A newly described amoeba from a geothermal stream in California can reproduce at 63°C, setting a new documented heat record for eukaryotes, the group of organisms whose cells contain a nucleus. Researchers at Syracuse University reported the finding in the peer-reviewed journal Cell on September 22. The species, named Incendiamoeba cascadensis, raises the known upper temperature limit for growth of complex cells by three degrees.
Scientists had previously documented eukaryotic growth at temperatures up to about 60°C, while some bacteria and archaea tolerate far greater heat. That distinction matters because a nucleus and other internal cell structures must remain functional for a eukaryote to divide. The new result concerns one microscopic species; it does not mean animals or people can withstand comparable temperatures.
Led by doctoral researcher H. Beryl Rappaport and biologist Angela Oliverio, the team collected organisms from a tributary of Hot Springs Creek in Lassen Volcanic National Park between 2023 and 2025. They then cultured the amoeba at a range of controlled temperatures. Growth experiments and microscopy showed that its cells continued to divide at 63°C, rather than merely remaining alive in hot water.
The investigators also observed movement at 64°C. At 70°C, the amoeba formed a protective cyst and could recover after temperatures fell, according to the university and Cell Press. These are different thresholds: the study documents reproduction at 63°C, movement at 64°C and survival after exposure at 70°C. It does not show that the organism grows at 70°C.
Genome comparisons found an enrichment of genes linked to protein maintenance, DNA stability and sensing the environment. The researchers also identified protein features associated with heat stability in other microbes. Those findings offer possible explanations for its tolerance, but further experiments are needed to establish exactly how each adaptation works.
The result widens the range of environments in which scientists may look for eukaryotic life, including other geothermal sites. Syracuse University says the organism may also inform future work on heat-stable enzymes and materials, though no practical application has been demonstrated. Further research can examine other hot environments and the cellular mechanisms that keep this amoeba functioning.
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