Record-breaking ‘fire amoeba’ can thrive at 145°F

Biologists have discovered a record-breaking “fire amoeba” that thrives at 63°C (145°F), rewriting the rules for complex cells.

For decades, scientists have relied on a simple rule of thumb: temperatures above 60°C (140°F) should prevent complex cells from surviving. The newly discovered heat-loving amoeba is now challenging that assumption.

Microbiologists have long studied extreme environments to understand “how life can survive at the edges of its limits,” says biologist Angela Oliverio, an assistant professor at Syracuse University and a coauthor of the recent Cell study documenting the newly discovered organism.

This fundamental question, she notes, “helps inform our search for how life might exist elsewhere in the universe.”

Most of this research has focused on bacteria and archaea, which lack nuclei and the complex internal structures found in eukaryotic cells. Far less is known about how eukaryotic life responds to extreme heat.

That question led Oliverio and Beryl Rappaport, a PhD candidate in her lab, to California’s Lassen Volcanic National Park. There, they sampled geothermal sites with collaborators Gordon Wolfe of Chico State and Ken Stedman of Portland State University. Lassen hosts a wide range of chemically diverse, high-temperature geothermal springs, making it an ideal natural laboratory for probing the limits of life. But the team did not find the record-breaking amoeba in one of the park’s famous acidic pools. Instead, it was recovered from an unremarkable-looking tributary. Their discovery underscores how much life may remain hidden in Earth’s extreme habitats.

Fieldwork at Lassen was no walk in the park. Its geothermal areas contain scorching geothermal pools and unstable ground.

“Since we’re sampling from really high-temperature environments, we had to take a lot of safety precautions,” says Rappaport, the study’s lead author.

The team relied on extra-long sampling tools to maintain a safe distance from boiling water and fragile terrain. And in the narrow tributary where the fire amoeba was ultimately discovered, the team even traded standard equipment for makeshift solutions, using barbecue tongs to collect samples in the tight confines of the stream.

Turning up the heat

After bringing samples back to Syracuse, the team began raising the temperature in their incubators. The amoebae continued to grow as temperatures increased from 57°C to 60°C. They kept dividing at 63°C (145°F), setting a new record for eukaryotic life. At 64°C, they were still motile. At 70°C (158°F), they formed cysts, dormant structures that can survive the extreme conditions and reactivate when temperatures cool.

Biologists previously theorized that eukaryotic membranes could not remain stable above roughly 60°C (140°F). This new organism, which they’ve named Incendiamoeba cascadensis, Latin for ‘fire amoeba from the cascades’, reflects both its heat tolerance and the region where it was discovered.

“What we thought was true is not,” Oliverio says, emphasizing how the new data expands the realm of what is biologically possible. She adds that many more heat-tolerant eukaryotes may remain undiscovered.

Understanding the thermal limits of life can help scientists narrow the search for life beyond Earth. Temperature, pH and pressure all place physical constraints on where organisms can survive.

“By expanding the known thermal range for complex life, the discovery opens new possibilities for where eukaryotes might exist,” says Oliverio. That includes extreme environments on Earth and potentially other planets.

Looking ahead

The implications extend beyond astrobiology. The organism may offer new insights for biotechnology. Cellular adaptations that help membranes and proteins may eventually inform the development of thermostable enzymes, more resilient biomaterials, or high-temperature bioprocesses. Current genomics and sequencing technologies make it possible to investigate these adaptations in ways that were far more difficult just two decades ago.

The research also extends beyond Incendiamoeba. Using the same culturing techniques, members of the Oliverio lab are discovering additional extreme microbes, even on campus. Undergraduate students are investigating how similar heat-loving organisms colonize human-made environments.

One case study focuses on a steam pipe on SUNY College of Environmental Science and Forestry’s campus. By collecting samples from high-temperature soils and surfaces exposed to steam, then culturing the microbes they find, students are learning that extreme microbes aren’t confined to hot springs or deep-sea vents. They can also thrive in unexpected human-made environments.

For Rappaport, part of the thrill comes from seeing something entirely new under the microscope. She recalls the first time the amoebae crawled across the flask. “Seeing organisms that maybe no one has seen before is just an incredible feeling,” she says.

Oliverio sees the discovery as a reminder that the boundaries of life are not always where scientists expect them to be. “We should expand our search,” she says.

This research was supported by the National Science Foundation, NASA, the American Physical Society, the National Institutes of Health, the Howard Hughes Medical Institute, the Water and Life Interface Institute, the Alfred P. Sloan Foundation, Syracuse University, the European Commission, the European Molecular Biology Laboratory, the Swiss National Science Foundation, the Gordon and Betty Moore Foundation, and the US Department of Energy Office of Science.

Source: Syracuse University