Researchers have identified a new record-holder for heat tolerance among complex organisms: an amoeba species capable of surviving and reproducing at temperatures exceeding 145 degrees Fahrenheit (63 degrees Celsius). This organism, named Incendiamoeba cascadensis and nicknamed the fire amoeba, was discovered in the hot, algae-covered streams of Lassen Volcanic National Park in California. The findings were published last week in the journal Cell.
The fire amoeba demonstrates mobility at temperatures as high as 147 degrees Fahrenheit (64 degrees Celsius), surpassing the previous heat tolerance threshold for eukaryotes—organisms with cells containing nuclei and membrane-bound organelles. Prior to this discovery, the highest known temperature tolerance for complex life was approximately 140 degrees Fahrenheit, based on studies of fungi.
A team led by microbiologist Angela Oliverio of Syracuse University collected water and sediment samples from geothermal streams in Lassen Volcanic National Park between 2023 and 2025. They cultivated the microorganisms in laboratory incubators to determine the temperatures at which the fire amoeba remains active and capable of reproduction. While some simpler organisms, such as bacteria and archaea, can tolerate even higher temperatures, their cellular simplicity distinguishes them from eukaryotes like the fire amoeba.
The researchers conducted genomic sequencing of Incendiamoeba cascadensis to understand the mechanisms enabling its exceptional heat resilience. Their analysis suggests that the amoeba’s outer membrane may contain specialized proteins that form a highly protective layer, shielding it from the extreme temperature conditions present in its volcanic habitat.
Adrienne Kish, a microbiologist at the National Museum of Natural History in Paris who was not involved in the study, highlighted the significance of these findings. She emphasized the importance of exploring extreme environments on Earth, noting that unusual organisms such as the fire amoeba provide insight into biological adaptations and the potential existence of other undiscovered extremophiles.
The study authors anticipate that further investigation of Lassen Volcanic National Park’s geothermal streams could reveal additional heat-tolerant species, expanding understanding of life’s boundaries in extreme conditions.