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pH delta high

METPO:1000478 · CLASS · REVIEWED

A pH delta phenotype with a growth-supporting pH breadth of approximately 5–9 pH units, characteristic of euryphilic pH-tolerance physiology.

pH-delta-high euryphilic breadth

DOI-backed graph linking maximal pH-homeostasis flexibility to a pH growth breadth of approximately 5–9 pH units.

pH-delta-high euryphilic breadth Interactive directed graph showing evidence-backed causal relationships for pH delta high.

Edge evidence

  • maximal pH-homeostasis flexibility confers pH delta high METPO:2007700

    Maximal pH-homeostasis flexibility yields an extreme pH-delta breadth.

    • DOI:10.1016/j.tim.2007.02.005 proton motive force Supports maximal pH-homeostasis flexibility as the basis of euryphilic breadth.
  • pH delta high is a pH delta rdfs:subClassOf

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

    • DOI:10.1038/nrmicro2549 pH homeostasis Supports the 5–9 unit breadth as a value within the pH-delta distribution.
  • Na+/H+ antiporters contributes to pH delta high RO:0002326

    Na+/H+ antiport is a core regulator of cytoplasmic pH across changing external pH.

    • DOI:10.1093/femsre/fuad033 Key regulators of bacterial pH homeostasis are Na+/H+ and K+/H+ antiporters.
  • respiratory proton-pumping enzymes helps maintain cytoplasmic pH homeostasis

    Electron-transport proton pumps counteract pH stress by controlling proton flux.

    • DOI:10.1093/femsre/fuad033 Proton-pumping enzymes (electron transport components) are major homeostasis regulators.
  • F0F1-ATPase contributes to pH delta high RO:0002326

    F0F1-ATPase participates in pH homeostasis via proton extrusion or uptake.

    • DOI:10.1093/femsre/fuad033 F0F1-ATPase is named among key regulators of bacterial pH homeostasis.
  • metabolite decarboxylation pathways contributes to pH delta high RO:0002326

    Proton-consuming decarboxylation pathways support broad pH tolerance.

    • DOI:10.1093/femsre/fuad033 Metabolite decarboxylation pathways are key regulators of pH homeostasis.
  • cytoplasmic buffering capacity stabilizes cytoplasmic pH homeostasis

    High buffering capacity limits pH swings, enabling broader pH tolerance.

    • DOI:10.1093/femsre/fuad033 Internal pH kept ~7.0-7.5 as buffers absorb fluctuations.
  • near-neutral cytoplasmic pH confers growth across external pH 5.5-9.0 METPO:2007700

    Neutralophiles maintain narrow internal pH while growing over a broad external range.

    • DOI:10.1038/nrmicro2549 Neutralophiles grow at external pH ~5.5-9.0 while maintaining cytoplasmic pH ~7.5-7.7.
  • constant proton motive force supports pH delta high

    A relatively constant PMF across external pH is a hallmark of broad pH tolerance.

    • DOI:10.1093/femsre/fuad033 PMF of neutralophilic bacteria kept relatively constant over pH 5 to 8.
  • membrane lipid/porin composition changes decreases inward proton leakage RO:0002212

    Membrane/porin composition changes lower proton leak during acid stress.

    • DOI:10.1038/nrmicro2549 Membrane lipid and porin composition changes minimize inward proton leakage during acid stress.

Provenance

Source
METPO (2025-11-25)
Definition source
DOI:10.1038/nrmicro2549

Parent traits (1)

Synonyms (1)

  • pHd_5_9 RELATED_SYNONYM · metpo.owl

kg-microbe context

Matched 1 kg-microbe node via direct_metpo.

  • METPO:1000478 [-0.781, -1.339, -0.603, +3.022, …]

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_high-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 **pH delta high**

## 1. Scope summary

**Target:** `METPO:1000478` (“pH delta high”; synonym `pHd_5_9`; parent `METPO:1000232`).

The safest interpretation is an **assay-observed capacity for growth across an unusually broad external-pH interval**, approximately 5–9 pH units wide, rather than a preferred pH, an endpoint tolerance, or survival after an acute pH shock. The mechanistic core is maintenance of a growth-compatible cytoplasmic pH and bioenergetic state while external proton activity changes by orders of magnitude.

The foundational synthesis reports that many neutralophilic bacteria can grow from approximately pH 5.5 to 9.0 while maintaining cytoplasmic pH around 7.5–7.7. Thus, a broad growth range is compatible with a much narrower intracellular operating range. The transmembrane pH gradient is also a component of proton motive force (PMF), linking pH homeostasis directly to ATP synthesis, respiratory energetics, solute transport, and motility (krulwich2011molecularaspectsof pages 1-3).

### Recommended operational definition

Curate the trait only when the same strain shows reproducible **net growth**—for example, increased biomass, optical density, cell counts, or colony formation—over an approximately 5–9-unit pH breadth under otherwise comparable conditions. Record:

- measured lower and upper growth limits;
- optimum pH separately;
- buffer system and buffering capacity;
- temperature, salinity, oxygen regime, medium, carbon source, and incubation time;
- whether pH remained controlled or drifted during growth;
- whether endpoints denote growth, lag extension, maintenance, or survival.

### Boundary cases

1. **Acid resistance is not broad pH growth.** *E. coli* may survive pH 2–2.5 for hours through amino-acid-dependent resistance systems, but this is explicitly survival without growth and should not by itself instantiate `METPO:1000478` (li2024responseofescherichia pages 1-2, li2024responseofescherichia pages 2-4).
2. **Acidophily or alkaliphily is not necessarily euryphily.** Growth at pH <3 or >11 may reflect specialization at one endpoint. For example, alkaliphilic *Bacillus pseudofirmus* OF4 has specialized antiporters and ATP-synthase adaptations; these mechanisms are informative components but do not establish symmetric broad-range growth (krulwich2011molecularaspectsof pages 12-14).
3. **Optimum is not breadth.** “Optimum pH 7–8” supplies no lower or upper growth boundary.
4. **Environmental recovery is not phenotype proof.** Isolation from acidic or alkaline material does not establish axenic broad-pH growth; community buffering and microhabitats can explain persistence.
5. **Acclimation, tolerance, and growth should remain distinct.** Proteomic induction at a test pH, viability after shock, and sustained cell division are different observations.

## 2. Current mechanistic model

No single universal “euryphily gene” is established. The best-supported model is a **two-sided, conditionally regulated homeostasis network**:

- At low external pH, cells limit proton entry, export protons, consume cytoplasmic protons metabolically, protect envelope and macromolecules, and repair damage.
- At high external pH, cells capture/import scarce protons, frequently through Na+/H+ or K+/H+ antiport and ATP-synthase-associated proton influx, while adjusting metabolism and surface chemistry.
- Across both sides, ion homeostasis, PMF partitioning between ΔpH and membrane potential, envelope permeability, metabolic flexibility, and pH-responsive regulation sustain a narrow intracellular pH.

The strongest direct trait-level fact is therefore:

> Broad external-pH growth **requires maintenance of a comparatively narrow, growth-compatible cytoplasmic pH**, but the particular modules implementing that requirement are taxon- and condition-dependent (krulwich2011molecularaspectsof pages 1-3).

## 3. Candidate nodes grouped by type

### A. Trait and environmental/experimental nodes

- **pH delta high** — `METPO:1000478`
- external pH; acidic external pH; alkaline external pH — label-only unless the project has established ENVO/METPO terms
- growth-supporting pH breadth — label-only assay node
- acute acid shift; acute alkaline shift — label-only experimental perturbations
- buffer identity/capacity; Na+ concentration; K+ concentration; osmolarity; salinity; oxygen availability; carbon source — essential contextual nodes
- proton — `CHEBI:24636`
- sodium cation — `CHEBI:29101`
- potassium cation — `CHEBI:29103`
- ammonium — `CHEBI:28938`
- carbon dioxide — `CHEBI:16526`
- hydrogencarbonate/bicarbonate — `CHEBI:17544`
- L-glutamate — `CHEBI:29985`
- 4-aminobutanoate/GABA — `CHEBI:16865`

### B. Biological-process and bioenergetic nodes

Showing the first 60 of 265 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 maximal pH-homeostasis flexibility to the euryphilic pH-delta-high 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 8 evidence-backed generic edges (11 new nodes) from the deep-research report.

  5. · GROUND_CAUSAL_PREDICATES · claude

    Grounded 5 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (RO:0002326×3, RO:0002327×1, METPO:2000017×1).

  6. · GROUND_CAUSAL_NODES · claude

    Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv (GO:0051453×1).

  7. · 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.

  8. · 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.

  9. · 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.

  10. · RETYPE_CAUSAL_NODE · claude

    Retyped the object node from STATE/CAPACITY to TRAIT and re-grounded its in-edge from enables/RO:0002327 to METPO:2007700 (confers), issue 334. biolink declares enables range 'biological process or activity', which only BIOLOGICAL_PROCESS, PATHWAY and MOLECULAR_FUNCTION satisfy. The node's own description gives it away as a disposition rather than a state - phrasings like "Capacity of an organism to grow and survive under...", "Ability to grow when..." and "tolerance of..." describe what an organism CAN do, which is what a TRAIT is. So the defect was the node type, not the predicate, which is the third time in this issue's neighbourhood that has been true (compare issue 331's acetate kinase step and issue 330's negated node name). With the object correctly a TRAIT, confers applies unchanged.

  11. · GROUND_CAUSAL_NODES · claude

    Grounded the retyped TRAIT node, issue 334 review. docs/CURATION_PLAYBOOK.md requires every TRAIT row to carry a grounding, and 462 of 482 TRAIT nodes in the corpus do, so leaving a newly retyped one ungrounded was the exception rather than the norm. It also mattered more than hygiene: an ungrounded TRAIT node still counts as a reachability anchor for audit-graphs, so it made UNREACHABLE_FROM_TRAIT fall on this graph without any edge changing -- the island is unchanged and FRAGMENTED_GRAPH still reports it. Grounding it makes the duplication legible instead of leaving two unrelated-looking anchors. growth_external_ph_5_5_9 is the same concept as this record's own ph_delta_high_trait, so it takes the same METPO:1000478; merging the two nodes is tracked in issue 352.

  12. · REGROUND_CAUSAL_NODE · claude

    Regrounded node growth_external_ph_5_5_9 from METPO:1000478 to METPO:1000332. Issue 352. Shared METPO:1000478 with ph_delta_high_trait, but the two say different things: this node is an ABSOLUTE external range ('~5.5-9.0'), while ph_delta_high_trait is a BREADTH ('approximately 5-9 pH units'), which is what a pH DELTA is. 1000478 belongs to the delta; this is a pH range (METPO:1000332).