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NaCl delta

METPO:1000335 · CLASS · REVIEWED

A salinity phenotype with numerical limits expressing the breadth (maximum minus minimum) of NaCl concentrations supporting growth of an organism.

Trait evidence (2)

  • DOI:10.1093/femsre/fuy009
    salinity range

    Osmoadaptation review supports the span of NaCl-tolerance as a halophily descriptor; its breadth (delta) reflects euryhaline versus stenohaline physiology.

  • DOI:10.1186/1746-1448-4-2
    cope with the high salt concentrations

    Saline-Systems review supports broad osmoadaptive capacity as the basis of a wide NaCl-delta phenotype.

NaCl-delta euryhaline tolerance breadth

DOI-backed graph linking osmoadaptive flexibility to the breadth of the NaCl growth range (delta = max − min).

NONMECHANISTIC · This record is a quantitative measurement, interval, or bin in the environmental phenotype hierarchy; a token protein example would misrepresent the measured value as one inherited molecular mechanism.

NaCl-delta euryhaline tolerance breadth Interactive directed graph showing evidence-backed causal relationships for NaCl delta.

Edge evidence

  • osmoadaptive flexibility enables euryhaline physiology RO:0002327

    Osmoadaptive flexibility enables euryhaline growth.

    • DOI:10.1186/1746-1448-4-2 cope with the high salt concentrations Supports osmoadaptive flexibility as the basis of broad-salinity growth.
  • euryhaline physiology has output tolerance breadth RO:0002234

    Euryhaline physiology produces a wide growth-supporting NaCl range.

  • tolerance breadth manifests as NaCl delta METPO:2007400

    The breadth between minimum and maximum growth-supporting NaCl manifests the NaCl-delta phenotype.

  • compatible solute accumulation enables response to osmotic stress RO:0002327

    Compatible-solute uptake or synthesis enables osmoadaptation after an osmotic upshift.

    • DOI:10.1371/journal.pgen.1007574 secondary response involving uptake or synthesis of compatible solutes Verified against the open Pham et al. introduction; compatible-solute uptake and synthesis are retained as a broad bacterial osmotic-upshift response.
  • hyperosmotic upshift causes potassium ion uptake biolink:causes

    Hyperosmotic upshift triggers rapid K+ import as an early osmoadaptive response.

    • DOI:10.1371/journal.pgen.1007574 In response to an osmotic upshift (hyperosmotic stress), bacteria import potassium ions Verified against the open Pham et al. introduction; K+ uptake is retained as the immediate bacterial response to hyperosmotic stress.
  • potassium ion uptake contributes to response to osmotic stress RO:0002326

    K+ accumulation is a core early osmoadaptive response to increased NaCl.

    • DOI:10.1371/journal.pgen.1007574 This allows the cell to limit the loss of water and maintain turgor Verified against the open Pham et al. introduction; the early K+ import and later compatible-solute response are framed as limiting water loss and maintaining turgor.
  • compatible solute accumulation part of salt-out strategy biolink:part_of

    Compatible-solute import or synthesis is part of the salt-out osmoadaptation strategy.

    • DOI:10.3390/microorganisms12081738 The second phase starts with the import or de novo synthesis of the compatible solute Verified against public Bonnaud et al. text; the edge is reversed to ground the component-process relation.
  • salt-in strategy contributes to high maximal NaCl tolerance RO:0002326

    The salt-in strategy contributes to growth under very high ambient NaCl in haloarchaeal lineages.

    • DOI:10.3390/microorganisms12081738 haloarchaea favors the salt-in strategy at high salt concentrations in the medium Verified against public Bonnaud et al. text; salt-in is retained as a high-salt osmoadaptation strategy, not as a direct determinant of an exact NaCl-delta interval.
  • mechanosensitive channels (MscL/MscS) mitigates hypoosmotic shock METPO:2007407

    Mechanosensitive channels mitigate turgor stress during sudden hypoosmotic shocks at the low-salinity end of the range.

    • DOI:10.3390/microorganisms12081738 mechanosensitive channels, which serve as safety valves Verified against public Bonnaud et al. text; the broad MscL/MscS label is kept reviewed-label-only in this nonmechanistic quantitative graph.

Provenance

Identifier source
METPO (2026-06-12)
Definition source
DOI:10.1093/femsre/fuy009

Parent traits (2)

Children (4)

kg-microbe context

Matched 1 kg-microbe node via direct_metpo.

  • METPO:1000335 [-3.596, -2.760, -3.043, +0.053, …]

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_delta-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: microbial **NaCl delta**

## Executive summary

**Trait:** **NaCl delta**
**Identifier:** **METPO:1000335**
**Category:** ENVIRONMENT; **term kind:** CLASS; **mapping:** REVIEWED

NaCl delta is an assay-derived breadth trait:

\[
\text{NaCl delta}=\text{maximum NaCl supporting growth}-\text{minimum NaCl supporting growth}.
\]

It is therefore a property of the **entire observed growth interval**, not simply salt tolerance, the optimum NaCl concentration, or the maximum tolerated concentration. Biologically, a large delta approximates euryhaline physiology, whereas a small delta approximates stenohaline specialization. Current evidence supports a graph in which regulated compatible-solute uptake/synthesis and ion transport preserve osmotic and ionic homeostasis at the high-salinity boundary, while the salt dependence of proteins and other cellular structures can raise the low-salinity boundary. Only mechanisms affecting one or both boundaries can ultimately alter the delta.

The strongest graph-level interpretation is that flexible “salt-out” physiology often supports a broad salinity interval, whereas obligate “salt-in” specialization can constrain low-salt growth because its proteins require high intracellular salt. This is an authoritative synthesis, but it is not a universal rule: some organisms combine both strategies, and most mechanistic experiments measure high-salt growth rather than delta directly. (oren2008microbiallifeat pages 10-11, saum2008regulationofosmoadaptation pages 1-2, xing2024thepolyextremophilenatranaerobius pages 1-2)

---

## 1. Trait scope and boundary rules

### 1.1 Included phenotype

Curate **METPO:1000335** when a study reports—or permits calculation of—the difference between the highest and lowest **NaCl concentrations at which microbial growth occurs under one defined protocol**. The growth criterion may be optical density increase, colony formation, biomass, cell-number increase, or another validated proliferation endpoint, but the same criterion should define both limits.

The euryhaline/stenohaline distinction is conceptually aligned with this trait. A 2024 estuarine study defines stenohaline organisms as thriving within a narrow salinity range and euryhaline organisms as adapting to wide salinity fluctuations. However, its operational classification used environmental relative abundance rather than laboratory NaCl growth endpoints, so those labels are ecological proxies—not direct METPO:1000335 measurements. (wu2024metagenomicinsightsinto pages 1-2)

### 1.2 Nearby traits that must remain separate

| Nearby observation | Why it is not NaCl delta |
|---|---|
| Minimum NaCl for growth | One endpoint only; may reflect obligate halophily or low-salt instability. |
| Maximum NaCl for growth | One endpoint only; represents the upper growth limit. |
| Optimal NaCl | Position of best growth, not interval width. |
| Growth rate or yield at one NaCl level | Performance at a point, not breadth. |
| Survival after salt shock | Viability is not necessarily growth. |
| Generic “salt tolerance” | Often lacks both numerical limits. |
| Osmolarity range produced with sucrose or other solutes | Not specifically an NaCl interval; ionic and osmotic effects differ. |
| Seawater percentage or total salinity | Curatable only with an explicit conversion to NaCl-equivalent concentration and adequate medium description. |
| Environmental occurrence across a salinity gradient | Evidence of realized niche breadth, not necessarily intrinsic NaCl growth breadth. |

NaCl concentration changes both water activity/osmotic pressure and Na⁺/Cl⁻ chemistry. Hyperosmotic conditions drive water out of cells, causing dehydration and altered turgor; accordingly, an NaCl assay cannot automatically be interpreted as a pure osmolarity assay. (yang2024structureandmechanism pages 1-2)

### 1.3 Assay metadata required for defensible delta values

Record the strain, medium composition, NaCl units, concentration series and step size, temperature, pH, oxygen regime, incubation time, inoculum, growth threshold, and whether osmoprotectants were supplied. Also retain minimum and maximum values as separate provenance-bearing observations. A reported delta is resolution-limited: if concentrations were tested every 0.5 M, both boundaries—and hence the delta—are interval-censored by the assay grid.

A useful example is *Spiribacter salinus* M19-40: no growth was detected below 0.4 M NaCl, optimum growth occurred at 0.8 M, and growth was observed over approximately 0.6–2.0 M. Under that protocol, the observed delta is approximately **1.4 M**, but the true lower and upper limits are only bounded by the tested series. (leon2018compatiblesolutesynthesis pages 4-5)

---

## 2. Current mechanistic model

A tractable TraitMech graph should distinguish three levels:

1. **Primary stress:** increased extracellular NaCl → water efflux, dehydration, turgor perturbation, Na⁺ stress.
2. **Homeostatic responses:** compatible-solute accumulation, K⁺ uptake, Na⁺ extrusion, regulated transport, metabolic and proteome adaptation.
3. **Boundary effects:** restored growth at high NaCl lowers growth inhibition at the upper boundary; salt-dependent proteins or structures can prevent low-NaCl growth and raise the lower boundary. The resulting difference determines **METPO:1000335**.

Showing the first 60 of 300 lines of findings; the linked file also carries the run's front matter and the prompt it was given — read the full report.

Canonical examples (1)

Organisms cited as exemplars of this trait. Taxon ids are NCBITaxon and link out to the NCBI record.

  • Lederbergia graminis NCBITaxon:735518 DOI:10.1099/ijs.0.023820-0 The type strain, published as Bacillus graminis YC6957T, grew at 0-8% (w/v) NaCl. Its 8-point breadth meets a bin boundary, so #591 keeps this claim on the delta parent.

Curation history

  1. · SEEDED_FROM_METPO · seed_from_metpo

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

  2. · CURATED_CAUSAL_GRAPH · claude

    Added DOI-backed causal graph linking osmoadaptive flexibility and euryhaline physiology to the NaCl-delta breadth phenotype.

  3. · GROUND_CAUSAL_PREDICATES · claude

    Grounded 2 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (RO:0002327×1, METPO:2000202×1).

  4. · GROUND_CAUSAL_PREDICATES · claude

    Grounded 1 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (METPO:2007400×1).

  5. · ENRICH_CAUSAL_GRAPH · claude

    Added 6 evidence-backed generic edges (9 new nodes) from the deep-research report.

  6. · GROUND_CAUSAL_PREDICATES · claude

    Grounded 3 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (RO:0002327×1, biolink:causes×1, RO:0002326×1).

  7. · GROUND_CAUSAL_NODES · claude

    Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv (METPO:1007720×1).

  8. · GROUND_CAUSAL_NODES · claude

    Grounded 2 causal-node grounding field(s) via mappings/node_grounding.tsv (GO:1990573×1, GO:0006970×1).

  9. · MIGRATE_MICROBE_DOMAIN_EDGES · claude

    Re-grounded 1 causal edge(s) off microbe-domain METPO predicates (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.

  10. · NORMALISE_NODE_TYPE · claude

    Under the PATHWAY-vs-BIOLOGICAL_PROCESS rule, one node_id means one thing corpus-wide (issue 356): salt_in_strategy is typed BIOLOGICAL_PROCESS. PATHWAY is a named, conventionally enumerable multi-step route; BIOLOGICAL_PROCESS is everything else. A STRATEGY, not a route. The family is described as osmoadaptation by accumulating intracellular inorganic ions -- haloalkaliphilic.yaml puts it as 'Osmoadaptation by intracellular accumulation of inorganic ions (e.g. K+)', and the wording varies by record. There is no step list to enumerate, which is exactly the distinction this rule draws. Was 7 BIOLOGICAL_PROCESS to 1 before this tranche.

  11. · REVIEW_GRAPH_PROTEIN_TAXON · claude

    Backfilled provenance (review issue 517) for the codex protein-taxon review tranche of 2026-08-24/25, which shipped without a per-record event. In this record the tranche: set graph scope nacl_delta_euryhaline_breadth=NONMECHANISTIC with scope_notes; marked 1 GENE_OR_PROTEIN node(s) REVIEWED_LABEL_ONLY with grounding_notes (mechanosensitive_channels).

  12. · ADD_CANONICAL_EXAMPLES · codex

    Resolved issue #444 after the #591 source/bin policy with 1 direct source-backed canonical example(s): Lederbergia graminis (NCBITaxon:735518; DOI:10.1099/ijs.0.023820-0). The note retains the measured value or scopes broad-class examples to the cited branch; no paid research was used.

  13. · REVIEW_CAUSAL_EVIDENCE · codex

    Reviewed the nacl_delta_euryhaline_breadth graph for issue #183: added exact snippets to 6 causal-edge evidence items, grounded 3 residual predicates, and preserved the graph as a nonmechanistic quantitative NaCl-range-breadth classification. No paid research service was called.