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A heat-loving amoeba discovered in California’s Lassen Volcanic National Park has pushed the known thermal limits of complex life. Scientists say the single-celled organism can reproduce at temperatures higher than any previously observed eukaryote and survives short bursts of even hotter conditions.
Record temperatures for complex cells
Researchers identified the species, named Incendiamoeba cascadensis, living in a tributary of Hot Springs Creek. In laboratory observations the amoeba divided and grew at temperatures up to 145°F (63°C), a new high for cells with nuclei.
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Under brief exposure the cells formed protective shells and endured 158°F (70°C) for several minutes before recovering when temperatures were lowered to 140°F. They did not survive heating to 176°F (80°C).
Where the organism thrives
The team found the amoebas in geothermal waters inside the park. Unlike many organisms that prefer cooler conditions, these amoebas appeared to need heat: they stopped growing below about 108°F (42°C) and proliferated most actively between 131°F and 135°F (55–57°C).
How the discovery unfolded
Study first author Beryl Rappaport, a microbiologist at Syracuse University, said the results surprised the team. “I was very surprised,” she told Live Science. “We definitely had to go back and check to make sure that our incubators were calibrated correctly … It really was amazing.”
Molecular hints about heat resistance
Analyses of the amoeba’s biochemistry revealed that many of its proteins bear more positively charged amino acids on their surfaces. The researchers note this feature resembles adaptations seen in heat-tolerant prokaryotes and may help maintain protein stability at high temperatures.
How eukaryotes differ from prokaryotes
Although some bacteria and archaea can tolerate far hotter environments—prokaryotes have been recorded surviving temperatures near 250°F (122°C)—eukaryotic cells generally hit an upper bound much lower than that. Some desert fungi, for example, can endure temperatures up to about 140°F, but those tolerances still fall short of many prokaryotic extremes.
Rutgers evolutionary biologist Debashish Bhattacharya, who was not involved in the study, pointed to a key difference in adaptability between the two groups. “When you’re a bacterium … you can reshuffle your genome,” he told Live Science, noting prokaryotes can more readily acquire new genes. In contrast, he said, because eukaryotic DNA is sequestered inside a nucleus, “eukaryotes are not able to simply grab a bunch of genes and switch their lifestyle.”
Scientific and broader implications
The researchers published their results on Sept. 22 in the journal Cell. They say studying the amoeba and its close relatives could clarify why most eukaryotes fail to tolerate higher temperatures and help define the boundaries for complex life on Earth.
Understanding these adaptations also contributes to questions about where complex life might be possible elsewhere in the universe, the authors add, while offering fresh insight into the diversity of life in geothermal environments.
