For decades, scientists believed that approximately 60 °C marked the thermal limit for eukaryotic life—organisms whose cells have a nucleus and complex internal structures. A tiny amoeba has just shattered that limit.
His name is Incendiamoeba cascadensis, although researchers are already calling it the fire amoeba.
This microorganism can feed, grow, and reproduce at temperatures that would destroy the cells of almost any animal or plant. Experiments have shown that it is able to divide at 63 °C, remains active and on the move at 64 °C and can take on a protective form to survive until 70 °C.
When the temperature drops again, the amoeba emerges from its state of dormancy and resumes its vital functions.
It doesn't just tolerate the heat—it needs it to survive.
She appeared where no one expected to find her
The amoeba was found in a small geothermal stream in Lassen Volcanic National Park, in northern California.
Researchers from Syracuse University had traveled to the park to study another organism capable of living in the hot, extremely acidic waters of Boiling Springs Lake. However, they decided to also collect samples from a seemingly ordinary stream they came across during their trip.
The water in that stream had one significant difference: it had a relatively neutral pH.
Upon returning to the laboratory, the scientists kept the samples at temperatures similar to those at the site. After several days, an unknown amoeba appeared. When they began to increase the heat, the organism did not die.
On the contrary, it continued to grow.
A creature that lives at temperatures between 42 and 63 degrees
The experiments showed that the amoeba begins to reproduce around the 42 °C. Its optimal temperature ranges between 55 and 57 °C, but it can continue to divide into 63 °C, a record for any known eukaryotic organism.
At 64 °C, it no longer reproduces, but it still retains the ability to move. When the water reaches higher temperatures, it forms a cyst that protects the cell.
In that state, it can survive temperatures up to 70 °C and become active again when the right conditions return.
The scientists also found that the amoeba possesses genes related to DNA repair, protein stability, and response to environmental changes. These adaptations could prevent its cellular structures from breaking down under extreme temperatures.
He eats as if he were slurping spaghetti
The amoeba has an extraordinary ability to transform its body.
In its usual form, it moves slowly and wraps its membrane around long, filamentous thermophilic bacteria. It then folds them and gradually absorbs them, in a movement that researchers compare to slurp spaghetti.
It can also take on an elongated, worm-like shape, which allows it to move more quickly. Scientists believe that this transformation could help it escape when water temperatures become unfavorable.
The Search for Extraterrestrial Life Is Changing
The discovery not only sets a new biological record; it also expands the range of environments in which scientists might search for complex life.
Until now, much of the research on organisms capable of living in extreme heat has focused on bacteria and archaea, which are much simpler cells that lack a nucleus.
The fire amoeba demonstrates that a eukaryotic cell can feed, repair its genetic material, move, and reproduce under conditions that were previously considered incompatible with that form of life.
This could influence the exploration of worlds with volcanic or hydrothermal activity. If complex life on Earth can overcome limits that once seemed insurmountable, some extraterrestrial environments might turn out to be less inhospitable than we had assumed.
The existence of this amoeba sends a disturbing and fascinating message: We still don't know the true limits of life.
The news was reported this September 22, 2026, although the discovery had initially been presented as preliminary research in 2025. The new publication explores the mechanisms that make its extraordinary resistance possible.
