The amoeba that refused to cook
Geothermal landscape in Lassen Volcanic National Park. This is not the discovery site (photo by Royce Fonseca on Unsplash)
At California’s Lassen Volcanic National Park, it is easy to find water that looks too hot to touch. Steam rises from geothermal pools, and the ground around them can be unstable. Biologists looking for heat-loving organisms came prepared with long sampling tools.
Their most surprising find came from a narrow tributary that looked rather ordinary. The space was awkward to reach, so the researchers used barbecue tongs to collect a sample. They took it back to Syracuse University, put it in an incubator and waited to see what might grow.
Among the organisms that appeared was an amoeba, a single cell that moves by pushing out parts of its flexible body. It grew at 57°C. The team raised the temperature. At 60°C, it kept growing. At 63°C, the amoeba was still dividing into new cells.
No other known eukaryote had been shown to reproduce at that temperature. Eukaryotes are organisms whose cells contain a nucleus and other internal compartments. Animals, plants and fungi belong to this vast group, as does the amoeba the researchers named Incendiamoeba cascadensis: roughly, “fire amoeba from the Cascades”. The findings appeared as a preprint in 2025 and were published in the journal Cell in September 2026.
How hot can a complex cell get?
Why is 63°C remarkable? After all, some microbes live in water that is far hotter.
The answer lies partly in how a eukaryotic cell is built. Its nucleus houses its DNA, while other membrane-bound compartments carry out specialised jobs. Proteins must fold into the right shapes to perform thousands of tasks, from processing nutrients to repairing damage.
Heat puts this organisation under strain. Proteins can lose the shapes that make them useful, and membranes can become unstable. A cell might survive a brief spell of heat yet be unable to perform the carefully coordinated work of making another cell.
Bacteria and archaea include extraordinary heat specialists. Eukaryotes seemed to face a lower limit: before this discovery, the highest known growth temperature was around 60°C, reached by a few fungi and red algae. The researchers have now moved that observed boundary by three degrees.
They did more than count cells accumulating in warm flasks. They tested growth across a range of temperatures and used microscopy to observe the amoeba dividing. That made 63°C a record for reproduction, rather than simply a temperature it could endure.
Then they pushed further. At 64°C, it could still move, although it was no longer reproducing. At 70°C, it survived a short exposure by forming a protective dormant cyst and resumed activity when conditions cooled. NASA reports recovery after five minutes at 70°C; an exposure to 80°C was too much for it.
Its limits therefore depend on what the cell is being asked to do. It can multiply at 63°C, remain mobile at 64°C and recover from a brief encounter with 70°C by shutting down. Calling it an organism that “lives at 70°C” would give quite the wrong picture of its ordinary day.
Dinner in a hot stream
The fire amoeba does more than withstand its surroundings. It hunts.
Researchers watched it feed on filament-shaped bacteria: long, threadlike cells that it envelops with a protrusion of its body. In a microscopic image published by Syracuse University, a bacterial filament bends as the amoeba draws it in. The predator has no jaws or claws. Its flexible cell does the work.
That helps bring its habitat to life. Bacteria grow in the heated water, and the amoeba eats them. Tolerating such temperatures might give it access to food with fewer competitors or predators around, though the study did not establish whether that is why this species evolved its heat tolerance.
Could the fire amoeba inspire heat-resistant technology?
The team has begun looking for an explanation inside the cell. They sequenced its genome and studied how gene activity changed at different temperatures. They found genes associated with protecting DNA, maintaining proteins and sensing the environment. Some genes involved in keeping proteins properly folded became more active in the heat. The researchers also identified properties of certain proteins that might help them remain stable. They have leads, but do not yet have a complete account of how the amoeba survives.
Those leads could eventually be useful outside biology. Industry employs enzymes (proteins that speed up chemical reactions) in processes where heat can damage ordinary versions. Discovering how this amoeba protects its cellular machinery might inspire heat-resistant enzymes or other resilient materials.
There may be more amoebae like it. When the team compared genetic data from other geothermal sites, they found signs of related organisms in places including Yellowstone National Park and New Zealand. Those clues do not establish that the relatives share its extraordinary temperature record, but they give researchers somewhere to look.
For scientists studying where life can exist, Incendiamoeba has replaced a presumed limit with a measured one. Temperature is only part of the story: this amoeba also needs suitable water chemistry, oxygen and food. It cannot thrive in a hot place merely because the thermometer reads 63°C.
Under the microscope, it wraps itself around a long bacterium and draws its meal inside. Its water is hot enough to scald us. Its intricate cell, somehow, is still working.
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