temperature range very low

Deep research

Generated by just research-trait; source: research/traits/environment/temperature_range_very_low-deep-research-falcon.md

# Curation report: microbial very-low-temperature growth

## Trait record and scope

- **Trait:** temperature range very low
- **Identifier:** **`METPO:1000448`**
- **Category / kind / status:** ENVIRONMENT / CLASS / REVIEWED
- **Parent:** `METPO:1000306`
- **Operational interpretation:** a growth-temperature-range phenotype in which **reproducible population growth extends to ≤10 °C**. The decisive observation should be biomass, viable-cell number, growth rate, or repeated division—not respiration alone, survival after cold shock, or activity of an isolated enzyme.

This operational scope is broader than the classical definition of an obligate or strict psychrophile. Traditional definitions generally require growth near 0 °C, an optimum around or below 15 °C, and an upper limit near 20 °C; psychrotrophs/psychrotolerant organisms also grow in the cold but have substantially higher optima or maxima. Recent reviews continue to use somewhat inconsistent numerical boundaries, making the measured growth range more reliable than the label “psychrophile.” (moyer2017psychrophilesandpsychrotrophs pages 2-3, purwar2024adaptationsofpsychrophilic pages 1-3, ramon2023ageneraloverview pages 1-2)

### Boundary cases

1. **Include:** sustained growth at 10, 4, 0, or subzero temperature, even where the organism's optimum is above 15 °C. Pseudoalteromonas sp. WY3, for example, grew at 4 °C but had predicted `Topt = 24.8 °C`; it therefore supports `METPO:1000448` under the supplied range definition but is not a classical strict psychrophile. Its measured rates were 0.0011, 0.0021, 0.0449, 0.1428, and 0.1478 h⁻¹ at 4, 8, 12, 16, and 25 °C, respectively; predicted `Tmin`, `Topt`, and `Tmax` were −1.2, 24.8, and 36.5 °C. (wang2024genomicinsightsinto pages 11-12)
2. **Exclude:** survival at −30 °C without demonstrated division; metabolic activity inferred at −40 °C; a transient cold-shock response followed by no growth; or an isolated cold-active enzyme. Reviews explicitly distinguish verified growth down to approximately −15 °C from survival or predicted metabolism at lower temperatures. (moyer2017psychrophilesandpsychrotrophs pages 2-3)
3. **Do not infer from habitat:** isolation from glacier, permafrost, Antarctic soil, refrigerated food, or deep ocean is insufficient without a growth assay.
4. **Do not infer strict psychrophily from ≤10 °C growth alone:** record optimum and maximum temperatures separately where available. Pseudarthrobacter psychrotolerans YJ56 grew best at 13 °C and failed to grow at 30 °C, which is much stronger evidence of a genuinely cold-adapted range than growth at 4 °C alone. (son2023morphologicalandphysiological pages 1-2)
5. **Separate acute and acclimated states:** cold shock, acclimation, and steady-state cold growth can activate different systems. A 2023 study deliberately compared sustained growth at 0 and 15 °C rather than an acute shock and found extensive transcriptional remodeling despite a comparatively stable central metabolome. (riccardi2023metabolicrobustnessto pages 1-2)

## Current mechanistic model

Very-low-temperature growth is a systems phenotype rather than a single pathway. Cooling rigidifies membranes, stabilizes inhibitory RNA structures, slows enzyme catalysis and macromolecular turnover, perturbs protein folding, raises oxidative stress through greater oxygen solubility, and can impose freeze-concentration/osmotic stress. Successful organisms combine homeoviscous membrane remodeling, RNA and ribosome maintenance, protein-quality control, cold-active catalysis, redox protection, compatible-solute/EPS production, and regulatory or metabolic buffering. Recent authoritative analysis emphasizes that the exact combination is strongly taxon- and temperature-transition-specific. (bao2023miningofkey pages 1-2, ramon2023ageneraloverview pages 1-2, riccardi2023metabolicrobustnessto pages 1-2)

## Candidate nodes grouped by type

### Phenotype, environment, and assay nodes

- `METPO:1000448` — temperature range very low.
- Low growth temperature: **10, 4, 0, or subzero °C**; retain the exact assay temperature as evidence metadata.
- Sustained low-temperature population growth; growth rate; lag duration; biomass/OD; viable count.
- Cold shock, cold acclimation, and steady-state cold growth as separate experimental-condition nodes.
- Freeze–thaw exposure and extracellular ice as separate stressors, not synonyms of low-temperature growth.
- Candidate environments: glacier ice, permafrost, Antarctic marine water, Antarctic soil, and refrigerated environments. Assign ENVO CURIEs only after checking the exact sampled habitat.

### Cellular structures and processes

- Cell membrane / plasma membrane — **GO:0005886**.
- Membrane lipid remodeling and homeoviscous adaptation — label-only pending exact ontology review.
- Membrane fluidity, permeability, and transport competence.
- Ribosome — **GO:0005840**; 50S ribosomal subunit — **GO:0005842**.
- Translation — **GO:0006412**; protein folding — **GO:0006457**.
- RNA secondary-structure remodeling / RNA helicase activity.
- Cell wall remodeling; peptidoglycan turnover.
- Oxidative-stress response — **GO:0006979**.
- Biofilm formation — **GO:0042710**.
- Central-carbon metabolic homeostasis and transcriptomic buffering.

### Genes, proteins, enzymes, and complexes

**Higher-priority, functionally supported candidates**

- **csdA**: cold-associated DEAD-box RNA helicase; knockout reduces low-temperature growth in Psychrobacter arcticus 273-4.
- **relA**: stringent-response enzyme; knockout reduces low-temperature growth in the same strain.
- **dac2**: cold-upregulated DD-peptidase/carboxypeptidase; knockout reduces low-temperature growth.
- **GroEL**: chaperonin; heterologous expression of the Rhodococcus sp. RCBS9 protein improved E. coli growth at 10 °C.
- **Dps**: DNA-binding ferritin-like stress protein; RCBS9 Dps expression improved E. coli growth at 10 °C.
- **USP-2**: universal stress protein; RCBS9 USP-2 expression improved E. coli growth at 10 °C.

**Mechanistically plausible but mostly expression/genomic-association candidates**

Showing the first 60 of 217 lines of findings; the linked file also carries the run's front matter and the prompt it was given — read the full report.