Scientists Discover 'Fire Amoeba' That Divides at a Record 145.4°F

Scientists Discover Heat-Tolerant "Fire Amoeba" at Lassen

Parts of Lassen Volcanic National Park in California’s Cascade Range host steaming pools and bubbling mud where temperatures can reach extremes — some geothermal features approach 464°F — conditions lethal to humans and most life. Yet an international team of researchers has identified a tiny single-celled eukaryote that not only survives in hot spring water but actively divides at unusually high temperatures. The organism has been named Incendiamoeba cascadensis (the “fire amoeba from the Cascades”).

New Record for Complex Life

The study, published last week but not yet peer-reviewed, reports that Incendiamoeba cascadensis remains motile and divides at 145.4°F, setting a new upper temperature record for eukaryotic (complex) life. The amoeba was active at the stream’s normal temperature (~134.6°F) and continued to function as the researchers gradually increased the temperature. At roughly 158°F, the organism entered dormancy by encysting — forming a protective, hard-shelled cyst that allows it to survive harsher conditions and later resume activity when temperatures fall.

How It Survives

Genomic sequencing of the organism revealed an enrichment of genes associated with proteostasis (protein maintenance), genome stability, and environmental sensing. These features likely help preserve cellular integrity and function at temperatures that would denature proteins and damage most eukaryotic cells.

“We need to rethink what’s possible for a eukaryotic cell in a significant way,” said Angela Oliverio, a study co-author and microbiologist at Syracuse University, in comments to Nature.

Context and Implications

Until now, the most heat-tolerant organisms were primarily prokaryotes (bacteria and archaeans). Prokaryotes remain capable of surviving at substantially higher temperatures — observed persistence ranges of roughly 149–221°F, with the archaeon Methanopyrus kandleri recorded at 251.6°F — and some theoretical chemistry-based limits extend even higher. Still, the discovery of a eukaryote able to divide at 145.4°F expands our understanding of thermal limits for cellular complexity.

The findings have practical and scientific implications: the amoeba’s thermostable proteins may be valuable for biotechnology, and the discovery broadens the range of conditions considered possible for complex life — a point of interest for astrobiology and the search for life in extreme environments on other worlds.

Where It Was Found

Researchers found the amoeba in a relatively ordinary, pH-neutral hot spring stream at Lassen rather than in the park’s acidic pools. Microscopic inspection of untreated stream water initially showed no obvious life, but when scientists added nutrients and warmed samples to the stream’s temperature range, the previously unseen amoeba became active.

The team cautions that the study is preliminary and not yet peer-reviewed, but they suggest that similar high-temperature eukaryotes could exist in other geothermal habitats and deserve closer attention.