description: Acid tolerance depends on maintaining cytoplasmic pH during acid challenge. evidence: - reference: DOI:10.1038/nrmicro2549 snippet: bacterial pH homeostasis is a cell-wide physiological process notes: Supports pH homeostasis as a broad mechanism for acid tolerance. predicate_id: RO:0002327 - subject: amino_acid_decarboxylation predicate: maintains object: cytoplasmic_ph_homeostasis description: Amino-acid decarboxylation (e.g. GadA/B converting glutamate to GABA + CO2) consumes intracellular H+ and sustains cytoplasmic pH homeostasis under acid stress. evidence: - reference: DOI:10.3390/microorganisms12091774 notes: GadA/B decarboxylate glutamate to GABA + CO2 while consuming intracellular H+; broadly reusable proton-consuming module across bacteria/LAB. - subject: membrane_lipid_remodeling predicate: increases object: acidotolerant_trait description: Membrane lipid remodeling (e.g. conversion of unsaturated to cyclopropane fatty acids) reduces proton permeability and improves acid resistance. evidence: - reference: DOI:10.3390/microorganisms12091774 notes: Membrane lipids enhance acid resistance by altering saturated/unsaturated ratios or converting unsaturated fatty acids to cyclopropane fatty acids; generic membrane mechanism. predicate_id: RO:0002213 - subject: membrane_lipid_remodeling predicate: reduces object: inward_proton_leakage description: Changes in membrane lipids and porins minimize passive inward proton leakage, a broad cross-taxon pH-homeostasis mechanism. evidence: - reference: DOI:10.1038/nrmicro2549 notes: 'Krulwich review: changes in membrane lipids and porins minimize inward proton leakage.' predicate_id: METPO:2000017 - subject: inward_proton_leakage predicate: challenges object: cytoplasmic_ph_homeostasis description: Inward proton leakage raises cytoplasmic proton load, opposing maintenance of internal pH. evidence: - reference: DOI:10.1038/nrmicro2549 notes: pH homeostasis must counter inward proton leakage to keep cytoplasmic pH near neutral. predicate_id: METPO:2007406 - subject: cation_proton_antiport predicate: contributes to object: cytoplasmic_ph_homeostasis description: Na+/H+ and K+/H+ antiporters exchange cations for protons to stabilize intracellular pH, a core cross-bacterial homeostasis mechanism. evidence: - reference: DOI:10.1038/nrmicro2549 notes: Na+/H+ and K+/H+ antiporters support cytoplasmic pH control; generic across bacteria. predicate_id: RO:0002326 curation_history: - timestamp: '2026-05-05T01:35:46.941434+00:00' curator: seed_from_metpo action: SEEDED_FROM_METPO changes: imported from data/raw/metpo.owl (CLASS) llm_assisted: false - timestamp: '2026-05-11T00:00:00-07:00' curator: codex action: CURATED_WITH_LITERATURE changes: Reviewed acidotolerant trait and added DOI-backed evidence and causal graph for acid-stress pH homeostasis. llm_assisted: true - timestamp: '2026-05-20T03:35:29Z' 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:2007406×1). llm_assisted: true - timestamp: '2026-05-24T04:37:59Z' 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: '2026-06-15T07:20:36Z' 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 5 evidence-backed generic edges (4 new nodes) from the deep-research report. llm_assisted: true - timestamp: '2026-06-24T17:21:09Z' curator: claude action: GROUND_CAUSAL_PREDICATES changes: Grounded 4 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (RO:0002213×1, METPO:2000017×1, METPO:2007406×1, RO:0002326×1). llm_assisted: true