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psychrotolerant

METPO:1000618 · CLASS · REVIEWED

A temperature preference in which growth can occur at low temperatures without an obligate low-temperature preference.

Psychrotolerant facultative cold-adaptation mechanism

DOI-backed graph linking psychrotolerance to low-temperature membrane and enzyme acclimation that does not preclude growth at moderate ambient temperatures.

Psychrotolerant facultative cold-adaptation mechanism Interactive directed graph showing evidence-backed causal relationships for psychrotolerant.

Edge evidence

  • low temperature decreases membrane fluidity RO:0002212

    Low temperature reduces membrane fluidity, requiring compensation.

    • DOI:10.1038/sj.embor.7400662 decreased membrane fluidity Supports cold-end membrane stress as the physical challenge for psychrotolerant growth.
  • facultative lipid remodeling regulates membrane fluidity RO:0002211

    Facultative lipid remodeling maintains workable membrane fluidity at low temperature.

    • DOI:10.1146/annurev-micro-091313-103612 more unsaturated fatty acids Supports homoviscous adaptation as the mechanism employed under cold exposure.
  • cold-shock response confers psychrotolerant METPO:2007700

    The cold-shock response enables acclimation to low temperature without obligate cold dedication.

    • DOI:10.1038/sj.embor.7400662 Cold-shock proteins have also been described Supports cold-shock proteins as a hallmark facultative-cold adaptation.
  • facultative lipid remodeling manifests as psychrotolerant METPO:2007400

    Facultative lipid remodeling at low temperature manifests the psychrotolerant trait in representative organisms.

    • DOI:10.1099/ijs.0.65141-0 Pseudomonas guineae sp. nov., a novel psychrotolerant bacterium Supports the trait endpoint in a representative organism.
  • low temperature causes membrane rigidification and thickening biolink:causes

    A low-temperature shift causes membrane rigidification and thickening toward a gel-phase transition.

    • DOI:10.1128/spectrum.03925-23 Cold shock causes membrane rigidification and concomitant thickening, potentially culminating in a gel-phase transition.
  • low temperature increases unsaturated hopanoids RO:0002213

    Decreasing growth temperature increases the unsaturated hopanoid fraction as a compositional cold adaptation.

    • DOI:10.1007/s42770-023-01057-4 As the growth temperature decreased from 20 to 4 C, the total percent of unsaturated hopanoids increased from 27 to 49%.
  • compatible solute accumulation protects protein and membrane stability under cold stress

    Compatible solute accumulation stabilizes proteins and membranes during low-temperature stress.

    • DOI:10.37256/amtt.5220244537 Compatible solutes depress freezing point, stabilize proteins and membranes, scavenge radicals, and act as cryoprotectants.
  • extracellular polymeric substances (EPS) provides cryoprotection against freeze-thaw cycles

    EPS surrounding cells provide cryoprotection against freeze-thaw cycles.

    • DOI:10.37256/amtt.5220244537 EPS surrounding cells play a critical role in cold adaptation by providing protection against freeze-thaw cycles and acting as cryoprotectants.

Provenance

Source
METPO (2025-11-25)
Definition source
DOI:10.1099/ijs.0.65141-0

Parent traits (1)

kg-microbe context

Matched 1 kg-microbe node via direct_metpo.

  • METPO:1000618 [-0.575, -4.190, -4.805, +2.930, …]

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/psychrotolerant-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: psychrotolerant

## 1. Trait scope

**Trait:** **psychrotolerant**  
**Identifier:** **METPO:1000618**  
**Category/kind:** ENVIRONMENT / CLASS  
**Parent:** METPO:1000613  
**Reviewed definition:** “A temperature preference in which growth can occur at low temperatures without an obligate low-temperature preference.”

### Operational interpretation

For TraitMech, psychrotolerance should mean **demonstrated multiplication at low temperature combined with an optimum or substantial growth capacity at warmer temperature**. A useful contemporary operational definition is growth at approximately **4°C with an optimum above 20°C**. Examples include *Pseudomonas* spp., *Listeria monocytogenes*, *Yersinia enterocolitica*, and *Aeromonas hydrophila* (ramon2023ageneraloverview pages 1-2).

This is a facultative thermal phenotype, not merely residence in a cold habitat. The phenotype should normally be supported by growth curves, colony formation, biomass increase, or another multiplication assay at both low and non-low temperatures.

### Boundaries

- **Psychrophile:** low-temperature growth is optimal or effectively obligate; obligate psychrophiles commonly have upper growth limits around 10–20°C. By contrast, psychrotolerant organisms retain a broader, warmer growth range (moyer2017psychrophilesandpsychrotrophs pages 2-3).
- **Cold-shock tolerant:** survival after an abrupt downshift does not establish sustained low-temperature growth.
- **Freeze–thaw resistant:** viability after freezing and thawing is not equivalent to multiplication at low temperature.
- **Cryotolerant/dormant:** persistence or metabolic signatures below 0°C do not by themselves demonstrate growth.
- **Cold-adapted enzyme:** activity of an isolated enzyme at low temperature does not establish organism-level psychrotolerance.
- **Genomic prediction:** possession or induction of desaturases, cold-shock proteins, helicases, compatible-solute systems, or antifreeze proteins is mechanistic support, not sufficient phenotype evidence.

The distinction is assay-sensitive. Medium, salinity, oxygenation, inoculum history, duration, and the selected “low” temperature can change the classification. The literature also uses *psychrotroph*, *psychrotolerant*, and *facultative psychrophile* inconsistently; therefore, measured cardinal growth temperatures should be retained whenever available.

## 2. Current mechanistic model

The most defensible causal architecture is modular rather than a single universal pathway:

1. **Low temperature reduces molecular motion** and pushes membrane phospholipids from a liquid-crystalline state toward a gel state.
2. **Membrane rigidification is sensed**, in some taxa through membrane-associated two-component systems.
3. **Lipid remodeling** increases low-melting-point acyl chains—cis-unsaturated, polyunsaturated, short-chain, or appropriate branched-chain fatty acids—restoring membrane fluidity and transport/respiratory function.
4. Cold stabilizes RNA secondary structures and impairs transcription, translation, ribosome maturation, and protein folding.
5. **Cold-shock RNA chaperones, DEAD-box helicases, RNases, ribosome-biogenesis factors, and molecular chaperones** preserve gene expression.
6. Compatible solutes, extracellular polymers, and ice-binding proteins can stabilize proteins and membranes or alter extracellular freezing behavior.
7. Catalase, superoxide dismutase, and related systems mitigate cold-associated oxidative stress.
8. The combined effects enable sustained low-temperature metabolism and growth while preserving growth at warmer temperatures.

A 2023 authoritative review emphasizes that cooling changes membranes from liquid-crystalline to gel phase and identifies the response as homeoviscous adaptation. It lists increased unsaturation, shorter chains, branched chains, hopanoid remodeling, glycolipids, and pigments as alternative solutions rather than a universal signature (ramon2023ageneraloverview pages 2-4).

## 3. Candidate nodes grouped by type

### Trait and environmental nodes

- psychrotolerant — **METPO:1000618**
- low-temperature growth — label-only phenotype node
- low temperature / temperature downshift — label-only experimental factor
- refrigeration temperature — label-only application-specific condition
- extracellular water — **CHEBI:15377**
- freeze–thaw exposure — label-only; should not be conflated with the target

### Cellular structures and physical states

- cytoplasmic membrane — use a taxon-appropriate GO cellular-component term after organismal context is fixed
- liquid-crystalline membrane state — label-only
- gel-state/rigidified membrane — label-only
- membrane fluidity — label-only quantitative property
- cell wall — **GO:0005618**, where taxonomically applicable

Showing the first 60 of 260 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_WITH_ORGANISM_EXAMPLE · codex

    Added Pseudomonas guineae organism example with PMID-backed evidence.

  3. · CURATED_CAUSAL_GRAPH · claude

    Added DOI-backed causal graph linking facultative cold adaptation (lipid remodeling and cold-shock response) to the psychrotolerant trait.

  4. · IMPROVED_CAUSAL_GRAPH_EVIDENCE · codex

    Replaced Pseudomonas guineae PMID fallback with the article DOI in definition, record evidence, and CausalEdge evidence.

  5. · GROUND_CAUSAL_PREDICATES · claude

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

  6. · GROUND_CAUSAL_PREDICATES · claude

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

  7. · RENAME_PREDICATE_LABELS · claude

    Renamed 1 causal-edge predicate label(s) to align with existing groundings: maintains → regulates ×1.

  8. · GROUND_CAUSAL_PREDICATES · claude

    Grounded 1 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (RO:0002211×1).

  9. · GROUND_CAUSAL_NODES · claude

    Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv (PATO:0000383×1).

  10. · GROUND_CAUSAL_NODES · claude

    Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv (METPO:1007505×1).

  11. · RETYPE_CAUSAL_NODES · claude

    Re-typed 1 causal-node node_type field(s) to align with CausalNodeTypeEnum semantics: membrane fluidity: BIOLOGICAL_PROCESS → QUALITY ×1.

  12. · GROUND_CAUSAL_PREDICATES · claude

    Grounded 1 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (RO:0002212×1).

  13. · FIX_NODE_GROUNDING_CURIE · claude

    Overwrote 1 causal-node grounding(s) to corrected CURIEs (phase-2 id-label fix; verified vs OAK).

  14. · REMOVE_REDUNDANT_SYNONYM · claude

    Removed 1 synonym(s) whose text duplicated the label (seeder redundancy; no information lost).

  15. · ENRICH_CAUSAL_GRAPH · claude

    Added 5 evidence-backed generic edges (7 new nodes) from the deep-research report.

  16. · GROUND_CAUSAL_PREDICATES · claude

    Grounded 2 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (biolink:causes×1, RO:0002213×1).

  17. · MIGRATE_ENABLES_TRAIT_EDGES · claude

    Migrated 1 causal edge(s) off enables/RO:0002327 with a TRAIT object (1 to confers), issue 302. RO:0002327 has range 'biological process or activity', which a trait (a disposition) cannot satisfy, so the previous form entailed trait is-a BiologicalProcessOrActivity. The replacements are proposed in proposals/metpo_traitmech_v8 and are placeholder ids until METPO mints them.

  18. · DROP_CAUSAL_NODE · claude

    Dropped node growth_at_4c and its edges. Issue 352. 'Ability to grow at refrigeration-range low temperature (4 C)' IS METPO:1000618 (psychrotolerant), the record's own term and the grounding of psychrotolerant_trait, which is the node it hangs off. A leaf restating its own parent. The parent keeps two other in-edges (cold_shock_response confers, facultative_lipid_remodeling manifests as), so nothing is stranded.