temperature optimum high

METPO:1000447 · CLASS · REVIEWED

A temperature optimum phenotype with the best-growth ambient temperature above approximately 40 °C, characteristic of thermophilic physiology.

Trait evidence (2)

DOI:10.1016/s0300-9629(97)00003-0
adapted to environments of high temperature

Thermophile-adaptation review supports the >40 °C optimum as the thermophile category.
DOI:10.1128/MMBR.65.1.1-43.2001
resistant to irreversible inactivation at high temperatures

Thermostable-protein review supports thermostable proteins as the mechanism enabling thermophile optima.

Temperature-optimum-high thermophile context

DOI-backed nonmechanistic graph connecting thermophile thermostability, genome thermostability, heat-shock protein-quality control, membrane-lipid remodeling, and amino-acid composition branches to the above-40-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.

Edge evidence

hot environment selects for thermophile protein thermostability METPO:2007401
Hot environments select for thermophile thermostable machinery.
- DOI:10.1016/s0300-9629(97)00003-0 adapted to environments of high temperature Supports hot environments as the context for thermophile optima.
thermophile protein thermostability confers temperature optimum high METPO:2007700
Thermophile thermostability yields a >40 °C optimum.
- DOI:10.1128/MMBR.65.1.1-43.2001 resistant to irreversible inactivation at high temperatures Supports thermostability as the mechanism producing thermophile optima.
temperature optimum high is a temperature optimum rdfs:subClassOf
Temperature optimum high is a quantitative bin of the temperature-optimum phenotype.
- DOI:10.1016/s0300-9629(97)00003-0 adapted to environments of high temperature Supports the >40 °C optimum as a value within the temperature-optimum distribution.
reverse gyrase positively regulates DNA positive supercoiling RO:0002213
Reverse gyrase introduces positive supercoils into DNA, a thermophile hallmark.
- DOI:10.1264/jsme2.me23087 introduces positive supercoils into DNA Verified against the open Takemata minireview; reverse gyrase is described as the characteristic thermophile topoisomerase that introduces positive supercoils into DNA.
DNA positive supercoiling decreases DNA melting at high temperature RO:0002212
Positive supercoiling limits DNA melting and prevents thermal denaturation.
- DOI:10.1264/jsme2.me23087 prevents the thermal denaturation of DNA Verified against the open Takemata minireview; the review presents reverse-gyrase-dependent positive supercoiling as the accepted route limiting DNA thermal denaturation.
nucleoid-associated proteins increases genome thermostability RO:0002213
Nucleoid-associated proteins enhance DNA/genome thermostability.
- DOI:10.1264/jsme2.me23087 increase the melting temperature of DNA Verified against the open Takemata minireview; in vitro studies of NAPs from prokaryotes show increased DNA melting temperature, and archaeal NAP abundance is correlated with growth temperature.
small heat shock proteins prevents heat-induced protein aggregation RO:0002212
Small heat shock proteins bind denaturing proteins to prevent heat-induced aggregation.
- DOI:10.1128/mbio.03593-22 protecting them from aggregation Verified against the open Baes et al. introduction; small archaeal heat-shock proteins are described as binding denaturing proteins to protect them from aggregation.
thermosome (group II chaperonin) enables refolding of denatured proteins RO:0002327
The thermosome enables ATP-dependent refolding of denatured proteins.
- DOI:10.1128/mbio.03593-22 refolds denatured proteins in an ATP-dependent manner Verified against the open Baes et al. introduction; the archaeal thermosome is described as the group-II chaperonin complex that performs ATP-dependent refolding of denatured proteins.
altered membrane lipid composition contributes to cytoplasmic membrane thermostability RO:0002326
Altered membrane lipid composition contributes to cytoplasmic membrane thermostability at high temperature.
- DOI:10.1128/mbio.03593-22 altered lipid composition of the cytoplasmic membrane Verified against the open Baes et al. introduction; Sulfolobales heat shock is described as altering cytoplasmic-membrane lipid composition, matching this as a membrane-stabilization response branch rather than a single determinant of thermophily.
hydrophobic and charged amino acid enrichment increases thermophile protein thermostability RO:0002213
Enrichment in hydrophobic and charged amino acids increases protein thermostability.
- DOI:10.1128/mbio.02174-23 enrichment in hydrophobic and charged amino acids Verified against the open Grünberger et al. introduction; the review context lists hydrophobic and charged amino-acid enrichment among molecular mechanisms used by hyperthermophilic archaea.
DNA positive supercoiling associated with genome thermostability biolink:associated_with
Reverse-gyrase-linked positive DNA supercoiling is associated with thermophile genome-thermostability context.
- DOI:10.1264/jsme2.me23087 protect genomes at high temperatures Verified against the open Takemata minireview; this connector keeps positive DNA supercoiling as one genome thermostability branch.
genome thermostability associated with thermophile protein thermostability biolink:associated_with
DNA and genome thermostability are associated with the broad thermophile-thermostability context.
- DOI:10.1264/jsme2.me23087 enhancing the thermostability of DNA in thermophiles Verified against the open Takemata minireview; this connector keeps nucleoid-associated proteins as DNA thermostability context.
heat-induced protein aggregation associated with refolding of denatured proteins biolink:associated_with
Heat-induced protein-aggregation prevention and denatured-protein refolding are associated heat-shock protein-quality-control branches.
- DOI:10.1128/mbio.03593-22 Small HSPs (sHSPs) and prefoldin bind to denaturing proteins Verified against the open Baes et al. introduction; this connector joins complementary small-HSP protection and thermosome refolding context for heat-damaged proteins.
refolding of denatured proteins associated with thermophile protein thermostability biolink:associated_with
Thermosome-linked refolding of denatured proteins is associated with the broad thermophile-thermostability context.
- DOI:10.1128/mbio.03593-22 thermosome complexes with different subunit compositions and substrate specificities Verified against the open Baes et al. introduction; this connector keeps thermosome refolding as protein-quality context.

Provenance

Identifier source: METPO (2026-06-12)
Definition source: DOI:10.1016/s0300-9629(97)00003-0

Parent traits (1)

temperature optimum METPO:1000304

Synonyms (2)

Thermophile EXACT_SYNONYM · metpo.owl
TO_>40 RELATED_SYNONYM · metpo.owl

kg-microbe context

Matched 1 kg-microbe node via direct_metpo.

METPO:1000447 [+1.114, +1.991, -0.944, +1.377, …]

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).

environment temperature range high 0.561
environment thermophilic 0.477
environment pH range mid1 0.447
environment pH range mid2 0.446
environment pH range low 0.444
environment temperature delta mid2 0.434
environment temperature delta high 0.429
environment temperature optimum 0.428

Deep research

Generated by just research-trait; source: research/traits/environment/temperature_optimum_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 **temperature optimum high**

**Trait:** “temperature optimum high”
**Identifier:** **METPO:1000447**
**Category / kind / status:** ENVIRONMENT / CLASS / REVIEWED
**Parent:** METPO:1000304
**Operational definition:** best-growth ambient temperature above approximately 40 °C, characteristic of thermophilic physiology.

## 1. Scope and boundaries

This trait should represent an **organism-level growth optimum**, determined from a growth-rate or biomass-yield curve across temperatures. It is not equivalent to: (i) survival after acute heat shock, (ii) maximum permissive growth temperature, (iii) heat resistance of spores or resting cells, or (iv) thermostability of an isolated protein. Those properties can be mechanistic contributors or associated phenotypes, but do not establish **METPO:1000447** by themselves.

The approximately 40 °C threshold includes moderately thermophilic organisms and creates boundary cases near 40–45 °C. Classification schemes vary: one recent synthesis subdivides thermophiles into moderate thermophiles at roughly 50–60 °C, extreme thermophiles at 60–80 °C, and hyperthermophiles at 80–110 °C. These narrower labels should not replace the supplied METPO cutoff (pandey2026extremethermalenvironments pages 5-6).

A robust annotation should therefore record: medium composition, pH, oxygen/electron donor and acceptor, pressure, salinity, temperature spacing, growth metric, replicate number, and fitted optimum. This matters because temperature optimum is conditional: changing salinity, pressure, pH, or substrate can shift apparent growth performance.

### Closely related but distinct traits

- **Thermotolerance/heat resistance:** survival or retained growth after supra-optimal heat exposure. For example, an *E. coli* screen at 47 °C identified high-temperature survival genes, but *E. coli* remains mesophilic; those results support generic heat-damage mechanisms, not a thermophilic optimum (murata2011molecularstrategyfor pages 1-2).
- **Protein thermostability:** resistance of a protein to irreversible inactivation. It is a molecular property and plausible enabling mechanism, not an organismal optimum.
- **Hyperthermophily:** a narrower high-temperature class, commonly associated with optima ≥80 °C. Reverse gyrase evidence below is strongest in this range and should not be generalized automatically to organisms with optima of 41–60 °C.
- **High maximum growth temperature:** an organism may grow weakly at a high temperature while having a lower optimum.
- **Acclimation:** reversible lipid, solute, or expression changes after a temperature shift; distinct from the evolved trait setpoint.

## 2. Mechanistic model and candidate nodes

The current understanding is **multifactorial**. High-temperature growth requires maintenance of macromolecular structure, DNA topology and repair, membrane permeability, translation/protein quality control, and energy balance. No single mechanism is universal across Bacteria and Archaea.

### Environmental and assay nodes

- high ambient temperature / cultivation temperature
- temperature gradient assay
- optimal growth temperature
- supra-optimal heat stress
- pH, salinity, hydrostatic pressure, oxygen concentration
- electron-donor and electron-acceptor availability
- specific growth rate and maximum cell density
- target trait: **METPO:1000447**

### Organisms and taxonomic contexts

- *Pyrococcus furiosus* — hyperthermophilic archaeon; direct reverse-gyrase and compatible-solute experiments
- *Thermococcus kodakarensis* — hyperthermophilic archaeal genetic model
- *Saccharolobus islandicus* and *Sulfolobus acidocaldarius* — thermoacidophilic archaeal membrane models
- *Thermus thermophilus* — extreme-thermophile bacterial model
- *Escherichia coli* — mesophilic heat-stress comparator, **not** direct evidence for thermophile optimum
- *Kluyveromyces marxianus* — thermotolerant yeast engineering context

Use NCBITaxon identifiers only after strain/species verification in the source. A broad node such as **NCBITaxon:2157** (Archaea) is safe but less informative than source-specific organism nodes.

### Genes, proteins, and complexes

- **reverse gyrase / rgy** — ATP-dependent topoisomerase and DNA-binding heat-protective factor; exact UniProt accession is strain-specific
- **GrsA and GrsB** — radical-SAM GDGT ring synthases; label-only until organism-specific protein accessions are verified
- **DnaK/DnaJ/GrpE**, **GroEL/GroES**, archaeal thermosome/chaperonin
- **ClpB/ClpG**, Lon, HslUV, FtsH, DegP — disaggregation/proteolysis modules
- **Phr** — archaeal heat-response transcriptional regulator implicated in DIP-pathway regulation
- **MPGS** — mannosyl-3-phosphoglycerate synthase
- **IPCT/DIPPS** — enzymes used in di-myo-inositol-phosphate biosynthesis
- DNA repair, tRNA modification, translation-control, and cell-division systems identified in high-temperature screens

Showing the first 60 of 248 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.

Saccharolobus islandicus NCBITaxon:43080 DOI:10.3389/fmicb.2023.1219779 Thermoacidophilic archaeon whose optimal growth temperature is reported as 76 degrees C, the one explicitly stated optimum in this trait's research artifact; the multi-omics study contrasts that optimum against 66 degrees C cold stress.

Curation history

2026-05-05T01:35:46.822120+00:00 · SEEDED_FROM_METPO · seed_from_metpo
imported from data/raw/metpo.owl (CLASS)
2026-05-13T11:00:00-07:00 · CURATED_CAUSAL_GRAPH · claude
Added DOI-backed definition and causal graph linking thermophile thermostability to the temperature-optimum-high bin.
2026-05-20T03:35:30Z · GROUND_CAUSAL_PREDICATES · claude
Grounded 2 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (METPO:2000202×1, rdfs:subClassOf×1).
2026-05-23T21:30:06Z · GROUND_CAUSAL_PREDICATES · claude
Grounded 1 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (METPO:2007401×1).
2026-06-23T00:00:00Z · ENRICH_CAUSAL_GRAPH · claude
Added 7 evidence-backed generic edges (12 new nodes) from the deep-research report.
2026-06-24T17:21:11Z · GROUND_CAUSAL_PREDICATES · claude
Grounded 4 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (RO:0002213×2, METPO:2000017×1, RO:0002212×1).
2026-06-24T17:21:17Z · GROUND_CAUSAL_NODES · claude
Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv (UniProtKB:A0A088E825×1).
2026-07-20T04:21:11Z · RETRACT_DEAD_UNIPROT_GROUNDINGS · claude
Retracted 1 UniProtKB grounding(s) whose accessions are deleted from UniProt; nodes demoted to label-only pending re-grounding (docs/GROUNDING_POLICY.md)
2026-07-20T04:23:53Z · GROUND_CAUSAL_NODES · claude
Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv (GO:0160097×1).
2026-08-04T03:08:13Z · GROUND_CAUSAL_PREDICATES · claude
Grounded 1 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (RO:0002213×1).
2026-08-06T01:00:00Z · 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.
2026-08-06T02:00:00Z · 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.
2026-08-06T06:00:00Z · 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.
2026-08-20T08:00:00Z · BACKFILL_CANONICAL_EXAMPLES · claude
Added one exemplar taxon, Saccharolobus islandicus, whose 76 C optimal growth temperature is the one optimum this trait's own deep-research artifact explicitly states, inside the >40 C bin. Taxon id resolved and label-checked against the local NCBITaxon build. Deliberately excluded - Pyrococcus furiosus (its 90 C cultivation is the study's control condition against 98 C 'supra-optimal' heat stress; the artifact never states its optimum) and Thermococcus kodakarensis (one wild-type growth-rate measurement at 85 C; the 75 and 93 C series endpoints are delta-rgy mutant data, so no optimum is established) -- both were in the first draft of this backfill and removed on review; Escherichia coli and Kluyveromyces marxianus, which the artifact names only as heat-stress/thermotolerance comparators and explicitly disqualifies (E. coli "remains mesophilic"; the CYR1 work concerns "an engineered thermotolerance phenotype rather than proof that CYR1 establishes a natural >40 C optimum"); and Thermococcus barophilus, Thermus thermophilus and Sulfolobus acidocaldarius, which appear in the artifact with no cited optimum-temperature measurement.
2026-08-21T08:00:00Z · NORMALISE_NODE_TYPE · codex
Tranche 5 of issue 356 settles the process/quality families and merges ids that meant the same sense: dna_positive_supercoiling is BIOLOGICAL_PROCESS. GO:0160097 denotes the process of introducing positive supercoils into DNA. The general DNA-topology state remains separately modelled as dna_supercoiling.
2026-08-26T03:23:00Z · 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_high_thermophile_setpoint=NONMECHANISTIC with scope_notes; marked 3 GENE_OR_PROTEIN node(s) REVIEWED_LABEL_ONLY with grounding_notes (nucleoid_associated_proteins, small_heat_shock_proteins, thermosome).
2026-09-04T03:20:00Z · REVIEW_CAUSAL_EVIDENCE · codex
Reviewed the temperature_optimum_high_thermophile_setpoint graph for issue #183: added snippets to 7 edge-level evidence items and grounded the thermosome and membrane-lipid predicates to RO:0002327 or RO:0002326. No paid research service was called.
2026-09-04T20:00:00Z · 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 genome thermostability, small-HSP/thermosome protein quality control, and membrane-thermostability branches. No paid research service was called.
2026-09-06T17:10:00Z · ADVERSARIAL_REVIEW_REPAIR · codex
Addressed PR #664 adversarial review: replaced copied nonmechanistic bridge snippets with independent exact source snippets while preserving the existing connector edge scope.
2026-09-08T03:05:00Z · ADVERSARIAL_REVIEW_REPAIR · codex
Addressed PR #664 adversarial review issue #700: removed the membrane-thermostability to thermophile-thermostability connector whose Baes et al. quote only supported broad heat-damage context.
2026-09-08T03:30:00Z · ADVERSARIAL_REVIEW_REPAIR · codex
Addressed PR #664 adversarial review issue #702: appended corrective issue-183 provenance after evidence-weak connectors were pruned; this NONMECHANISTIC graph intentionally ships with 2 disconnected components until independent trait-specific connectors are curated.