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temperature optimum very low

METPO:1000441 · CLASS · REVIEWED

A temperature optimum phenotype with the best-growth ambient temperature at or below approximately 10 °C, characteristic of psychrophilic physiology.

Trait evidence (1)

  • DOI:10.1038/sj.embor.7400662
    growing well at temperatures around the freezing point of water

    Psychrophile review supports growth at very low temperatures as the psychrophilic optimum.

Temperature-optimum-very-low psychrophile context

DOI-backed nonmechanistic graph connecting cold-adapted membranes, cold-shock RNA chaperones, compatible-solute cryoprotection, antifreeze-protein ice binding, and flexible enzyme branches to the at-or-below-10-degrees-C optimum 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.

Temperature-optimum-very-low psychrophile context Interactive directed graph showing evidence-backed causal relationships for temperature optimum very low.

Edge evidence

  • cold environment selects for psychrophile cold-adapted machinery METPO:2007401

    Cold environments select for cold-adapted enzymes and lipids.

    • DOI:10.1038/sj.embor.7400662 growing well at temperatures around the freezing point of water Supports cold habitats as the context for psychrophile machinery.
  • psychrophile cold-adapted machinery confers temperature optimum very low METPO:2007700

    Psychrophile cold-adapted machinery yields a very-low temperature optimum.

  • temperature optimum very low is a temperature optimum rdfs:subClassOf

    Temperature optimum very low is a quantitative bin of the temperature-optimum phenotype.

    • DOI:10.1038/sj.embor.7400662 growing well at temperatures around the freezing point of water Supports a ≤10 °C optimum as a value within the temperature-optimum distribution.
  • fatty acid desaturase activity increases unsaturated fatty acids RO:0002213

    Fatty acid desaturase activity increases unsaturated acyl chains.

    • DOI:10.17159/sajs.2018/20170254 increase in the proportion of unsaturated acyl chains Verified against the open Hamdan review; lower growth temperatures are described as activating desaturases that convert saturated acyl fatty acids to unsaturated ones.
  • unsaturated fatty acids contributes to membrane fluidity at low temperature RO:0002326

    Increased unsaturated fatty acids contribute to membrane fluidity at low temperature.

    • DOI:10.1128/AEM.01928-22 proportion of unsaturated fatty acids was higher Verified against the open Yang et al. abstract; Bacillus simplex H-b cultured at low temperature carried a higher unsaturated-fatty-acid proportion.
    • DOI:10.17159/sajs.2018/20170254 maintain optimum membrane fluidity Verified against the open Hamdan review; fatty-acyl-chain modifications are described as preserving membrane fluidity in freezing environments.
  • cold shock proteins / RNA chaperones contributes to translation at low temperature RO:0002326

    Cold shock proteins / RNA chaperones contribute to transcription and translation in the cold.

    • DOI:10.17159/sajs.2018/20170254 regulation of cellular protein synthesis Verified against the open Hamdan review; cold-shock proteins are linked to cellular protein-synthesis regulation, including transcription and translation initiation.
  • trehalose contributes to cryoprotection RO:0002326

    Trehalose contributes to cryoprotection.

    • DOI:10.17159/sajs.2018/20170254 preventing protein denaturation and aggregation Verified against the open Hamdan review; trehalose is reported as preventing protein denaturation and aggregation in psychrophilic bacteria.
  • antifreeze / ice-binding proteins causes thermal hysteresis / lowered freezing point biolink:causes

    Antifreeze proteins lower the freezing point via thermal hysteresis.

    • DOI:10.1007/s42770-023-01057-4 lower the water freezing point Verified against the open Ramón et al. abstract and review text; anti-freeze proteins are described as lowering the water freezing point via thermal hysteresis or ice-recrystallization inhibition.
  • increased enzyme structural flexibility increases catalytic activity at low temperature RO:0002213

    Increased enzyme structural flexibility increases catalytic activity at low temperature.

    • DOI:10.17159/sajs.2018/20170254 up to 10-fold higher specific activity Verified against the open Hamdan review; psychrophiles are described as producing structurally flexible enzymes with higher low-temperature specific activity than mesophilic homologues.
  • translation at low temperature associated with psychrophile cold-adapted machinery biolink:associated_with

    Cold-shock protein support for translation is associated with psychrophile cold-adapted machinery.

    • DOI:10.4161/rna.7.6.13482 facilitating transcription and translation at low temperature Verified against the open Phadtare and Severinov PubMed abstract; this connector keeps cold-shock RNA chaperones as protein-synthesis context for psychrophile physiology.
  • protein and membrane stabilization under cold stress associated with psychrophile cold-adapted machinery biolink:associated_with

    Compatible-solute protein and membrane stabilization is associated with psychrophile cold-adapted machinery.

    • DOI:10.17159/sajs.2018/20170254 compatible solutes such as trehalose and glycine-betaine Verified against the open Hamdan review; this connector keeps glycine-betaine compatible-solute effects as broad cold-stress context.
  • cryoprotection associated with protein and membrane stabilization under cold stress biolink:associated_with

    Trehalose-linked cryoprotection is associated with protein and membrane stabilization during cold stress.

    • DOI:10.17159/sajs.2018/20170254 counteracting protein aggregation, improving protein folding and stabilizing membranes and proteins at chilling temperatures Verified against the open Hamdan review; this connector keeps trehalose as a compatible-solute cryoprotection branch.
  • thermal hysteresis / lowered freezing point associated with cryoprotection biolink:associated_with

    Antifreeze-protein thermal hysteresis is associated with cryoprotection near freezing.

    • DOI:10.1007/s42770-023-01057-4 AFPs lower the water freezing point, avoiding frostbite due to their thermal hysteresis Verified against the open Ramón et al. abstract and review text; this connector keeps antifreeze proteins as ice-binding cryoprotection context.
  • catalytic activity at low temperature associated with psychrophile cold-adapted machinery biolink:associated_with

    Flexible-enzyme catalytic activity is associated with psychrophile cold-adapted machinery.

    • DOI:10.17159/sajs.2018/20170254 adapted to function at low temperatures, with high catalytic constants Verified against the open Hamdan review; this connector keeps low-temperature enzyme flexibility as contextual psychrophile machinery.
  • membrane fluidity at low temperature associated with psychrophile cold-adapted machinery biolink:associated_with

    Membrane-fluidity regulation is associated with psychrophile cold-adapted machinery.

    • DOI:10.17159/sajs.2018/20170254 regulate or modulate the fluidity of the membrane in freezing environments Verified against the open Hamdan review; the membrane-fluidity section names membrane-fluidity modulation in freezing environments as a frequent psychrophile cold-adaptation strategy.

Provenance

Identifier source
METPO (2026-06-12)
Definition source
DOI:10.1038/sj.embor.7400662

Parent traits (1)

Synonyms (2)

  • Psychrophile EXACT_SYNONYM · metpo.owl
  • TO_<=10 RELATED_SYNONYM · metpo.owl

kg-microbe context

Matched 1 kg-microbe node via direct_metpo.

  • METPO:1000441 [-4.303, -0.200, +0.305, +0.724, …]

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/temperature_optimum_very_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: microbial “temperature optimum very low”

**Target trait:** `METPO:1000441`
**Category / kind / status:** ENVIRONMENT / CLASS / REVIEWED
**Parent:** `METPO:1000304`
**Synonyms:** Psychrophile; TO_<=10

## 1. Scope and current interpretation

`METPO:1000441` should represent an **assay-observed temperature optimum**, namely that maximal or near-maximal microbial growth occurs at an ambient temperature **at or below approximately 10 °C**. The preferred evidence is a growth-rate or biomass-versus-temperature curve under otherwise controlled conditions, not merely isolation from a cold habitat, survival after freezing, transcriptional response to cold, or detectable growth at 4–10 °C.

This ontology class is **narrower than the conventional microbiological definition of a psychrophile**. Recent reviews commonly define psychrophiles as organisms growing at 0 °C, with optimum around or below 15 °C and maximum around or below 20 °C; psychrotrophs/psychrotolerants can grow in the cold but have optima or maxima above those thresholds. Thus an organism with optimum 13–15 °C may be a conventional psychrophile but does not necessarily satisfy the supplied `TO_<=10` threshold. Conversely, growth at −10 °C does not establish an optimum ≤10 °C unless temperatures above −10 °C were compared. (ramon2023ageneraloverview pages 1-2, bao2023miningofkey pages 1-2, moyer2017psychrophilesandpsychrotrophs pages 1-2)

**Boundary exclusions** should include:

- **Cold tolerance/psychrotolerance:** capacity to grow or persist at low temperature while having a warmer optimum.
- **Minimum growth temperature:** the lowest temperature permitting detectable growth.
- **Maximum growth temperature:** useful for conventional psychrophile classification but not equivalent to the optimum.
- **Freeze survival or metabolic activity without growth:** relevant to cryoprotection, not sufficient for this trait.
- **Transient cold-shock response:** an acclimation program that also occurs in mesophiles.
- **Cold-active purified enzyme:** a molecular property that may contribute to cold growth but does not establish the organism-level optimum.

Examples illustrate the distinction: *Planococcus halocryophilus*, *Psychromonas ingrahamii*, and *Psychrobacter arcticus* can grow at −15, −12, and −10 °C, respectively, with reported generation times of approximately 50, 10, and 39 days, but these minima alone do not specify their optimum. *Psychrobacter cryopegella* can thrive at −10 °C and remain metabolically active at −20 °C, again demonstrating extreme cold activity rather than necessarily proving `TO_<=10`. (purwar2024adaptationsofpsychrophilic pages 3-4, moyer2017psychrophilesandpsychrotrophs pages 1-2)

## 2. Mechanistic model

Current expert understanding is that very-low-temperature growth is a **multifactorial systems phenotype**, not a single-gene trait. Low temperature reduces membrane fluidity, molecular diffusion and catalytic rates; increases viscosity; stabilizes inhibitory RNA secondary structures; perturbs protein folding and ribosome assembly; promotes extracellular and intracellular ice formation; and can increase reactive-oxygen burden. Psychrophilic physiology compensates through coordinated membrane remodeling, cold-efficient catalysis, macromolecular homeostasis, cryoprotection, antioxidant defense, transport, and energy-management mechanisms. (moyer2017psychrophilesandpsychrotrophs pages 2-3, ramon2023ageneraloverview pages 1-2, purwar2024adaptationsofpsychrophilic pages 6-7, purwar2024adaptationsofpsychrophilic pages 8-10)

The strongest recent functional result in the retrieved literature is Li et al. (November 2024). Six *Rhodococcus* sp. RCBS9 proteins—small heat-shock protein, DPS, GroEL, USP-1, Cu/Zn-SOD, and USP-2—were heterologously expressed in *E. coli* BL21. At 10 °C, strains expressing DPS, GroEL, or USP-2 reached approximately OD600 1.4 after four hours, versus approximately 1.0–1.1 for vector control. This supports gene-to-low-temperature-growth edges, but only in a short-duration heterologous assay; it does not prove that any gene changes the thermal optimum or is necessary in the native strain. The authors also reported declining counts after eight hours and called for deeper validation. (li2024mechanismsunderlyingthe pages 10-12, li2024mechanismsunderlyingthe pages 12-13)

Bao et al. (July 2023) identified 124 candidate cold-adaptation genes in psychrotrophic *Pseudomonas fragi* D12, including 46 associated with membrane fluidity—four in unsaturated-fatty-acid synthesis and 42 in fatty-acid degradation—and 233 stress-response genes. Responses differed by temperature interval: 30→15 °C was associated with membrane-fluidity maintenance, extracellular polymer and compatible-solute production, and reduced ROS, whereas 15→4 °C preferentially induced chaperones and transcription factors. This is valuable mechanistic evidence but is primarily comparative-genomic/transcriptomic and comes from a psychrotroph, so it should not be asserted as a direct cause of `METPO:1000441`. (bao2023miningofkey pages 1-2, bao2023miningofkey pages 6-7)

## 3. Candidate graph nodes

### Trait and assay nodes

- **temperature optimum very low** — `METPO:1000441`
- **parent temperature-optimum phenotype** — `METPO:1000304`
- Growth rate, generation time, biomass yield, OD600, colony formation
- Controlled ambient temperature; temperature series; incubation duration
- **Cold response** — `GO:0009409`

### Environmental and physical nodes

- Low ambient temperature; subzero temperature; freeze–thaw cycle
- Extracellular ice; intracellular ice; ice recrystallization
- Increased solvent viscosity; reduced molecular kinetic energy
- Membrane liquid-crystalline state; membrane fluidity
- Cold habitats such as sea ice, permafrost, glaciers, polar soils, and deep ocean—prefer ENVO grounding only after term lookup

### Cellular structures and processes

- Membrane / membrane component — `GO:0016020`
- Transport — `GO:0006810`
- Electron-transport chain — `GO:0022900`
- Ribosome biogenesis — `GO:0042254`
- Translation — `GO:0006412`
- Protein folding — `GO:0006457`
- Chaperone-mediated protein folding — `GO:0061077`
- Catalytic activity — `GO:0003824`

Showing the first 60 of 218 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.

  • Clostridium psychrophilum NCBITaxon:132926 DOI:10.1016/j.bbalip.2013.02.004 Clostridium psychrophilum was cultured near its reported optimal growth temperature of 5 degrees C and also at -5 degrees C for the cited membrane-lipid study; the optimum is wholly inside the at-most-10-degree 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 psychrophile cold-adapted machinery to the temperature-optimum-very-low 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. · GROUND_CAUSAL_PREDICATES · claude

    Grounded 1 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (METPO:2007401×1).

  5. · GROUND_CAUSAL_NODES · claude

    Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv (ENVO:01000309×1).

  6. · ENRICH_CAUSAL_GRAPH · claude

    Added 8 evidence-backed generic edges (13 new nodes) from the deep-research report.

  7. · GROUND_CAUSAL_PREDICATES · claude

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

  8. · GROUND_CAUSAL_NODES · claude

    Grounded 2 causal-node grounding field(s) via mappings/node_grounding.tsv (CHEBI:27208×1, CHEBI:17750×1).

  9. · 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.

  10. · SPLIT_PROTEIN_FROM_ACTIVITY · claude

    Separated the protein sense from the activity sense so one node_id means one thing (issue 356): renamed fatty_acid_desaturase -> fatty_acid_desaturase_activity (MOLECULAR_FUNCTION sense). Described as 'Desaturase ACTIVITY introducing double bonds into fatty acyl chains', against 'Desaturase enzyme (e.g., Des) that introduces double bonds' for the protein occurrences. fatty_acid_desaturase_activity already exists corpus-wide as MOLECULAR_FUNCTION.

  11. · 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 temperature_optimum_very_low_psychrophile_setpoint=NONMECHANISTIC with scope_notes; marked 2 GENE_OR_PROTEIN node(s) REVIEWED_LABEL_ONLY with grounding_notes (cold_shock_proteins, antifreeze_proteins).

  12. · ADD_CANONICAL_EXAMPLES · codex

    Resolved issue #444 after the #591 source/bin policy with 1 direct source-backed canonical example(s): Clostridium psychrophilum (NCBITaxon:132926; DOI:10.1016/j.bbalip.2013.02.004). The note retains the measured value or scopes broad-class examples to the cited branch; no paid research was used.

  13. · REVIEW_CAUSAL_EVIDENCE · codex

    Reviewed the temperature_optimum_very_low_psychrophile_setpoint graph for issue #183: added snippets to 8 edge-level evidence items and grounded the desaturase, membrane-fluidity, cold-shock, glycine-betaine, and trehalose predicates to RO:0002213 or RO:0002326. No paid research service was called.

  14. · 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 cold-shock RNA support, compatible-solute cryoprotection, antifreeze protein ice-binding, and low-temperature flexible-enzyme branches. No paid research service was called.

  15. · ADVERSARIAL_REVIEW_REPAIR · codex

    Addressed PR #664 adversarial review: corrected the Phadtare and Severinov cold-shock connector note so it names the DOI-matched source instead of the Hamdan psychrophile review.

  16. · ADVERSARIAL_REVIEW_REPAIR · codex

    Addressed PR #664 adversarial review issue #700: removed the unsupported membrane-fluidity and glycine-betaine psychrophile edges, and removed the abandoned glycine-betaine node.

  17. · ADVERSARIAL_REVIEW_REPAIR · codex

    Addressed PR #664 adversarial review issue #704: restored the pre-existing membrane-fluidity branch as a DOI-backed association to psychrophile cold-adapted machinery after the final connector prune over-deleted it.