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NaCl optimum mid2

METPO:1000467 · CLASS · REVIEWED

A NaCl optimum phenotype with the best-growth NaCl concentration approximately between 3 and 8% (w/v), corresponding to moderate-halophile or halotolerant physiology.

NaCl-optimum-mid2 moderate-halophile setpoint

DOI-backed graph linking pronounced compatible-solute accumulation at elevated NaCl to a 3–8% (w/v) NaCl-optimum (moderate halophile).

NaCl-optimum-mid2 moderate-halophile setpoint Interactive directed graph showing evidence-backed causal relationships for NaCl optimum mid2.

Edge evidence

  • elevated NaCl regulates pronounced compatible-solute accumulation RO:0002211

    Elevated NaCl drives substantial compatible-solute accumulation.

    • DOI:10.1093/femsre/fuy009 synthesize organic osmotic solutes Supports compatible-solute accumulation as the osmoadaptive response at elevated NaCl.
  • pronounced compatible-solute accumulation confers NaCl optimum mid2 METPO:2007700

    Pronounced compatible-solute accumulation yields a 3–8% NaCl-optimum setpoint.

    • DOI:10.1093/femsre/fuy009 moderate halophile Supports the 3–8% optimum as the moderate-halophile outcome.
  • NaCl optimum mid2 is a NaCl optimum rdfs:subClassOf

    NaCl optimum mid2 is a quantitative bin of the NaCl-optimum phenotype.

    • DOI:10.1093/femsre/fuy009 optimal NaCl Supports the 3–8% optimum as a value within the NaCl-optimum distribution.
  • elevated NaCl induces ectoine biosynthesis module (ectABC)

    Elevated salinity (>3% NaCl) triggers the canonical ectoine biosynthesis pathway.

    • DOI:10.1128/aem.01905-23 Exposure to salt concentrations higher than 3% NaCl triggers biosynthesis and intracellular accumulation of ectoine as a major compatible solute (Zou et al. 2024).
  • elevated NaCl upregulates ectoine biosynthesis module (ectABC)

    Salt stress at ~6% w/v NaCl (within the 3-8% window) upregulates the ectoine biosynthesis module.

    • DOI:10.1186/s12934-024-02515-w Transcriptomics showed the ectoine biosynthesis module is upregulated under salt stress, with 60 g/L NaCl (~6% w/v, inside 3-8% window) optimal for growth (Chen et al. 2024).
  • ectoine biosynthesis module (ectABC) has output ectoine RO:0002234

    The ectABC pathway synthesizes the compatible solute ectoine.

    • DOI:10.1128/aem.01905-23 Biosynthesis and intracellular accumulation of ectoine as a major compatible solute via the ectoine pathway (Zou et al. 2024).
  • pronounced compatible-solute accumulation is a compatible-solute strategy rdfs:subClassOf

    Pronounced organic-osmolyte accumulation is an instance of the compatible-solute osmoadaptation strategy.

    • DOI:10.3390/biotech14020049 The compatible-solute strategy accumulates small organic osmolytes including glycine, betaine, and ectoine (Neagu & Stancu 2025).
  • compatible-solute strategy uses ectoine

    Compatible-solute osmoadaptation employs ectoine as an organic osmolyte.

    • DOI:10.1186/s12934-025-02757-2 Many species naturally produce the osmolyte ectoine (plus hydroxyectoine, betaine, glycine, proline) (Coimbra et al. 2025).
  • compatible-solute strategy uses glycine betaine

    Compatible-solute osmoadaptation employs glycine betaine as an organic osmolyte.

    • DOI:10.3390/biotech14020049 Identified compatible solutes include glycine, betaine, and ectoine (Neagu & Stancu 2025).
  • compatible-solute strategy uses L-proline

    Compatible-solute osmoadaptation employs L-proline as an organic osmolyte.

    • DOI:10.1186/s12934-025-02757-2 Many species naturally produce the osmolyte ectoine plus hydroxyectoine, betaine, glycine, proline (Coimbra et al. 2025).

Provenance

Source
METPO (2025-11-25)
Definition source
DOI:10.1093/femsre/fuy009

Parent traits (1)

Synonyms (3)

  • Halotolerant EXACT_SYNONYM · metpo.owl
  • Moderate halophile EXACT_SYNONYM · metpo.owl
  • NaO_3_to_8 RELATED_SYNONYM · metpo.owl

kg-microbe context

Matched 1 kg-microbe node via direct_metpo.

  • METPO:1000467 [-0.989, -0.801, -1.139, +3.616, …]

512-dim DeepWalkSkipGramEnsmallen embedding from kg-microbe (2026-04-25).

Nearest neighbors in embedding space

Top-8 cosine-similar METPO traits from the 2026-04-25 deepwalk (512-D).

Deep research

Generated by just research-trait; source: research/traits/environment/nacl_optimum_mid2-deep-research-falcon.md

Unreviewed literature output — not curated TraitMech content Ontology identifiers suggested below have not been resolved against their ontologies, and some are known to be wrong. Check any CURIE against the source before using it. 
# Curation report: NaCl optimum mid2

## 1. Scope summary

**Target:** **NaCl optimum mid2**  
**Trait identifier:** **METPO:1000467**  
**Parent:** METPO:1000333  
**Category/kind/status:** ENVIRONMENT / CLASS / REVIEWED

This trait should represent an **organism-level growth optimum**, operationally defined as best growth at approximately **3–8% (w/v) NaCl**. It is not equivalent to survival, maximum tolerated salinity, broad halotolerance, growth range, or induction of a salt-stress response. The preferred evidence is a growth-rate or biomass-yield curve measured across several NaCl concentrations under otherwise fixed conditions.

A useful physiological anchor is *Spiribacter salinus* M19-40: no growth was detected through 0.4 M NaCl, growth was strongly stimulated up to an optimum near 0.8 M, and progressively impaired from 1.0 to 2.0 M. Because 0.8 M NaCl is approximately 4.7% (w/v), this is a direct example inside the target interval. Its viable range extended well beyond its optimum, illustrating why optimum and tolerance must remain separate graph concepts (leon2018compatiblesolutesynthesis pages 4-5).

### Boundary cases

- **Lower boundary:** organisms growing best below approximately 3% NaCl should not receive this trait merely because they tolerate 3–8%.
- **Upper boundary:** an optimum reported as exactly 8% is within the supplied approximate definition, but should retain the measured value and assay conditions. Optima above 8% should normally map to a higher-salinity class.
- **Halotolerant versus halophilic:** “halotolerant” is not always synonymous with a 3–8% optimum; many halotolerant organisms grow optimally without added salt. The synonym should therefore be treated as a search term, not an independently sufficient annotation.
- **NaCl versus total salts or Na⁺:** results stated in total dissolved salts, molar Na⁺, seawater salinity, or another chloride salt are not automatically equivalent to % (w/v) NaCl.
- **Assay dependence:** medium composition, compatible solutes, carbon source, temperature, pH, oxygen status, inoculum history, and whether optimum means growth rate or final yield can move the apparent optimum.

## 2. Current mechanistic interpretation

Moderately halophilic and halotolerant bacteria usually employ a predominantly **“salt-out” strategy**: rapid K⁺ uptake and ion-homeostasis responses are followed by accumulation of compatible organic solutes, allowing cytoplasmic osmotic balance without maintaining extremely high concentrations of disruptive inorganic salts. The strongest trait-proximal evidence currently supports **ectoine and proline accumulation** as alternative sufficient osmolyte solutions in *Halomonas elongata*.

In a 2024 genetic-engineering experiment, an ectoine-deficient *H. elongata* strain could not grow above 4% NaCl. Replacing `ectABC` with an engineered `proBm1AC` cluster and deleting the proline-catabolic gene `putA` generated intracellular proline accumulation of **353.1 ± 40.5 µmol g⁻¹ fresh cells** and restored robust growth at **8% NaCl**. This provides unusually strong perturbational evidence that intracellular compatible-solute accumulation causally supports growth at the upper boundary of METPO:1000467, while also showing that the specific osmolyte is partly substitutable (khanh2024metabolicpathwayengineering pages 1-2).

In *S. salinus*, intracellular ectoine increased from approximately **80 µM at 0.6 M NaCl** to **170 µM at the 0.8 M optimum**. Trehalose was much less abundant and was interpreted as a minor contributor. Exogenous compatible-solute assays found glycine betaine and arsenobetaine among the strongest osmoprotectants, supporting import as an alternative to de novo synthesis (leon2018compatiblesolutesynthesis pages 10-11).

## 3. Candidate nodes

### Trait and environmental nodes

- **NaCl optimum mid2 — METPO:1000467**
- **NaCl optimum phenotype** — parent supplied as METPO:1000333
- Sodium chloride — use a verified ChEBI record during implementation; do not assign an unchecked CURIE
- NaCl concentration, 3–8% (w/v)
- Extracellular osmolarity / hyperosmotic stress
- Growth rate, biomass yield, and growth optimum
- Medium composition, temperature, pH, oxygen regime, incubation time

### Chemicals and metabolites

- Sodium ion — **CHEBI:29101**
- Potassium ion — **CHEBI:29103**
- Chloride — **CHEBI:17996**
- L-proline — **CHEBI:17203**
- L-glutamate — **CHEBI:29985**
- Glycine betaine — candidate ChEBI grounding should be registry-verified before YAML insertion
- Ectoine — candidate ChEBI grounding should be registry-verified
- 5-hydroxyectoine — label-only until verified
- Trehalose — **CHEBI:27082**
- Glutathione — **CHEBI:16856**
- Water

### Genes, proteins, and complexes

- `ectA`, `ectB`, `ectC`; **EctABC ectoine-biosynthesis module**
- `proB`, `proA`, `proC`; proline-biosynthesis module
- Engineered feedback-insensitive `proBm1AC`

Showing the first 60 of 204 lines of findings; the linked file also carries the run's front matter and the prompt it was given — read the full report.

Curation history

  1. · SEEDED_FROM_METPO · seed_from_metpo

    imported from data/raw/metpo.owl (CLASS)

  2. · CURATED_CAUSAL_GRAPH · claude

    Added DOI-backed definition and causal graph linking pronounced compatible-solute accumulation at elevated NaCl to the moderate-halophile NaCl-optimum bin.

  3. · GROUND_CAUSAL_PREDICATES · claude

    Grounded 2 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (METPO:2000202×1, rdfs:subClassOf×1).

  4. · RENAME_PREDICATE_LABELS · claude

    Renamed 1 causal-edge predicate label(s) to align with existing groundings: drives → regulates ×1.

  5. · GROUND_CAUSAL_PREDICATES · claude

    Grounded 1 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (RO:0002211×1).

  6. · ENRICH_CAUSAL_GRAPH · claude

    Added 7 evidence-backed generic edges (5 new nodes) from the deep-research report.

  7. · GROUND_CAUSAL_PREDICATES · claude

    Grounded 2 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (METPO:2000202×1, rdfs:subClassOf×1).

  8. · GROUND_CAUSAL_NODES · claude

    Grounded 2 causal-node grounding field(s) via mappings/node_grounding.tsv (CHEBI:27592×1, CHEBI:17750×1).

  9. · MIGRATE_MICROBE_DOMAIN_EDGES · claude

    Re-grounded 2 causal edge(s) off microbe-domain METPO predicates (1 to confers, 1 to has output), issue 301. The previous predicates are transitively rdfs:subPropertyOf METPO:2000001, whose rdfs:domain is METPO:1000525 (microbe), so a causal-graph subject entailed that the subject IS a microbe; CausalNodeTypeEnum has no organism member, so no such edge could ever satisfy the domain. Edge directions are unchanged - this pass only relabels and re-grounds. RO:0002234 (has output) is used where the subject is an activity, since biolink gives it the domain 'biological process or activity'; the METPO replacements are proposed in proposals/metpo_traitmech_v8 and v9 and are placeholder ids until METPO mints them.