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pH delta mid3

METPO:1000477 · CLASS · REVIEWED

A pH delta phenotype with a growth-supporting pH breadth of approximately 4–5 pH units, characteristic of organisms with wide pH-tolerance breadth.

Trait evidence (1)

  • DOI:10.1038/nrmicro2549
    pH homeostasis

    pH-homeostasis review supports wide pH-homeostasis flexibility as the basis of euryphilic pH-tolerance.

pH-delta-mid3 wide pH-homeostasis context

DOI-backed nonmechanistic graph annotating wide pH-homeostasis flexibility, PMF regulation and generation, alkaline Na+/H+ antiport, ATPase support, phosphate buffering, amino-acid decarboxylation, and membrane proton-permeability branches to the 4-5 pH-unit breadth bin.

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.

pH-delta-mid3 wide pH-homeostasis context Interactive directed graph showing evidence-backed causal relationships for pH delta mid3.

Edge evidence

  • wide pH-homeostasis flexibility confers pH delta mid3 METPO:2007700

    Wide pH-homeostasis flexibility yields a 4–5 pH-unit pH-delta breadth.

  • pH delta mid3 is a pH delta rdfs:subClassOf

    pH delta mid3 is a quantitative bin of the pH-delta phenotype.

    • DOI:10.1038/nrmicro2549 tolerate or grow at external pH values that are outside the cytoplasmic pH range Verified against the open PMC manuscript of the Krulwich et al. review; pH breadth is represented as a quantitative external-growth-pH bin under the pH-delta phenotype.
  • external alkaline pH regulates electrogenic Na+/H+ antiport RO:0002211

    High external pH modulates the contribution of electrogenic Na+/H+ antiport to cytoplasmic pH homeostasis.

    • DOI:10.1038/nrmicro2549 For pH homeostasis under alkaline conditions, active transport of protons inward is a crucial adaptation, which usually involves activation and transcriptional up-regulation of key cation/proton antiporters Verified against the open PMC manuscript of the Krulwich et al. review; cation/proton antiporters use PMF from respiration or ATPases to drive proton uptake under alkaline stress.
  • regulation of membrane potential and pH gradient contributes to cytoplasmic pH maintenance RO:0002326

    Regulation of Delta-psi and Delta-pH contributes to maintenance of cytoplasmic pH across external pH changes.

    • DOI:10.1038/nrmicro2549 the demands of pH homeostasis for particular bacteria determine the relative magnitudes of the two PMF components Verified against the open PMC manuscript of the Krulwich et al. review; bacterial pH-homeostasis demands determine how delta-psi and delta-pH contribute to the PMF.
  • proton-pumping respiratory complexes generates proton motive force biolink:produces

    Proton-pumping respiratory complexes generate proton motive force.

    • DOI:10.1038/nrmicro2549 Primary proton pumps generate the PMF Verified against the open PMC manuscript of the Krulwich et al. review; respiratory-chain complexes are listed among the proton pumps that establish bacterial PMF.
  • F0F1-ATPase contributes to cytoplasmic pH maintenance RO:0002326

    F0F1-ATPase proton pumping contributes to bacterial pH homeostasis.

    • DOI:10.1093/femsre/fuad033 the F0F1-ATPase (fermentative bacteria), or decarboxylation pathways (next paragraph) prevent the internal pH from becoming too low Verified against the open Poolman review; proton-pumping enzymes, including F0F1-ATPase in lactic acid bacteria, are listed as bacterial pH-homeostasis regulators.
  • cytoplasmic phosphate buffering contributes to intracellular pH stability RO:0002326

    Cytoplasmic phosphate buffering contributes to intracellular pH stability.

    • DOI:10.1093/femsre/fuad033 sufficient buffering capacity (e.g. inorganic and organic phosphates) Verified against the open Poolman review; cytoplasmic phosphate pools are named as sufficient buffering capacity needed for internal-pH stability.
  • amino-acid decarboxylation pathways contributes to proton motive force RO:0002326

    Amino-acid decarboxylation pathways consume protons and contribute to PMF and intracellular pH control.

    • DOI:10.1093/femsre/fuad033 free energy change from decarboxylation reactions can be stored in the form of a proton motive force Verified against the open Poolman review; substrate decarboxylation is linked to bacterial PMF generation in pH homeostasis.
  • membrane lipid composition shifts decreases membrane proton permeability RO:0002212

    Membrane lipid composition shifts reduce proton permeability.

    • DOI:10.3389/fmicb.2022.1034164 required a saturated membrane to minimize proton permeability in an extremely acidic environment Verified against the open Frontiers methanotroph review; saturated bacterial membranes are described as lowering proton permeability under acid stress.

Provenance

Identifier source
METPO (2026-06-12)
Definition source
DOI:10.1038/nrmicro2549

Parent traits (1)

Synonyms (1)

  • pHd_4_5 RELATED_SYNONYM · metpo.owl

kg-microbe context

Matched 1 kg-microbe node via direct_metpo.

  • METPO:1000477 [-3.578, -1.920, -3.431, +0.231, …]

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/ph_delta_mid3-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-focused research report: pH delta mid3

**Target trait:** **pH delta mid3**
**Trait identifier:** **METPO:1000477**
**Category / kind / status:** ENVIRONMENT / CLASS / REVIEWED
**Supplied synonym:** `pHd_4_5`
**Parent:** METPO:1000232

## Executive conclusion

METPO:1000477 should be interpreted as an **assay-observed growth breadth**, namely an organism’s upper growth-supporting external-pH boundary minus its lower boundary being approximately **4–5 pH units**. It is not the optimum pH, environmental pH preference, cytoplasmic-pH range, or survival after a short lethal-pH challenge.

The strongest mechanistic interpretation is that wide breadth emerges from coordinated **cytoplasmic pH homeostasis**, combining acid-side proton exclusion/consumption and damage control with alkaline-side proton acquisition. The literature strongly supports the individual modules, but the sources reviewed do **not** establish that any one module causes the specific 4–5-unit phenotype. Accordingly, most direct module → METPO:1000477 edges should remain hypotheses until paired growth-range and perturbation data are available.

## 1. Trait scope and boundaries

### Positive operational definition

For curation, require growth measurements at multiple buffered external pH values under otherwise comparable conditions. Define:

`pH breadth = highest pH supporting growth − lowest pH supporting growth`.

A breadth near 4–5 units qualifies, subject to the project’s numerical inclusion tolerance. “Growth supporting” should ideally be based on reproducible increases in biomass, viable counts, or growth rate—not mere post-exposure viability.

Bacteria can tolerate external pH values outside the narrower cytoplasmic range required for growth because pH sensing and homeostatic mechanisms decouple external from intracellular pH. Extreme acidophiles, for example, can grow below external pH 3 while maintaining cytoplasm near pH 6; alkaliphilic bacilli growing optimally around external pH 7.5–10.5 maintain cytoplasm around pH 7.5–8.3. These are demonstrations of homeostatic decoupling, not by themselves evidence for METPO:1000477. (krulwich2011molecularaspectsof pages 5-6, krulwich2011molecularaspectsof pages 11-12, krulwich2011molecularaspectsof pages 12-14)

### Boundary cases to exclude or annotate separately

1. **Optimum or preferred pH:** a single pH coordinate has no breadth information.
2. **Realized environmental niche:** field abundance reflects pH plus competition, dispersal, nutrients, and other covariates. Ramoneda et al. explicitly define preference as the pH of maximal relative abundance in nature, not a fundamental growth niche. (ramoneda2023buildingagenomebased pages 1-2)
3. **Acid resistance or alkaline resistance alone:** survival at pH 2 or pH 11 for one hour is not sustained growth across a 4–5-unit interval.
4. **Acid adaptation:** preconditioning can increase subsequent survival without widening the growth interval.
5. **Intracellular-pH span:** the trait concerns external assay pH, not variation in pHᵢ.
6. **Unbuffered cultures:** metabolism can shift medium pH, making nominal starting pH unreliable.
7. **Sparse pH testing:** endpoints inferred from intervals of 1–2 pH units should be marked approximate or censored.
8. **Conditional breadth:** medium composition, carbon source, sodium/potassium, oxygen, temperature, inoculum history, and buffering system should be retained as assay context.

## 2. Candidate nodes grouped by type

### Trait, environment, and assay nodes

- **pH delta mid3 — METPO:1000477**
- External pH; lower growth-supporting pH boundary; upper growth-supporting pH boundary — label-only
- Buffered pH-gradient growth assay — label-only
- Cytoplasmic pH regulation — **GO:0006885**
- Cellular response to pH — **GO:0043462**
- Cytoplasmic pH / proton-motive force / membrane potential — retain label-only unless the local ontology policy supplies reviewed terms

### Transport and bioenergetic modules

- Proton-transporting two-sector ATPase complex — **GO:0042777**
- Proton transmembrane transporter activity — **GO:0015078**
- Sodium:proton antiporter activity — **GO:0015385**
- NhaA Na⁺/H⁺ antiporter — label-only until organism and gene product are specified
- MrpABCDEFG multisubunit Na⁺/H⁺ antiporter — label-only
- K⁺/H⁺ antiporter — label-only
- UreI urea channel — taxon-specific, label-only
- Glutamate/GABA antiporter — label-only

### Enzymes, pathways, and regulatory systems

Showing the first 60 of 236 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.

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 wide pH-homeostasis flexibility to the wide-breadth pH-delta-mid3 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 7 evidence-backed generic edges (12 new nodes) from the deep-research report.

  5. · GROUND_CAUSAL_PREDICATES · claude

    Grounded 3 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (RO:0002326×2, METPO:2000017×1).

  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. · MIGRATE_MICROBE_DOMAIN_EDGES_PART2 · claude

    Re-grounded 1 causal edge(s) off microbe-domain METPO predicates onto their causal-graph counterparts (1 to reduces), issue 301 part 2. 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. Each replacement is a 1:1 mirror of its source predicate that changes only the domain, so the claim each edge makes is unchanged and directions are unchanged. The replacements are proposed in proposals/metpo_traitmech_v9 and are placeholder ids until METPO mints them.

  8. · REGROUND_CAUSAL_EDGE · claude

    Relabelled 1 causal edge from `reduces` to `decreases` and re-grounded it from METPO:2007802 to RO:0002212 (negatively regulates), issue 330. The corpus wrote two senses under the single label `reduces` - genuine electron donation, and a lessens/decreases sense - and METPO:2007802 is defined as donating electrons to the object and lowering its oxidation state, which this edge does not assert. The two senses could not be separated mechanically because the label was identical, so they migrated together in issue 329 and were split here by reading each edge. RO:0002212 declares no rdfs:domain or rdfs:range, so this introduces no entailment of the kind issue 301 removed.

  9. · NORMALISE_NODE_TYPE · claude

    Normalised causal-node type(s) so one node_id means one thing corpus-wide (issue 356): proton_motive_force: BIOLOGICAL_PROCESS -> STATE. The schema's OWN example of STATE: 'a bioenergetic or molecular state of the cell (e.g. proton motive force ...) ... the state is the gradient / steady-value, not its establishment'. All 35 occurrences describe the gradient -- every description across all four types reads 'electrochemical proton gradient', including the 13 typed BIOLOGICAL_PROCESS ('Transmembrane electrochemical gradient generated by respiration'), which name the gradient and its provenance rather than the generating process. Nothing here means the establishment, so this is a retype and not a rename; records that DO mean the process already use a separate id (proton_motive_force_generation in ph_delta.yaml). Also settles the one edge #356 was filed for: phototrophic.yaml's CAPACITY typing was blocking `powers` (METPO:2007900), which is gated to BIOLOGICAL_PROCESS|STATE.

  10. · NORMALISE_NODE_TYPE · claude

    Under the PATHWAY-vs-BIOLOGICAL_PROCESS rule, one node_id means one thing corpus-wide (issue 356): aa_decarboxylation is typed BIOLOGICAL_PROCESS. PATHWAY is a named, conventionally enumerable multi-step route; BIOLOGICAL_PROCESS is everything else. The same concept as amino_acid_decarboxylation under a shorter id, with a BYTE-IDENTICAL label ('amino-acid decarboxylation pathways') and a reaction-class description ('Decarboxylation pathways that consume protons and store energy as PMF'). Caught in review (#394): both this table and INCONSISTENT_NODE_TYPE key on node_id, so retyping the long-named one would have created a fresh split between two ids nothing compares. Included here rather than left, because this tranche is what would have caused it.

  11. · GROUND_CAUSAL_NODES · claude

    Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv (METPO:1007500×1).

  12. · NORMALISE_NODE_TYPE · codex

    Tranche 5 of issue 356 settles the process/quality families and merges ids that meant the same sense: phosphate_buffering is BIOLOGICAL_PROCESS, proton_permeability is QUALITY. Both occurrences describe cytoplasmic phosphate pools buffering protons and stabilizing pH: the buffering action, not the size of a buffer reservoir. The distinct cytoplasmic_buffering_capacity id remains CAPACITY for that quantity sense. Proton permeability is a measurable membrane property, which is the schema's QUALITY sense rather than a biological process.

  13. · 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 ph_delta_mid3_wide_breadth=NONMECHANISTIC with scope_notes; marked 2 GENE_OR_PROTEIN node(s) REVIEWED_LABEL_ONLY with grounding_notes (proton_pumping_respiratory_complexes, f0f1_atpase).

  14. · ADD_CANONICAL_EXAMPLES · codex

    Resolved issue #444 after the #591 source/bin policy with 1 direct source-backed canonical example(s): Gemmobacter lutimaris (NCBITaxon:2306023; DOI:10.1099/ijsem.0.003375). The note retains the measured value or scopes broad-class examples to the cited branch; no paid research was used.

  15. · REVIEW_CAUSAL_EVIDENCE · codex

    Reviewed the wide ph_delta_mid3_wide_breadth graph for issue #183: added snippets to 8 edge-level evidence items and grounded 4 unmapped pH-homeostasis predicates to RO:0002211, RO:0002326, or biolink:produces. No paid research service was called.

  16. · CONNECT_CAUSAL_GRAPH_COMPONENTS · codex

    Resolved issue #183 graph fragmentation (6 components to 1) by adding 5 source- and verbatim-snippet-backed association connectors among the PMF generation, PMF regulation, alkaline Na+/H+ antiport, ATPase, phosphate-buffering, amino-acid decarboxylation, and membrane proton-permeability branches. No paid research service was called.

  17. · ADVERSARIAL_REVIEW_REPAIR · codex

    Addressed PR #664 adversarial review: replaced the weak Poolman section-heading snippets with exact text supporting F0F1-ATPase pH-homeostasis and decarboxylation-driven PMF edges.

  18. · ADVERSARIAL_REVIEW_REPAIR · codex

    Addressed PR #664 adversarial review issue #683: normalized the Poolman F0F1-ATPase evidence snippet by removing MathML brace markup so the snippet matches the source text.

  19. · ADVERSARIAL_REVIEW_REPAIR · codex

    Addressed PR #664 adversarial review issue #685: replaced weak pH edge snippets with exact source spans that carry their edge claims, and left derived pH-axis bin membership in notes instead of fragment snippets.

  20. · ADVERSARIAL_REVIEW_REPAIR · codex

    Addressed PR #664 adversarial review issues #688 and #690: restored a supporting Krulwich snippet on the pH-delta bin membership edge and requoted the Poolman phosphate-buffering edge from the primary source text.

  21. · ADVERSARIAL_REVIEW_REPAIR · codex

    Addressed PR #664 adversarial review issues #696, #698, and #699: requoted weak Krulwich pH-homeostasis edge snippets and removed unsupported pH-breadth hub connectors that only joined generic review branches to quantitative bin nodes.

  22. · ADVERSARIAL_REVIEW_REPAIR · codex

    Addressed PR #664 adversarial review issue #702: appended corrective issue-183 provenance after evidence-weak connectors were pruned; this NONMECHANISTIC graph intentionally ships with 6 disconnected components until independent trait-specific connectors are curated.