identifier: METPO:1000628
label: extremely halophilic
definition: A halophily preference in which an organism requires very high salt concentrations
  (typically 15-30% NaCl or higher) for optimal growth and cannot grow at salt concentrations
  below approximately 12%.
definition_source: PMID:11790755
trait_category: ENVIRONMENT
term_kind: CLASS
mapping_status: REVIEWED
parent_traits:
- METPO:1000629
synonyms:
- synonym_text: extreme-halophilic
  synonym_type: RELATED_SYNONYM
  source: metpo.owl
created_by: Jed Dongjin Kim-Ozaeta
evidence:
- reference: PMID:11790755
  snippet: A cytochrome in an extremely halophilic archaeon, Haloferax volcanii
  notes: 'Organism example: Haloferax volcanii is described as extremely halophilic.'
canonical_examples:
- taxon_id: NCBITaxon:2242
  taxon_label: Halobacterium salinarum
  note: "Classic extreme-halophile model requiring near-saturating NaCl; twin lab strains NRC-1 (NCBITaxon:64091) and R1 (NCBITaxon:478009)."
  reference: https://pmc.ncbi.nlm.nih.gov/articles/PMC10264941/
causal_graphs:
- graph_id: extreme_halophile_salt_in_acidic_proteome
  title: Extreme halophile salt-in and acidic-proteome mechanism
  description: Evidence-backed causal sketch linking extreme halophily to saturated
    salt environments, intracellular KCl, and salt-adapted acidic proteins.
  nodes:
  - node_id: extremely_halophilic_trait
    label: extremely halophilic
    node_type: TRAIT
    grounding: METPO:1000628
    description: Optimal growth requires very high salt concentrations.
  - node_id: hypersaline_brine
    label: hypersaline brine
    node_type: ENVIRONMENTAL_FACTOR
    description: High-salt or near-saturating brine environment.
  - node_id: potassium_ion
    label: potassium ion
    node_type: CHEMICAL
    grounding: CHEBI:29103
    description: K+ accumulated intracellularly in salt-in osmoadaptation.
  - node_id: salt_in_strategy
    label: salt-in strategy
    node_type: BIOLOGICAL_PROCESS
    description: Intracellular inorganic salt accumulation for osmotic balance.
    grounding: METPO:1007720
  - node_id: acidic_halophilic_proteins
    label: acidic halophilic proteins
    node_type: GENE_OR_PROTEIN
    description: Proteins enriched in acidic residues and adapted to high ionic strength.
  - node_id: osmotic_stress
    label: osmotic stress
    node_type: BIOLOGICAL_PROCESS
    description: Cellular response to high external solute/osmotic pressure.
    grounding: GO:0006970
  - node_id: na_h_antiporter
    label: Na+/H+ antiporter
    node_type: GENE_OR_PROTEIN
    description: Membrane transporter mediating sodium exclusion in exchange for protons.
    grounding: UniProtKB:A0A068T423
  - node_id: sodium_efflux
    label: sodium efflux
    node_type: BIOLOGICAL_PROCESS
    description: Active export of Na+ to maintain low cytoplasmic sodium.
  - node_id: protein_solubility_high_salt
    label: protein solubility and function in high salt
    node_type: QUALITY
    description: Maintenance of protein solubility and activity in hypersaline cytoplasm.
  - node_id: s_layer_n_glycosylation
    label: S-layer glycoprotein N-glycosylation
    node_type: BIOLOGICAL_PROCESS
    description: N-linked glycosylation of the S-layer glycoprotein in haloarchaea.
  - node_id: s_layer_stability
    label: S-layer stability
    node_type: QUALITY
    description: Structural stability of the haloarchaeal S-layer cell envelope.
  edges:
  - subject: hypersaline_brine
    predicate: selects for
    object: extremely_halophilic_trait
    description: Extreme halophiles are adapted to growth in hypersaline brines.
    evidence:
    - reference: DOI:10.1093/femsre/fuy009
      snippet: salt concentrations up to NaCl saturation
      notes: Review supports saturated salt environments as extreme-halophile habitats.
    predicate_id: METPO:2007401
  - subject: salt_in_strategy
    predicate: uses
    object: potassium_ion
    description: Extreme haloarchaea often balance osmotic pressure by accumulating
      intracellular KCl.
    evidence:
    - reference: DOI:10.1093/femsre/fuy009
      snippet: KCl accumulating Halobacterium salinarum
      notes: Supports KCl accumulation as a model salt-in strategy.
  - subject: salt_in_strategy
    predicate: enables
    object: extremely_halophilic_trait
    description: Maintaining high intracellular salt supports growth at extreme external
      salinity.
    evidence:
    - reference: DOI:10.1038/srep25642
      snippet: Salt-in strategy
      notes: Haloarchaeal salinity-stress study describes salt-in adaptation in extreme
        halophiles.
    predicate_id: RO:0002327
  - subject: acidic_halophilic_proteins
    predicate: enables
    object: extremely_halophilic_trait
    description: Acidic proteins remain soluble and functional in high salt.
    evidence:
    - reference: DOI:10.1016/j.copbio.2015.05.004
      snippet: negatively charged due to an excess of acidic over basic residues
      notes: Review supports acidic proteomes as a molecular adaptation to hypersaline
        cytoplasm.
    predicate_id: RO:0002327
  - subject: salt_in_strategy
    predicate: requires adaptation of
    object: acidic_halophilic_proteins
    description: Intracellular salt accumulation requires proteins adapted to high
      ionic strength.
    evidence:
    - reference: DOI:10.1016/j.copbio.2015.05.004
      snippet: promote function in low water activity conditions
      notes: Supports functional coupling between high-salt cytoplasm and salt-adapted
        proteins.
  - subject: hypersaline_brine
    predicate: causes
    object: osmotic_stress
    description: High external NaCl imposes osmotic stress on the cell.
    evidence:
    - reference: DOI:10.1186/s12934-024-02358-5
      notes: NaCl shock induced osmotic stress; environmental-to-stress edge broadly
        applicable.
    predicate_id: biolink:causes
  - subject: osmotic_stress
    predicate: induces
    object: potassium_ion
    description: Osmotic stress triggers rapid intracellular K+ uptake/accumulation.
    evidence:
    - reference: DOI:10.1186/s12934-024-02358-5
      notes: Many microbes rapidly uptake K+ as an emergency osmoadaptation response.
  - subject: na_h_antiporter
    predicate: mediates
    object: sodium_efflux
    description: Na+/H+ antiporters drive sodium exclusion from the cytoplasm.
    evidence:
    - reference: DOI:10.3390/microorganisms12081738
      notes: Sodium exclusion is mediated largely by Na+/H+ antiporters (general haloarchaeal
        review).
  - subject: acidic_halophilic_proteins
    predicate: supports
    object: protein_solubility_high_salt
    description: Surface acidic residues maintain protein solubility and function
      at high ionic strength.
    evidence:
    - reference: DOI:10.3390/microorganisms12081738
      notes: Halophilic proteins have increased surface acidic residues maintaining
        solubility and function in high salt.
  - subject: s_layer_n_glycosylation
    predicate: supports
    object: s_layer_stability
    description: N-glycosylation stabilizes the haloarchaeal S-layer.
    evidence:
    - reference: DOI:10.3390/v15071469
      notes: N-glycosylation supports protein folding/stability and specifically stabilizes
        the S-layer.
  - subject: hypersaline_brine
    predicate: changes
    object: s_layer_n_glycosylation
    description: External salinity alters S-layer glycoprotein N-glycosylation pathways.
    evidence:
    - reference: DOI:10.3390/v15071469
      notes: Growth at different salt concentrations alters S-layer glycoprotein N-glycosylation;
        two distinct pathways process it upon salinity changes.
curation_history:
- timestamp: '2026-05-05T01:35:46.865176+00:00'
  curator: seed_from_metpo
  action: SEEDED_FROM_METPO
  changes: imported from data/raw/metpo.owl (CLASS)
  llm_assisted: false
- timestamp: '2026-05-06T14:15:44-07:00'
  curator: codex
  action: CURATED_WITH_ORGANISM_EXAMPLE
  changes: Added Haloferax volcanii organism example with PMID-backed evidence.
  llm_assisted: true
- timestamp: '2026-05-10T00:00:00-07:00'
  curator: codex
  action: ADDED_CAUSAL_GRAPH
  changes: Added DOI-backed causal graph for extreme halophile salt-in and acidic-proteome
    adaptation.
  llm_assisted: true
- timestamp: '2026-05-20T03:35:29Z'
  curator: claude
  action: GROUND_CAUSAL_PREDICATES
  changes: Grounded 2 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv
    (RO:0002327×2).
  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: '2026-06-17T04:09:43Z'
  curator: claude
  action: REMOVE_REDUNDANT_SYNONYM
  changes: Removed 1 synonym(s) whose text duplicated the label (seeder redundancy;
    no information lost).
  llm_assisted: true
- timestamp: '2026-06-23T00:00:00Z'
  curator: claude
  action: ENRICH_CAUSAL_GRAPH
  changes: Added 6 evidence-backed generic edges (6 new nodes) from the deep-research
    report.
  llm_assisted: true
- timestamp: '2026-06-24T17:21:09Z'
  curator: claude
  action: GROUND_CAUSAL_PREDICATES
  changes: Grounded 1 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv
    (biolink:causes×1).
  llm_assisted: true
- timestamp: '2026-06-24T17:21:16Z'
  curator: claude
  action: GROUND_CAUSAL_NODES
  changes: Grounded 2 causal-node grounding field(s) via mappings/node_grounding.tsv
    (GO:0006970×1, UniProtKB:A0A068T423×1).
  llm_assisted: true