A single-celled amoeba cultured from a hot stream in California's Lassen Volcanic National Park can divide at 145 degrees Fahrenheit (63 degrees Celsius), the highest temperature at which any eukaryote is known to reproduce. The finding was published in the journal Cell by a Syracuse University-led team on September 22, 2026.

The organism, named Incendiamoeba cascadensis, or "fire amoeba from the Cascades," belongs to the eukaryotes, the branch of life whose cells keep their DNA inside a nucleus. That branch includes fungi, plants, and animals, including people. Until now, the accepted upper limit for eukaryotic growth was about 140°F (60°C), a mark held by a few fungi and red algae.

The result matters because it corrects a working assumption in biology about how much heat complex cells can tolerate. It also widens the range of conditions astrobiologists consider when they ask where complex life might persist.

A Few Degrees That Move a Long-Held Limit

According to NASA's summary of the research, the fire amoeba stops reproducing above 145°F but keeps moving and searching for food at up to 147°F (64°C). In the lab, it remained partially active at 150.8°F (66°C) and recovered after five minutes at 158°F (70°C), surviving by entering a dormant state. Exposure to 176°F (80°C) killed it.

Simpler microbes tolerate far more heat. According to Science News, the archaeon Methanopyrus kandleri holds the record for all life, growing at about 252°F (122°C). Heat is a particular problem for eukaryotes, however, because their nucleus and internal compartments depend on membranes that can break apart as temperatures rise.

Scientists had suggested that the membranes around those compartments could not remain stable above about 144°F (62°C). NASA said the discovery of the fire amoeba proves that assumption wrong.

Corresponding author Angela Oliverio, a microbiologist at Syracuse University, compared the result to the first sub-four-minute mile in an interview with NPR. What mattered, she said, was less the size of the gain than "the proof that it was possible."

Sampling Lassen's Steaming Streams

Lead author Beryl Rappaport and colleagues collected water from geothermal sites in the park between 2023 and 2025. One sampling site was a tributary of Hot Springs Creek that Oliverio described to NPR as easy to overlook because of the tall vegetation around it. According to the team's earlier preprint, the amoeba turned up at 14 of the 20 locations sampled.

In the lab, the researchers spotted an amoeba growing at 135°F (57°C), the previous record for any amoeba, and kept raising the incubator temperature. The organism continued to divide until it reached 145°F. The preprint also reported that it did not grow below about 108°F (42°C), making it an obligate thermophile that requires heat to thrive.

Lassen Volcanic National Park is the southernmost active volcanic region in the Cascade Range, and its centerpiece, Lassen Peak, is the world's largest plug dome volcano. Water heated by hot or molten rock beneath the peak feeds boiling pools, mud pots, and steam vents at sites such as Bumpass Hell and Sulphur Works.

The fire amoeba does not survive on heat tolerance alone. It feeds on bacteria, and Rappaport told NASA it could not live on its own. She said a suitable habitat also needs the right acidity, oxygen levels, pressure, water, and food.

The team also searched genetic data from other studies and found similar DNA in geothermal samples from New Zealand and Yellowstone National Park. That suggests related heat-loving amoebas may live in hot springs elsewhere, though DNA fragments alone do not reveal how much heat those organisms can withstand.

Genes Built for Heat

After sequencing the amoeba's genome, the researchers found many genes that help stabilize and protect DNA and others that let the organism sense its surroundings. At high temperatures, the amoeba increased the activity of genes involved in keeping proteins correctly folded.

Rappaport told NASA that some of the amoeba's proteins carry a strong positive surface charge, a trait also seen in heat-loving bacteria and archaea. She added that the team hopes the discovery "encourages others to keep searching for high temperature eukaryotes."

That toolkit is part of why NASA, which helped fund the work, is interested. Alison Olcott, program scientist for Exobiology at NASA Headquarters, said studies of extremophiles help define the range of conditions scientists consider when searching for life elsewhere. NASA also noted that proteins from extremophiles have potential uses in biotechnology, from industry to medicine.

What the Study Shows and What It Does Not

The findings first circulated in November 2025 as a preprint on bioRxiv, a server for studies that have not yet undergone peer review. The September 2026 publication in Cell means the work has now passed that review, which is the new development in this story.

This is a laboratory culture study built on field samples from one national park. It establishes that one species can divide at 145°F under controlled conditions. It does not show how common such organisms are, whether relatives in Yellowstone or New Zealand share the same limit, or how the amoeba fares in the wild as water temperatures fluctuate.

The study also does not show that complex life exists beyond Earth. Rappaport said it could be possible for an organism like the fire amoeba to survive on another planet, but that Earth is the only planet currently known to meet all of its needs, and temperature is only one of them. The research examined heat tolerance and did not assess any effect on human health.

Visiting Lassen's Thermal Areas Safely

The discovery may draw fresh attention to Lassen's hydrothermal features, and the National Park Service is clear about the risks. It says traveling off trail or entering water in hydrothermal areas is both dangerous and unlawful. Ground that looks solid can be a crust hiding acidic, boiling water or mud, and visitors who stepped off trails at Devils Kitchen and Sulphur Works have suffered severe burns.

The park advises staying on trails and boardwalks, keeping young children close, and never touching thermal water, which can damage skin and lungs even when it is not hot enough to burn. Bumpass Hell, the park's largest hydrothermal area, is reachable by trail only in summer and fall, roughly June through October, so visitors should check current conditions before traveling.

The research team plans to keep searching hot springs for other heat-tolerant eukaryotes. For now, the fire amoeba holds the confirmed record, and the next question is whether its relatives can be isolated and tested the same way.

What Readers Want to Know

What did scientists discover in Lassen Volcanic National Park?

Researchers described a new amoeba species, Incendiamoeba cascadensis, that can divide at 145°F (63°C). That is the highest temperature at which any eukaryote, an organism whose cells have a nucleus, is known to reproduce.

How much higher is this than the previous record?

The earlier limit for eukaryotes was about 140°F (60°C), held by some fungi and red algae. The fire amoeba exceeds it by about 3°C, or roughly 5°F.

How much heat can it survive without reproducing?

In lab tests, it stayed active at up to 147°F (64°C), survived five minutes at 158°F (70°C) in a dormant state, and died at 176°F (80°C).

Is this research new?

The findings first appeared as a preprint in November 2025. The peer-reviewed version was published in Cell on September 22, 2026.

Does the fire amoeba pose a risk to people?

The study examined heat tolerance and did not assess human health effects. Park rules already prohibit entering hydrothermal water because it can be scalding and acidic.

Does this mean complex life could exist on other planets?

Not on its own. The researchers note that the amoeba also needs specific acidity, oxygen, pressure, water, and other living organisms, and Earth is the only planet known to provide all of them.

What comes next for the research?

The team plans to search other hot springs for heat-loving eukaryotes. Similar DNA has already been detected in geothermal samples from Yellowstone and New Zealand.