Scientists supported by NASA have discovered an organism that can survive extreme temperatures once thought to be impossible for complex life. High heat can destroy essential cellular components, creating a major challenge for cells with complex structures such as a nucleus, which contains sensitive genetic information.

A research team observed an amoeba dividing and multiplying at an astonishing 145 degrees Fahrenheit (63 degrees Celsius) in the hot waters of California’s Lassen Volcanic National Park. The finding sets a record for the highest temperature limit known for any eukaryote.

Incendiamoebae cascadensis, also known as the fire amoeba, stops reproducing when temperatures exceed 145 degrees Fahrenheit (63 degrees Celsius). However, it remains active and continues foraging for food at temperatures up to 147.2 degrees Fahrenheit (64 degrees Celsius).

Several species of fungi and red algae previously held the record for eukaryotic heat tolerance at 140 degrees Fahrenheit (60 degrees Celsius). The new findings were published Tuesday in the journal Cell.

Astrobiologists study the limits of life on Earth to understand how organisms might survive on other worlds, including Mars, where environmental conditions are harsher than those on our planet. Organisms that tolerate extreme temperatures, pH levels, radiation and other challenging conditions are known as extremophiles.

Research on extremophiles helps scientists understand the limits of life as we know it. These organisms also produce unique proteins that could have applications in biotechnology, industry and medicine.

Extremophile research has mainly focused on unicellular bacteria and archaea. The new study shows that eukaryotes—with their more complex cellular structures—may be more durable in extreme environments than previously thought. The discovery could help scientists determine where complex life might survive elsewhere in the universe.

What is a eukaryote?

Life on Earth is divided into two broad categories: prokaryotes and eukaryotes.

Prokaryotes are single-celled organisms that do not have a nucleus or membrane-bound organelles. Because they contain less cellular machinery, they may have fewer components vulnerable to environmental extremes such as intense heat, bitter cold, corrosive acidity and harmful radiation.

Organisms that live in extreme heat are known as thermophiles. To be considered a true heat-loving thermophile, an organism must be able to reproduce, move, feed and survive above 113 degrees Fahrenheit (45 degrees Celsius).

Prokaryotes include bacteria and archaea. Archaea are particularly well known for surviving in extreme environments. Scientists believe that the relative simplicity of prokaryotic cells may have helped them become some of the first forms of life on Earth, billions of years ago, when the planet’s environment was much harsher than it is today.

Eukaryotes are more complex organisms that are thought to have evolved later in Earth’s history. Their cells contain a separate nucleus that protects genetic information, as well as membrane-bound organelles such as mitochondria and the endoplasmic reticulum. These organelles act like tiny cellular machines with specialized functions.

Eukaryotes include organisms ranging from single-celled algae to multicellular plants, animals and humans.

How the fire amoeba survives extreme heat

High temperatures can break down proteins and other biomolecules that cells need to function. Heat can also damage membranes and destroy cells. Scientists had suggested that the membranes surrounding eukaryotic organelles could not remain stable above 144 degrees Fahrenheit (62 degrees Celsius).

The discovery of I. cascadensis challenges that assumption.

“Assumptions about membrane stability may have limited studies in eukaryotes,” says Beryl Rappaport, a graduate student at Syracuse University and lead author of the study. “We hope that the discovery of I. cascadensis will inspire others to continue their search for high-temperature eukaryotes.”

The research team sequenced the amoeba’s genome and studied gene expression at multiple temperatures. The researchers identified genes that help stabilize the amoeba’s DNA and protect it from damage. Other genes allow the organism to sense changes in its external environment.

Exposure to high temperatures also increased the expression of genes involved in maintaining proper protein folding, an important process for keeping proteins functional under stressful conditions.

“We were able to discover a number of strategies that help I. cascadensis survive at high temperatures, and some of these strategies may be used by thermophiles in all organisms,” Rappaport says. “For example, some proteins in I. cascadensis have high positive surface charges that help maintain stability. The charges on these proteins are similar to those found in thermophilic bacteria and archaea.”

The researchers also compared the amoeba’s genetic information with data from studies conducted around the world. They found similar pieces of DNA in geothermal samples from locations including New Zealand and Yellowstone National Park.

The findings suggest that other heat-tolerant amoebae related to I. cascadensis may live in geothermal environments around the world.

What the discovery means for the search for life beyond Earth

Earth is the only planet known to support life. For life as we know it to survive elsewhere in the solar system or beyond, organisms may need to withstand conditions very different from those found on Earth.

“Studying extremophiles helps us better understand the biochemical and physiological limits of life as we know it on Earth,” says Alison Olcott, an astrobiology program scientist at NASA Headquarters in Washington. “This information guides NASA’s search for life because it expands the range of conditions under which life may exist elsewhere.”

The research improves scientists’ understanding of how complex cellular life persists in extreme environments on Earth—and where similar life might survive beyond our planet.

“Finding eukaryotes that survive in high-temperature environments not only expands our understanding of where life is found, but also how complex that life is,” Olcott says.

However, survival depends on more than temperature. Organisms also require the right combination of acidity, oxygen levels, pressure, water and food.

“While it may certainly be possible for complex life like I. cascadensis to survive on other planets, Earth is currently the only planet that we know of that has all the requirements for I. cascadensis to be happy,” Rappaport says. “Temperature is not the only issue; the environment also needs proper acidity, oxygen levels, pressure, water and food. I. cascadensis cannot survive on its own; it needs the support of other life as well.”

By revealing that a complex organism can reproduce at 145 degrees Fahrenheit, the discovery expands scientists’ understanding of life’s ability to withstand extreme heat—and gives astrobiologists another clue about where complex life might exist in the universe.