Scientists have found an amoeba in a California hot spring that reproduces at 145 degrees Fahrenheit (63 degrees Celsius), the highest temperature recorded for a eukaryote, the group of organisms whose cells have a nucleus. The previous record was 140 degrees Fahrenheit (60 degrees Celsius).
Researchers led by H. Beryl Rappaport of Syracuse University named the organism Incendiamoeba cascadensis, the “fire amoeba.” They described it Sept. 22 in the journal Cell, according to NASA, which helped fund the work. The paper is titled “A geothermal amoeba sets a new upper temperature limit for eukaryotes,” according to StudyFinds. Angela Oliverio, a microbial ecologist at Syracuse, is the corresponding author. Live Science called Rappaport a microbiologist, while NASA described her as a graduate student.
Where the Fire Amoeba Lives
The organism came from a tributary of Hot Springs Creek in Lassen Volcanic National Park in California, according to Live Science. The team collected water, sediment and mineral buildup at 20 sites over three years, StudyFinds reported. EurekAlert’s release put the field temperatures at 47 to 64 degrees Celsius. StudyFinds gave the range as 120 to 149 degrees Fahrenheit, which is about 49 to 65 degrees Celsius. StudyFinds said the water was near neutral in acidity.
Genetic signatures matching the amoeba turned up in a geothermal mat in New Zealand and at Yellowstone National Park, according to Sci.News, so the organism may not be limited to one spring.
How the Researchers Tested the Heat Limit
The team grew the amoeba in the laboratory on bacteria fed with wheat berries, StudyFinds reported. It took one to two weeks for the amoebas to colonize a dish at 135 to 140 degrees Fahrenheit and three weeks at 145 degrees. The researchers tracked growth over one-week periods at 17 temperatures from 86 to 147 degrees Fahrenheit. Growth stopped below about 108 degrees Fahrenheit (42 degrees Celsius) and peaked at 131 to 135 degrees (55 to 57 degrees Celsius), StudyFinds said.
Microscopy showed the cells dividing by mitosis at 63 degrees Celsius. Cells kept moving up to 64 degrees Celsius, NASA said. Live Science reported that cells survived five minutes at 70 degrees Celsius in a cyst-like state and recovered afterward, and that 80 degrees Celsius killed them. StudyFinds said the cells alternate between an elongated form and a compact form about every 90 seconds. Rappaport told Live Science she was surprised by the result and that her team went back to check that the incubators were calibrated correctly.
The Heat Record in Numbers
The new record is 3 degrees Celsius above the old one, an increase of 5%. The amoeba’s death point sits well above its reproduction ceiling: 80 degrees Celsius kills it, 17 degrees above the 63 degrees at which it divides. That margin is nearly six times the size of the record’s increase.
Fungi and red algae held the previous eukaryote record of about 60 degrees Celsius, according to Sci.News. StudyFinds said that record had stood since the 1970s. The previous amoeba record was about 57 degrees Celsius, held by Echinamoeba thermarum, Sci.News reported. Prokaryotes live at much higher temperatures. The archaeon Methanopyrus kandleri grows at 122 degrees Celsius, or 252 degrees Fahrenheit, Live Science reported. That is nearly twice the fire amoeba’s 63 degrees.
How the Fire Amoeba Tolerates the Heat
The researchers sequenced the amoeba’s genome and compared it with three cooler-living amoebas. A close relative, Vermamoeba vermiformis, lives in water heaters and tolerates less heat, according to Sci.News and StudyFinds. The fire amoeba carries extra genes for protein maintenance and DNA repair, StudyFinds reported. Its proteins have few sticky patches on their surfaces that can make proteins clump together in heat, and they carry a high positive surface charge.
StudyFinds said about five times as many of its proteins are predicted to stay stable above 140 degrees Fahrenheit as in its cooler relatives. The role of cell membranes, the question researchers have long raised about heat and complex cells, remains unresolved. Rappaport said in NASA’s release that studies of eukaryotes may have been limited by assumptions about membrane stability.
StudyFinds listed limits to the work: the organism cannot be genetically manipulated, the protein melting points are computer predictions, and gene activity was compared at only two temperatures. Debashish Bhattacharya, an evolutionary biologist at Rutgers University who was not involved in the study, told Live Science that eukaryotes cannot simply grab a batch of genes the way bacteria do.
What Researchers Plan Next
“This finding pushes the bounds of what we thought was possible,” Oliverio said in the EurekAlert release. NASA said the result expands the range of conditions where scientists think life could exist elsewhere. Rappaport told NASA she hopes the discovery encourages others to keep searching for high-temperature eukaryotes, and she told Live Science she plans to study the amoeba’s closest relatives.
Funders include NASA’s Exobiology program, the National Science Foundation, the National Institutes of Health, the Howard Hughes Medical Institute, the Alfred P. Sloan Foundation and Syracuse University, StudyFinds reported. The paper’s digital object identifier is 10.1016/j.cell.2026.08.043.
