For decades, biologists relied on a simple rule of thumb: above 60°C (140°F), complex cells can’t survive. A tiny amoeba collected from a volcanic stream in California has just proved that rule wrong. Named Incendiamoeba cascadensis, the “fire amoeba of the Cascades”, it keeps dividing at 63°C (145°F), a new record for eukaryotic life. The study was published in Cell.
A discovery found far from the famous hot pools
The research was led by biologists Angela Oliverio and Beryl Rappaport of Syracuse University, working with Gordon Wolfe (Chico State University) and Ken Stedman (Portland State University). The team sampled geothermal sites in Lassen Volcanic National Park, whose wide range of hot, chemically diverse springs makes it an ideal natural laboratory.
Yet the amoeba didn’t come from the park’s well-known acidic pools. It turned up in a small, unremarkable tributary. Fieldwork meant using extra-long tools to stay clear of boiling water and fragile ground, and in the stream’s tightest spots the researchers improvised with barbecue tongs.
How the amoeba handled rising heat
Back in the lab, the team gradually raised incubator temperatures. The results:
- between 57°C and 60°C, the amoebae kept growing;
- at 63°C, they were still dividing, a record for any eukaryote;
- at 64°C, they were still moving;
- at 70°C, they formed cysts, dormant structures that reactivate once temperatures drop.
Rappaport told Live Science the result was so unexpected that the team double-checked their incubator calibration before trusting it.
The genes behind the heat tolerance
The researchers sequenced the organism’s full genome and tracked which genes switched on at different temperatures. They found genes that protect and stabilise DNA, others involved in sensing the environment, and more that help proteins keep their shape under heat stress. Comparing its genetic code with DNA from other geothermal waters suggests relatives may live in New Zealand and Yellowstone.
Why it matters: from astrobiology to biotech
According to Oliverio, the finding shows that long-held assumptions were wrong and that many more heat-tolerant eukaryotes may still be undiscovered. Expanding the known thermal range of complex life also widens the places worth searching for it, on Earth and on other planets.
There could be practical payoffs too: the membrane and protein adaptations of I. cascadensis might inspire heat-stable enzymes, tougher biomaterials and high-temperature bioprocesses.
Extreme microbes in unexpected places
Oliverio’s lab is already using the same culturing methods closer to home. Students are studying a steam pipe on the SUNY College of Environmental Science and Forestry campus and finding that heat-loving microbes aren’t limited to hot springs and deep-sea vents: they can also colonise human-made environments.
The researchers’ takeaway is simple: the boundaries of life aren’t always where scientists expect them, and the search should go further.