Scientists Discover a 'Fire Amoeba' in Lassen That Reproduces at 145°F

New Heat‑Tolerant Eukaryote Found in Lassen Volcanic National Park

Hot water shapes much of the terrain at Lassen Volcanic National Park, where hydrothermal zones produce steam, volcanic gas vents, mud pots and boiling pools. In waters once thought too hot for complex single‑celled life, researchers have identified a new eukaryotic amoeba that can survive — and reproduce — at temperatures higher than previously believed possible.

Beryl Rappaport, a microbiologist completing her Ph.D. at Syracuse University, led the team that discovered the organism. They named it Incendiamoeba cascadensis — literally the “fire amoeba of the Cascade Range” — in reference both to its heat preference and its discovery site in the Cascades.

Record‑breaking Heat Tolerance. The team reports that the amoeba can reproduce at roughly 145°F (≈62.8°C), exceeding the prior upper limit of about 140°F (≈60°C) recorded for similar eukaryotes such as certain red algae and fungi. The finding is described in a preprint that has not yet undergone peer review.

How It Was Found. Researchers collected water samples from a small, steaming tributary of Hot Springs Creek, near a hiking trail. In the lab they used culturing methods to activate and grow the amoebas, placing cultures into incubators set at progressively higher temperatures. The incubator’s previous maximum, about 135°F (≈57.2°C), was surpassed as cultures continued to thrive and the team raised temperatures repeatedly to confirm sustained growth.

“Eukaryotes can grow at higher temperatures than we thought was possible for them,” Rappaport said.

Why It Matters. Discoveries that push known thermal limits help scientists refine models of life’s boundaries on Earth and guide the search for life beyond our planet. The team plans to sequence the amoeba’s genome to identify genetic adaptations or molecular mechanisms that enable heat tolerance. Because proteins typically denature at high temperatures, researchers suspect this organism may possess unique structural features or stress‑response systems that protect cellular machinery in extreme heat.

Other microbes — especially many bacteria and archaea — are known to survive at even higher temperatures, and some reports cite multicellular organisms such as tardigrades in extremely hot environments (for example, conditions cited above ~235°F / ~112.8°C under special circumstances). Similar heat‑loving microbes have been found in hot springs worldwide, including New Zealand.

Rappaport said she hopes to expand sampling to hot springs globally to learn whether related species exist at even higher temperatures. “There’s no reason we couldn’t find something else growing at an even higher temperature somewhere else,” she said.

Note on Status. The results appear in a preprint and have not yet been peer‑reviewed; further study and independent replication will help confirm and contextualize the findings.