Researchers discovered a record-shattering microscopic amoeba in a California geothermal park that actively replicates at 145 degrees Fahrenheit, pushing the absolute temperature limits of complex life and outperforming previous benchmarks for cells equipped with a nucleus.
Deep inside the steaming geothermal pockets of Lassen Volcanic National Park, scientists have found an extremophile that rewrites the known thermal boundaries for eukaryotic organisms. Discovered along a tributary of Hot Springs Creek, the single-celled organism has been named Incendiamoeba cascadensis — the fire amoeba from the Cascades. While simple single-celled life like bacteria and Archaea regularly thrive in scalding environments well past the boiling point of water, complex cells with a membrane-bound nucleus have historically struggled once temperatures climbed past 140 degrees Fahrenheit.
That barrier has now moved.
Hot Springs Sampling in Lassen Volcanic National Park
Finding the record-breaking organism required fieldwork in one of the country’s less-traveled federal reserves. She says that there is a very deep curiosity and desire to understand life at its limits and at its most extreme, as well as where that boundary is and what our constraints truly are.
Beryl Rappaport, a PhD student and microbiologist in Oliverio’s lab, collected the crucial water samples from a small waterway channel. Rappaport and her colleagues reported their findings on Tuesday, Sept. 22, in the journal Cell, detailing how they dipped sample vials into the hot water using extra-long barbecue tongs to avoid the scalding runoff. According to Le Figaro, the work was funded in part by NASA.
Microscopic Movement and Cellular Limits
Back in the laboratory, Rappaport examined the collected water under a heated microscope designed to keep the samples toasty. When she sped up the recorded microscope footage, she spotted tendrils of cellular fluid pulling the organism forward.
That’s definitely an amoeba. That’s characteristic amoeba movement.
Beryl Rappaport, PhD student at Syracuse University
Under lab observation, the amoeba actively multiplied at 63 degrees Celsius (145 Fahrenheit) and continued moving and feeding slightly past that threshold at 64 degrees Celsius, as noted by Le Figaro. When researchers ratcheted the environment up to 158 degrees Fahrenheit (70 Celsius), the organisms went dormant by building protective shells around themselves. If kept at that extreme level for no more than five minutes before being cooled back down to 140 Fahrenheit, the cells managed to recover, though they perished completely when exposed to 176 Fahrenheit (80 Celsius).
Why Complex Heat Tolerance Remains Rare
The discovery highlights a fundamental evolutionary divide between prokaryotic and eukaryotic life. While bacteria can quickly swap genetic material with neighbors to rapidly adapt to harsh environments, eukaryotes keep their DNA sealed inside a nucleus, making swift lifestyle changes far more difficult. When analyzing the genomic makeup of Incendiamoeba cascadensis, the team discovered that its proteins feature positively charged amino acids on their surface, a stabilizing adaptation shared with heat-loving prokaryotes.
Purificación López-García, directrice de recherches au CNRS rattachée au laboratoire Écologie, société et évolution de l’université Paris-Saclay, qui siège à l’Académie des sciences et étudie la diversification microbienne, indique : « L’uacuterétude me semble correcte, bien faite sur le plan descriptif ». Elle complète ses propos en ces termes : « Ils montrent des images des cellules qui se divisent et ont également séquencé le génome de l’organisme ».
Broader Implications for Astrobiology and Agriculture
Researchers see the find as more than a biological curiosity. Oliverio compared the breakthrough to the historic sub-4-minute mile for runners, which was long thought to be impossible. Once one athlete achieved it, however, it was just weeks before it happened again. Oliverio notes that it provides concrete proof of what is possible for complex cell architecture.
Understanding how these organisms stabilize their cellular membranes and proteins could eventually inform the development of heat-tolerant crops or drugs that remain stable across wider temperature ranges. Beyond terrestrial applications, the research gives astrobiologists a new baseline for understanding the absolute boundaries of life elsewhere in the universe.