‘Fire amoeba’ breaks record for hottest temperature at which complex life can grow

A newly discovered amoeba can grow and divide at temperatures up to 145 degrees Fahrenheit (63 degrees Celsius), setting a record for the highest temperature at which complex life is known to thrive.

The heat-loving organism, found in California’s Lassen Volcanic National Park, can also survive for short periods at temperatures as high as 158 F (70 C), according to a new study. Before this discovery, no complex cells were known to replicate above 140 F (60 C).

Amoeba surprises scientists with extreme heat tolerance

“I was very surprised,” study lead author Beryl Rappaport, a microbiologist at Syracuse University in New York, told Live Science. “I had to make sure to go back and check the incubator to make sure it was calibrated correctly. It was really great.”

Amoebae are single-celled organisms that move by extending tendrils of cell fluid. They are eukaryotes, meaning their DNA is enclosed inside a nucleus surrounded by a membrane.

Although amoebae are not plants, animals or fungi, they are more complex than prokaryotes such as bacteria and archaea, which do not have a nucleus.

‘Fire amoeba’ found in a volcanic park

Rappaport and her colleagues collected samples from a tributary of Hot Springs Creek in Lassen Volcanic National Park. The researchers suspected that geothermal springs might contain amoebae capable of surviving extreme heat, but relatively few of these organisms have been studied in the laboratory.

They named the newly identified species Incendiamoebae cascadensis, meaning “fire amoeba from the Cascades.” The amoeba thrives at temperatures between 131 and 135 F (55 and 57 C), and it stopped growing below 108 F (42 C).

How hot can the record-breaking amoeba get?

Using a heating microscope to keep the cells warm, the researchers observed I. cascadensis dividing at temperatures as high as 145 F (63 C). That is the highest temperature known to support replication in a eukaryotic cell.

At 158 F (70 C), the amoeba formed a protective shell and entered a dormant state. When researchers held the cells at that temperature for five minutes and then lowered the temperature to 140 F (60 C), the amoebae recovered.

However, the organisms could not survive heating to 176 F (80 C). Some bacteria and archaea, known as prokaryotes, can withstand even higher temperatures, with some surviving temperatures of up to 250 F (122 C).

Heat-resistant proteins may hold the key

The researchers found that proteins in I. cascadensis have positively charged amino acids on their surfaces. Heat-loving prokaryotes have similar characteristics, and the adaptation may help stabilize proteins at high temperatures.

Other specialized eukaryotes can also survive extreme heat. Some fungi, for example, can withstand temperatures up to 140 F (60 C) in the desert. However, these temperatures remain lower than those tolerated by certain bacteria and archaea.

Why can some cells survive extreme heat?

The difference in heat tolerance between prokaryotes and eukaryotes may partly result from how quickly they can adapt genetically to heat stress.

“Once it becomes a bacterium, you can scoop it up and replace its genome” with DNA from other prokaryotes, evolutionary biologist Debashish Bhattacharya of Rutgers University, who was not involved in the study, told Live Science. This ability allows prokaryotes to adapt relatively quickly to stressful environments.

In eukaryotes, DNA is enclosed inside the nucleus. As a result, “eukaryotes can’t just acquire large amounts of genes and switch lifestyles at the same rate as prokaryotes,” Bhattacharya said. “It takes much more evolutionary changes to turn eukaryotes into extremophiles.”

Could complex life exist beyond Earth?

In future research, Rappaport plans to study Incendiamoebae and its closest relatives to learn how they evolved to tolerate extreme heat.

Understanding these adaptations could help scientists define the limits of life on Earth—and assess whether complex life might exist elsewhere in the universe.

The researchers reported their findings in the journal Science on Tuesday, September 22.