A tiny, single-celled organism can thrive at temperatures that would kill all other known complex life. In a study publishing September 22 in the Cell Press journal Cell , scientists describe a new species of amoeba that can eat and reproduce in hot spring water as warm as 63°C (145°F) in California’s Lassen Volcanic National Park. The amoeba can protect itself at temperatures up to 70°C (158°F) by changing shape and forming a protective outer layer.
“This finding pushes the bounds of what we thought was possible, which is incredibly exciting,” says corresponding author Angela Oliverio of Syracuse University. “There could be more eukaryotes that can survive at even higher temperatures than we know of.”
The record for the hottest-growing organism belongs to Methanopyrus kandleri , an archaeon and relatively simple microorganism that lives at 122°C (252°F) around hydrothermal vents in the deep ocean. For decades, researchers have considered 60°C (140°F) to be the upper limit for eukaryotes, which are organisms with complex cells, such as animals, plants, fungi, and some microbes. Only a handful of eukaryotes can grow at temperatures approaching that limit.
Previous studies have found traces of amoebae—single-celled microorganisms that can change shape—near geothermal springs, where the water temperatures can exceed 140°F. But scientists had not thoroughly studied these species to verify that they could cope with extreme heat. So, Oliverio and her team set out to do just that.
Between 2023 and 2025, the researchers collected organisms from geothermal streams in the Lassen Volcanic National Park in California’s Cascade Range, where water temperatures at the sampling sites ranged from about 47°C to 64°C (117°F to 147°F).
Among all the samples collected, one previously unknown amoeba stood out. The organism grew robustly at 57°C (135°F) in the lab, the highest temperature previously known for amoeba growth. So, the team kept raising the temperature. At 63°C (145°F), they saw the amoeba undergoing mitosis, a process by which eukaryotic cells divide. This confirmed that it could not only survive but also thrive at temperatures beyond the previously recognized limit for eukaryotes.
The researchers named the new species Incendiamoeba cascadensis , roughly translating to “fire amoeba from the Cascades.” They found that the fire amoeba can protect itself by changing shape and forming a protective outer layer when temperatures rise beyond 63°C (145°F). When the amoebae were exposed to 70°C (158°F), they were able to recover after returning to cooler temperatures.
By sequencing the amoeba’s genome, the researchers found that it has extra genes associated with protein maintenance and DNA repair that could help the organism cope with extreme heat compared with other amoebae that live in more mild environments.
The team also found that the fire amoeba’s proteins have more positively charged amino acids on their surfaces, a feature also seen in some of the most heat-tolerant bacteria and archaea, a type of single-celled microbe. These molecules may help keep proteins stable and prevent them from unfolding or clumping together under extreme heat.
“Even though these organisms are so different, there’s convergence in how protein properties are selected for stability under high temperatures,” says first author H. Beryl Rappaport, a doctoral student at Syracuse University.
Despite the fire amoeba breaking the previous record for eukaryotes by only a few degrees, Oliverio says the finding could inspire future research to test organisms’ environmental tolerance without preconceived limits.
“Every time we set a new world record in sports, it’s amazing and celebrated, even if it’s by milliseconds,” Oliverio says. “We should do the same for amoebae. These very small changes expand our understanding of what we think is possible.”
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This work was supported by the National Science Foundation, the National Aeronautics and Space Administration, The American Philosophical Society, the National Institutes of Health, the Howard Hughes Medical Institute, the Water and Life Interface Institute, the Alfred P. Sloan Foundation, Syracuse University, the European Commission, the European Molecular Biology Laboratory, the Swiss National Science Foundation, the Gordon and Betty Moore Foundation, and the Department of Energy.
Cell , Rappaport et al., “A geothermal amoeba sets a new upper temperature limit for eukaryotes” https://www.cell.com/cell/fulltext/S0092-8674(26)01016-0
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A geothermal amoeba sets a new upper temperature limit for eukaryotes
22-Sep-2026