New 'Fire Amoeba' Species Sets Temperature Record for Complex Life

Researchers at Syracuse University have described a previously unknown amoeba species — Incendiamoeba cascadensis, or "fire amoeba from the Cascades" — capable of growing and dividing at 63°C (145°F), exceeding the established upper temperature limit for all known eukaryotic organisms. The findings appear in a preprint on bioRxiv and were independently covered in Nature; the study is currently awaiting formal peer review.

Key developments

• Discovery and collection: Microbiologists Angela Oliverio and Beryl Rappaport of Syracuse University collected samples from geothermal streams at Lassen Volcanic National Park in northern California's Cascade mountain range. Within weeks of laboratory cultivation, the team observed a never-before-seen amoeba species growing in flasks maintained at temperatures matching the stream environment.

• Records surpassed: Eukaryotes — organisms whose cells contain a nucleus, encompassing animals, plants, fungi, and protists — had not previously been confirmed to replicate above approximately 60–62°C. I. cascadensis divides at 63°C, remains active at 64°C, and at temperatures up to 70°C forms dormant protective cysts that revive once the environment cools. A prevailing assumption dating to the early 1970s held that the greater cellular complexity of eukaryotes imposed a stricter thermal ceiling compared with bacteria or archaea.

• Molecular adaptations: Genome and proteome analysis revealed that the amoeba's core proteins carry a higher average melting temperature than those of its nearest known relatives, suggesting specific molecular adaptations — rather than a general tolerance — underpin its heat resistance.

• Astrobiology context: Microbial ecologist and astrobiologist Luke McKay, commenting on the study for Scientific American, said the discovery pushes "the boundaries of our understanding of life's limits on Earth and the implications for life beyond Earth — where else and how else life might be able to take hold and thrive." Researcher Oliverio noted that environmental DNA matching the find has been detected at other geothermal sites, including Yellowstone.

What to watch

The bioRxiv preprint describing I. cascadensis has not yet completed formal peer review, meaning the species description, temperature record, and genomic conclusions remain provisional. Independent replication and full peer-reviewed publication are the primary milestones needed to confirm these results.

Because sampling was limited to a single geothermal stream at Lassen, follow-up surveys at Yellowstone and geothermal areas in New Zealand and elsewhere may determine how widespread I. cascadensis or similarly heat-adapted eukaryotes actually are, and whether even higher thermal limits exist.

Sources

• A geothermal amoeba sets a new upper temperature limit for eukaryotes — bioRxiv preprint (Oliverio et al., 2025)
• Nature News: A tiny amoeba has broken a pretty big record (doi:10.1038/d41586-025-03933-5)
• ScienceAlert: Extreme 'Fire Amoeba' Smashes Record For Heat Tolerance
• CDC: Naegleria fowleri and free-living ameba background