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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.

pH-delta-mid3 wide-breadth pH homeostasis

DOI-backed graph linking wide pH-homeostasis flexibility to a pH growth breadth of approximately 4–5 pH units.

pH-delta-mid3 wide-breadth pH homeostasis 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.

    • DOI:10.1038/nrmicro2549 pH homeostasis Supports wide pH-homeostasis flexibility as the basis of a wide 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 external pH Supports the 4–5 unit breadth as a value within the pH-delta distribution.
  • external alkaline pH increases reliance on electrogenic Na+/H+ antiport

    High external pH increases reliance on electrogenic Na+/H+ antiport for cytoplasmic pH homeostasis.

    • DOI:10.1038/nrmicro2549 Multiple Na+/H+ and K+/H+ antiporters are critical for alkaline homeostasis, driven by membrane potential.
  • regulation of membrane potential and pH gradient supports cytoplasmic pH maintenance

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

    • DOI:10.1038/nrmicro2549 PMF (Delta-pH and Delta-psi) is central to pH homeostasis; neutralophiles keep cytoplasmic pH near 7.5 across external pH ~5.5-9.0.
  • proton-pumping respiratory complexes contribute to proton motive force

    Proton-pumping respiratory complexes contribute to the PMF used for pH homeostasis.

    • DOI:10.1038/nrmicro2549 Cells use primary proton pumps including respiratory-chain pumps to create PMF for transport and pH regulation.
  • F0F1-ATPase contributes to cytoplasmic pH maintenance RO:0002326

    F0F1-ATPase can extrude protons and contributes to pH homeostasis under acid stress.

    • DOI:10.1093/femsre/fuad033 F1Fo-ATPase hydrolytic activity can drive H+ extrusion; key regulator in low-pH contexts.
  • cytoplasmic phosphate buffering capacity stabilizes intracellular pH stability

    Cytoplasmic phosphate buffering capacity stabilizes intracellular pH.

    • DOI:10.1093/femsre/fuad033 At pH ~7.2 only ~10 free protons present; cytoplasmic phosphate buffering (~100 mM) makes buffering essential.
  • 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 Decarboxylation releases ~20 kJ/mol that can be stored as PMF; decarboxylation pathways are key pH regulators.
  • membrane lipid composition shifts decreases membrane proton permeability RO:0002212

    Membrane lipid composition shifts reduce proton permeability.

    • DOI:10.3389/fmicb.2022.1034164 Membrane composition adjustments limit proton permeability and alter phospholipid headgroups under high pH.

Provenance

Source
METPO (2025-11-25)
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.

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.