identifier: METPO:1000468 label: NaCl optimum high definition: A NaCl optimum phenotype with the best-growth NaCl concentration above approximately 8% (w/v), corresponding to extreme-halophile physiology. definition_source: DOI:10.1093/femsre/fuy009 trait_category: ENVIRONMENT term_kind: CLASS mapping_status: REVIEWED parent_traits: - METPO:1000333 synonyms: - synonym_text: Extreme halophile synonym_type: EXACT_SYNONYM source: metpo.owl - synonym_text: NaO_>8 synonym_type: RELATED_SYNONYM source: metpo.owl evidence: - reference: DOI:10.1093/femsre/fuy009 snippet: extreme halophile notes: Osmoadaptation review supports >8% NaCl optimum as the extreme-halophile category. - reference: DOI:10.1186/1746-1448-4-2 snippet: KCl accumulating Halobacterium salinarum notes: Saline-Systems review supports the salt-in (intracellular KCl) strategy as the mechanism for extreme-halophile growth. causal_graphs: - graph_id: nacl_optimum_high_extreme_halophile title: NaCl-optimum-high extreme-halophile setpoint description: DOI-backed graph linking salt-in ion-accumulation strategy under hypersaline NaCl to a >8% (w/v) NaCl-optimum (extreme halophile). nodes: - node_id: nacl_optimum_high_trait label: NaCl optimum high node_type: TRAIT grounding: METPO:1000468 description: NaCl optimum exceeding ~8% w/v. - node_id: nacl_optimum label: NaCl optimum node_type: TRAIT grounding: METPO:1000333 description: NaCl concentration supporting maximal growth. - node_id: hypersaline_nacl label: hypersaline NaCl node_type: ENVIRONMENTAL_FACTOR description: External NaCl above ~8% w/v, typical of brines and salt lakes. - node_id: salt_in_strategy label: salt-in strategy node_type: BIOLOGICAL_PROCESS description: Intracellular K+ accumulation balancing high external NaCl osmotic activity. grounding: METPO:1007720 - node_id: intracellular_kcl label: intracellular KCl concentration node_type: CHEMICAL description: High cytoplasmic potassium chloride (>3 M) balancing external osmolarity in salt-in halophiles. - node_id: potassium_uptake_system label: potassium uptake system node_type: GENE_OR_PROTEIN description: K+ transporters/channels (Trk-family) mediating potassium accumulation for the salt-in strategy. - node_id: na_h_antiporter label: Na+/H+ antiporter node_type: GENE_OR_PROTEIN description: Sodium/proton antiporter mediating Na+ exclusion and ion homeostasis under high salt. grounding: UniProtKB:A0A068T423 - node_id: acidic_proteome label: acidic proteome node_type: QUALITY description: Proteome enriched in acidic residues (Asp/Glu) with low median pI, hallmark of salt-in halophiles. - node_id: protein_function_high_salinity label: protein function at high salinity node_type: MOLECULAR_FUNCTION description: Maintenance of protein structure and activity at molar intracellular salt concentrations. - node_id: acidic_aa_content label: increased acidic amino-acid content node_type: QUALITY description: Elevated Asp/Glu content in proteins promoting solubility in high intracellular KCl. - node_id: protein_solubility_high_salt label: protein solubility in high salt node_type: QUALITY description: Salt-induced stabilization and solubility of halophilic proteins at high salinity. edges: - subject: hypersaline_nacl predicate: selects for object: salt_in_strategy description: Hypersaline conditions select for intracellular ion-accumulation osmoadaptation. evidence: - reference: DOI:10.1186/1746-1448-4-2 snippet: KCl accumulating Halobacterium salinarum notes: Supports the salt-in strategy in extreme-halophile lineages. predicate_id: METPO:2007401 - subject: salt_in_strategy predicate: produces object: nacl_optimum_high_trait description: Salt-in ion accumulation yields a >8% NaCl-optimum setpoint. evidence: - reference: DOI:10.1093/femsre/fuy009 snippet: extreme halophile notes: Supports the >8% optimum as the extreme-halophile outcome. predicate_id: METPO:2000202 - subject: nacl_optimum_high_trait predicate: is a object: nacl_optimum description: NaCl optimum high is a quantitative bin of the NaCl-optimum phenotype. evidence: - reference: DOI:10.1093/femsre/fuy009 snippet: optimal NaCl notes: Supports >8% optimum as a value within the NaCl-optimum distribution. predicate_id: rdfs:subClassOf - subject: salt_in_strategy predicate: increases object: intracellular_kcl description: Salt-in osmoadaptation accumulates high intracellular KCl. evidence: - reference: DOI:10.1002/pro.5003 notes: Halophiles accumulate intracellular concentrations of potassium chloride even above 3 M. predicate_id: RO:0002213 - subject: salt_in_strategy predicate: requires object: potassium_uptake_system description: Salt-in strategy depends on K+ uptake systems to accumulate cytoplasmic potassium. evidence: - reference: DOI:10.1002/pro.5003 notes: Upregulating potassium-selective ion channels supports salt-in K+ accumulation. - subject: na_h_antiporter predicate: supports object: salt_in_strategy description: Na+/H+ antiporter activity supports salt-in osmoadaptation via Na+ exclusion. evidence: - reference: DOI:10.3390/microorganisms12081738 notes: Na+ extrusion via Na+/H+ antiporters driven by a proton electrochemical gradient. - subject: intracellular_kcl predicate: selects for object: acidic_proteome description: High intracellular KCl selects for an acidic proteome. evidence: - reference: DOI:10.1038/s41559-024-02505-6 notes: The salt-in strategy is concomitant with an excess of acidic amino acids. predicate_id: METPO:2007401 - subject: acidic_proteome predicate: enables object: protein_function_high_salinity description: Acidic proteome enables protein function at high salinity. evidence: - reference: DOI:10.1038/s41559-024-02505-6 notes: Proteome acidification preserves protein structure/function under high intracellular salt. predicate_id: RO:0002327 - subject: acidic_aa_content predicate: increases object: protein_solubility_high_salt description: Increased acidic amino-acid content increases protein solubility in high salt. evidence: - reference: DOI:10.1002/pro.5003 notes: Increase the number of short, polar and acidic amino acids to improve salt-induced stabilization and solubility. predicate_id: RO:0002213 curation_history: - timestamp: '2026-05-05T01:35:46.835295+00:00' curator: seed_from_metpo action: SEEDED_FROM_METPO changes: imported from data/raw/metpo.owl (CLASS) llm_assisted: false - timestamp: '2026-05-12T10:00:00-07:00' curator: claude action: CURATED_CAUSAL_GRAPH changes: Added DOI-backed definition and causal graph linking salt-in ion-accumulation strategy under hypersaline NaCl to the extreme-halophile NaCl-optimum 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 (METPO:2000202×1, rdfs:subClassOf×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:2007401×1). llm_assisted: true - timestamp: '2026-06-16T06:54:39Z' curator: claude action: GROUND_CAUSAL_NODES changes: Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv (METPO:1007720×1). llm_assisted: true - timestamp: '2026-06-23T00:00:00Z' curator: claude action: ENRICH_CAUSAL_GRAPH changes: Added 6 evidence-backed generic edges (7 new nodes) from the deep-research report. llm_assisted: true - timestamp: '2026-06-24T17:21:10Z' curator: claude action: GROUND_CAUSAL_PREDICATES changes: Grounded 4 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (RO:0002213×2, METPO:2007401×1, RO:0002327×1). llm_assisted: true - timestamp: '2026-06-24T17:21:17Z' curator: claude action: GROUND_CAUSAL_NODES changes: Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv (UniProtKB:A0A068T423×1). llm_assisted: true