TraitMech

TraitMech › ENVIRONMENT

NaCl delta low

METPO:1000479 · CLASS · REVIEWED

A NaCl delta phenotype with a narrow growth-supporting NaCl breadth of at most approximately 1% (w/v), characteristic of stenohaline organisms.

Trait evidence (1)

  • DOI:10.1093/femsre/fuy009
    salinity range

    Osmoadaptation review supports narrow salinity-tolerance breadths as the stenohaline phenotype, contrasted with euryhaline organisms.

NaCl-delta-low stenohaline breadth

DOI-backed graph linking limited osmoadaptive flexibility to a narrow NaCl growth breadth (≤ ~1% w/v).

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-low stenohaline breadth Interactive directed graph showing evidence-backed causal relationships for NaCl delta low.

Edge evidence

  • limited osmoadaptive flexibility confers NaCl delta low METPO:2007700

    Limited osmoadaptive flexibility yields a narrow NaCl-delta breadth.

  • NaCl delta low is a NaCl delta rdfs:subClassOf

    NaCl delta low is a quantitative bin of the NaCl-delta phenotype.

  • ectoine biosynthesis capacity supports NaCl delta

    Ectoine biosynthesis capacity broadens NaCl tolerance; its loss narrows the growth range.

    • DOI:10.1128/aem.01905-23 Wild-type H. elongata synthesizes ectoine as a major osmolyte, whereas ectoine-deficient strains become salt sensitive; supports general role of ectoine pathway in broadening NaCl tolerance.
  • compatible-solute transporters (Opu/ProU) supports limited osmoadaptive flexibility

    Salinity-induced Opu/ProU compatible-solute transporters underlie osmoadaptive flexibility; limited capacity contributes to narrow breadth.

    • DOI:10.1128/aem.00145-24 Proteomics showed salinity-linked increases in compatible-solute transporters (opuAC, proX/proV/proW) supporting osmoadaptation.
  • TrkH potassium uptake system supports NaCl delta

    TrkH K+ uptake supports intracellular K+ homeostasis enabling salt tolerance; its absence may contribute to narrow breadth.

    • DOI:10.1128/aem.00145-24 TrkH listed among salinity-responsive proteins; simultaneous accumulation of compatible solutes and K+ supports salt adaptation.
  • NhaC-family Na+/H+ antiporter supports NaCl delta

    NhaC Na+/H+ antiporters support ion homeostasis under salt stress; a candidate breadth-expanding mechanism whose absence may contribute to NaCl delta low.

    • DOI:10.1128/aem.00145-24 Proteomics show strong salinity-linked increases for NhaC-family antiporters (~3.27 and 3.22-fold).
  • intracellular proline accumulation supports NaCl delta

    Increased intracellular proline as a compatible solute supports growth at higher NaCl, broadening tolerance.

    • DOI:10.1128/aem.01195-24 Engineered proline biosynthesis with blocked catabolism increased intracellular proline and restored growth at 8% NaCl; supports osmolyte role of proline in salt-tolerance breadth.

Provenance

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

Parent traits (1)

Synonyms (1)

  • Nad_<=1 RELATED_SYNONYM · metpo.owl

kg-microbe context

Matched 1 kg-microbe node via direct_metpo.

  • METPO:1000479 [-3.032, -4.103, -2.404, +1.560, …]

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_low-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 delta low

## Executive summary

**Trait:** “NaCl delta low”
**Trait CURIE:** **METPO:1000479**
**Parent:** **METPO:1000335**
**Synonym:** `Nad_<=1`

This trait should represent an **assay-derived narrow breadth of NaCl concentrations supporting microbial growth**, conventionally no more than approximately **1% (w/v) NaCl** between the lower and upper growth boundaries. It is therefore a *breadth* phenotype—not the organism’s NaCl optimum, minimum, maximum, or requirement. “Stenohaline” is the ecological interpretation of this narrow breadth.

The strongest mechanistic model is that NaCl changes disturb water balance and turgor; organisms normally compensate first with K⁺ uptake and then with compatible-solute synthesis or import. Weak, absent, poorly regulated, or environmentally substrate-dependent compensation can restrict the growth window. However, direct evidence that any single gene *causes* **METPO:1000479** is scarce. Most available studies measure tolerance at one or several salt concentrations rather than a complete growth-supporting interval. Consequently, the initial TraitMech graph should emphasize proximal osmoadaptation mechanisms and retain explicit uncertainty on edges connecting those mechanisms to the final narrow-breadth phenotype.

## 1. Trait scope and boundary cases

### Recommended interpretation

A positive annotation requires growth measurements across enough NaCl concentrations to identify both boundaries of the supported-growth interval. The relevant quantity is:

> **NaCl delta = upper growth-supporting NaCl boundary − lower growth-supporting NaCl boundary**

The phenotype is **METPO:1000479** when that interval is at most approximately 1% NaCl (w/v), subject to the assay’s resolution. The threshold is about 0.171 M NaCl if converted using 58.44 g mol⁻¹, but conversion should not imply greater precision than the original assay.

### Distinguish from nearby concepts

- **Low maximum NaCl tolerance:** an organism may have a low upper limit but a broad interval below it.
- **High minimum or obligate NaCl requirement:** a halophile may fail below its minimum yet tolerate a broad high-salt interval.
- **NaCl optimum:** a narrow optimum does not establish a narrow growth interval.
- **Salt sensitivity at one dose:** inhibition at one NaCl concentration does not locate both boundaries.
- **Osmolarity tolerance:** NaCl has ionic as well as osmotic effects; sucrose or sorbitol assays are not automatically equivalent.
- **Field stenohalinity:** abundance restricted to one estuarine salinity category is an ecological proxy, not the same measurement as a ≤1% laboratory growth breadth.
- **Acclimation versus constitutive breadth:** inoculum history, compatible solutes in the medium, growth phase, and exposure rate can alter apparent boundaries.

Wu et al. defined organisms thriving within a narrow salinity range as stenohaline and euryhaline organisms as those adapting to wide fluctuations. Their operational MAG criterion was ecological: average abundance in one salinity category had to exceed both other categories by an order of magnitude. This should not be substituted for the METPO assay threshold without a mapping rule (wu2024metagenomicinsightsinto pages 1-2).

A useful physiological comparator is *Spiribacter salinus* M19-40: no growth was reported below 0.4 M NaCl, maximal growth at 0.8 M, and impaired growth at 1.0–2.0 M. That study calls its useful range narrow, but its total reported tolerated interval is much wider than 1% w/v; it is thus mechanistically informative but not necessarily a literal positive example of **METPO:1000479** (leon2018compatiblesolutesynthesis pages 4-5).

## 2. Candidate nodes grouped by type

### Trait and assay nodes

| Candidate node | Grounding | Curation note |
|---|---|---|
| NaCl delta low | **METPO:1000479** | Use verbatim as target node. |
| Parent trait | **METPO:1000335** | Preserve asserted parent relation. |
| Lower NaCl growth boundary | Label only | Assay-derived endpoint. |
| Upper NaCl growth boundary | Label only | Assay-derived endpoint. |
| Growth-supporting NaCl breadth | Label only | Calculated difference between endpoints. |
| Stenohaline ecological niche | Label only | Keep separate from the assay phenotype unless METPO explicitly equates them. |

### Environmental and experimental factors

- Extracellular NaCl concentration.
- Hyperosmotic upshift and hypoosmotic downshift.
- Medium osmolarity/osmolality.
- External compatible-solute availability.
- Exposure rate, acclimation time, temperature, pH, medium composition, and inoculum history.
- Stable versus fluctuating salinity habitat.

In *C. difficile*, 100–200 mM added NaCl had little effect, whereas 400 mM severely restricted growth; the tested media ranged from 244 to 1,023 mOsm kg⁻¹. This demonstrates strong assay-context dependence but does not by itself establish the ≤1% breadth trait (michel2022cellularadaptationof pages 2-3).

Showing the first 60 of 239 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.

  • Sphingomonas oligoaromativorans NCBITaxon:575322 DOI:10.1099/ijs.0.052894-0 Sphingomonas oligoaromativorans SY-6T grew from 0 to 0.5% (w/v) NaCl, a directly reported 0.5-point breadth wholly within the at-most-1% delta bin.

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 limited osmoadaptive flexibility to the stenohaline NaCl-delta 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. · ENRICH_CAUSAL_GRAPH · claude

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

  5. · GROUND_CAUSAL_PREDICATES · claude

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

  6. · MIGRATE_MICROBE_DOMAIN_EDGES · claude

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

  7. · MERGE_CAUSAL_NODE · claude

    Merged node salt_tolerance_breadth into nacl_delta and repointed its edges. Issue 352. A FIFTH restatement, caught in review (#360). 'Capacity to grow across a range of ambient NaCl concentrations' against nacl_delta's 'Breadth of the growth-supporting NaCl range' -- the same claim, and nacl_delta is in the same graph already TRAIT and already grounded METPO:1000335. I had retyped it and grounded it METPO:1000622 (halotolerant), which is a DEGREE of tolerance, not a breadth: 1000622 is a halophily preference (sub 1000629) while 1000335 is a delta (sub 1000532/1000534), so the node's existing `is a -> nacl_delta` edge asserted halotolerant sub NaCl delta, a subsumption METPO does not have. The absolute-vs-breadth distinction this migration insists on for pH, missed for salt.

  8. · NORMALISE_NODE_TYPE · claude

    Under the PATHWAY-vs-BIOLOGICAL_PROCESS rule, one node_id means one thing corpus-wide (issue 356): ectoine_biosynthesis is typed PATHWAY. PATHWAY is a named, conventionally enumerable multi-step route; BIOLOGICAL_PROCESS is everything else. A named route, enumerated two ways and both of them enumerations. environment/euryhaline.yaml counts five steps from L-aspartate (lysC/asd/ectB/ectA/ectC); environment/nacl_delta_mid1.yaml counts the three ectABC enzymes proper. Naming the file matters because the two differ and a bare quote would put euryhaline's wording into nacl_delta_mid1's record (#400 review). Either way the steps can be listed, which is the test. Applied AGAINST the majority, which was 4 BIOLOGICAL_PROCESS to 2 before this tranche.

  9. · 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_low_stenohaline=NONMECHANISTIC with scope_notes; marked 3 GENE_OR_PROTEIN node(s) REVIEWED_LABEL_ONLY with grounding_notes (compatible_solute_transporters, trkh_k_uptake, nhac_antiporter).

  10. · ADD_CANONICAL_EXAMPLES · codex

    Resolved issue #444 after the #591 source/bin policy with 1 direct source-backed canonical example(s): Sphingomonas oligoaromativorans (NCBITaxon:575322; DOI:10.1099/ijs.0.052894-0). The note retains the measured value or scopes broad-class examples to the cited branch; no paid research was used.