A eukaryotic organism named Incendiamoeba cascadensis has shattered the known temperature limit for complex life, thriving at 63°C (145°F) and surviving brief exposure to 70°C (158°F), according to a study published in Cell in September 2026. The discovery, made in California’s Lassen Volcanic National Park, challenges assumptions about cellular stability and expands possibilities for astrobiology.
The organism, informally called the “fire amoeba,” was identified by Syracuse University researchers Angela Oliverio and Beryl Rappaport during fieldwork between 2023 and 2025. Samples collected from geothermal streams revealed an amoeba capable of active growth and reproduction at 63°C, six degrees higher than the previously accepted eukaryotic limit of 60°C. At 70°C, the amoeba formed a protective cyst, a dormant state from which it later recovered, though it could not sustain active growth at that temperature.
A Breakthrough in Thermal Biology
The study, led by Syracuse University, used gene-expression analysis and protein-stability data to uncover how I. cascadensis defies expectations. Comparing cellular activity at 48°C and 61°C, researchers observed increased expression of pathways linked to DNA repair and cellular integrity as temperatures rose. The amoeba’s proteins exhibited mechanisms similar to those found in heat-tolerant bacteria, suggesting convergent evolution in response to extreme environments.
In part, studies on eukaryotes may have been limited because of assumptions about membrane stability,
said Rappaport, the study’s lead author. “We are hoping that the discovery of I. cascadensis encourages others to keep searching for high temperature eukaryotes.” The findings, published in Cell, highlight the need to reevaluate how complex cells adapt to thermal extremes.
Implications for Astrobiology and Biotechnology
The discovery carries significant implications for astrobiology.
Extremophiles like I. cascadensis also offer insights into biotechnology.
Challenging the Eukaryotic Heat Threshold
Previously, eukaryotes were thought incapable of growing above 60°C due to the fragility of their membrane-bound organelles. I. cascadensis disproves this by maintaining cellular function at 63°C. At 64°C, it remained active, moving to seek food, but at 70°C, it entered a dormant cyst state. This distinction is critical: the record specifically applies to active growth, not temporary heat endurance.
The study underscores the value of underexplored ecosystems in expanding scientific understanding.
As scientists continue to probe life’s boundaries, I. cascadensis stands as a testament to nature’s resilience.