New 'Fire Amoeba' Sets Heat Record for Complex Life — Survives and Reproduces Above 63 °C

Summary: Scientists have discovered a previously unknown single-celled eukaryote that reproduces at temperatures higher than any other complex organism known to date. Described in a preprint on bioRxiv and not yet peer-reviewed, the organism challenges long-held limits on how much heat eukaryotic life can tolerate.

Discovery In A Hot Stream

Syracuse University microbiologist Angela Oliverio and graduate student Beryl Rappaport collected water and sediment from a hot stream in Lassen Volcanic National Park in northern California. Back in the lab, after incubating samples at stream-like temperatures, the team isolated an amoeba unlike any they had seen and identified it as a new species: Incendiamoeba cascadensis (literally, “fire amoeba from the Cascades”).

Heat Tolerance That Redraws Boundaries

The organism can replicate at up to 63 °C (145 °F), remains metabolically active at 64 °C (147 °F), and can form a protective encysted state that survives brief exposure to 70 °C (158 °F), reactivating when temperatures fall. Until now, eukaryotes were thought to struggle above ~62 °C; previously documented eukaryote tolerance topped out near 60 °C.

Molecular Clues

The researchers sequenced the amoeba’s genome and analyzed its predicted proteome. Their data indicate that the proteins this amoeba produces have a higher average melting temperature than those of its closest amoebal relatives — a plausible molecular basis for its unusual thermotolerance.

Context: How Hot Can Life Get?

Most extremophile research has focused on bacteria and archaea, simpler cells that lack a nucleus. The highest-temperature record for any organism is held by the archaeon Methanopyrus kandleri, which grows near 122 °C (≈252 °F). Heat-tolerant bacteria such as Geothermobacterium ferrireducens can grow up to about 100 °C (212 °F). The new finding narrows the gap in our understanding of eukaryotic versus prokaryotic thermal limits.

Implications

Beyond revising eukaryotic thermal limits, the discovery has practical and scientific implications. Heat-stable eukaryotic proteins could be valuable for industrial enzymes and biotechnology applications (for example, more effective detergents or robust biocatalysts). The result also matters for astrobiology: it expands the kinds of environments where complex life might conceivably exist.

“The difference between 60 °C and 63 °C may sound small but represents a relatively large shift in our current understanding of eukaryotic limits,” said microbial ecologist and astrobiologist Luke McKay (not involved in the study).

Caveat: The findings are reported in a preprint on bioRxiv and have not yet undergone peer review. Further study will confirm the limits, ecological role, and biochemical mechanisms behind Incendiamoeba cascadensis’s heat tolerance.