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NASA-Supported Scientists Discover an Amoeba That Thrives in Record Heat

Scientists supported by NASA have discovered a complex organism that can survive temperatures once thought impossible for eukaryotic life. The amoeba, found in the hot waters of California’s Lassen Volcanic National Park, can reproduce at 145 degrees Fahrenheit (63 degrees Celsius)—the highest temperature ever recorded for a known 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 degrees Fahrenheit (64 degrees Celsius). The previous eukaryote temperature limit, 140 degrees Fahrenheit (60 degrees Celsius), was held by several species of fungi and red algae. The findings were published Tuesday in Cell.

How the fire amoeba survives extreme heat

High temperatures can destroy proteins, membranes, and other essential cellular components. This creates a major challenge for eukaryotic cells, which contain complex structures such as a nucleus filled with sensitive genetic information.

It had been 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 Rapaport, 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 examined gene expression at multiple temperatures. They identified genes that help stabilize its DNA and protect it from damage. Other genes allow the organism to sense changes in its environment.

High temperatures also increased the activity of genes involved in maintaining proper protein folding. Some proteins in I. cascadensis have highly positive surface charges that may help them remain stable. Similar protein characteristics have been observed in heat-loving bacteria and archaea.

What are extremophiles?

Organisms that tolerate extreme temperatures, pH levels, radiation, or other harsh environmental conditions are known as extremophiles. Those that live in extreme heat are called 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).

Extremophile research has traditionally focused on unicellular bacteria and archaea. Prokaryotes lack a nucleus and membrane-bound organelles, leaving fewer complex cellular structures vulnerable to intense heat, extreme cold, corrosive acidity, or harmful radiation.

Archaea are particularly capable of surviving extreme conditions. Because of their relative simplicity, scientists believe prokaryotes may have been among the first forms of life to appear on Earth, billions of years ago, when the planet’s environment was harsher than it is today.

Why this discovery matters for the search for life

Eukaryotes are more complex organisms that evolved later in Earth’s history. They contain a nucleus as well as membrane-bound organelles, including mitochondria and the endoplasmic reticulum. Eukaryotes range from single-celled algae to plants, animals, and humans.

The discovery of I. cascadensis shows that complex cells may be more resilient than previously thought. It could help scientists better understand where complex life might survive on Earth and elsewhere in the universe.

Researchers also compared genetic data from studies around the world. They found similar DNA sequences in geothermal samples from locations including New Zealand and Yellowstone National Park. The results suggest that other heat-tolerant amoebae related to I. cascadensis may be living in geothermal environments around the world.

Astrobiologists study the limits of life on Earth to explore how organisms might survive on other worlds, including Mars, where conditions are more challenging than those on our planet. Extremophiles also produce unique proteins that could have applications in biotechnology, industry, and medicine.

“Studying extremophiles helps us better understand the biochemical and physiological limits of life as we know it on Earth,” says Alison Olcott, 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.”

Heat is only one requirement for life

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 environmental conditions far different from those found on Earth.

However, researchers emphasize that temperature is only one part of a larger ecosystem. Life also requires suitable 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,” Rapaport 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.”

The finding expands scientists’ understanding of both the temperature limits of complex life and the environments that could potentially support life beyond Earth.

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