PSU virologists help discover record-breaking organism at Lassen Volcanic National Park

For more than 20 years, Portland State virologist Ken Stedman has led his lab on annual trips to California's Lassen Volcanic National Park to sample the hot, acidic environments created by volcanic activity. There, his team hunts for viruses that can help answer fundamental questions about virus evolution, life on Earth and even life beyond Earth.

But during a recent trip, Stedman's team collaborated on a discovery that challenged previous assumptions. They found an organism that lives at extreme temperatures previously thought impossible for complex life.

"It is pretty amazing that our colleagues found this record-breaking amoeba in a stream that we always just walk past on our way to our sampling sites," said Stedman, a professor of biology at PSU. "We are so glad to have been able to enable their work."

Organisms that endure at the edges of habitability under extreme temperature, pH, radiation and other environmental conditions are known as extremophiles. While most of this research has focused on single-celled bacteria and archaea - the latter of which is a primary focus of Stedman's lab - far less is known about how eukaryotic life responds to extreme heat.

To explore that limit, Syracuse researchers Angela Oliverio and Beryl Rappaport joined Stedman, PSU research associate Ignacio de la Higuera and other collaborators at Lassen. The park's chemically diverse, high-temperature geothermal springs make 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.

"This just goes to show how much more there is to discover," Stedman said.

Back at Syracuse, researchers tested the organism's limits in the lab. 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 moving. At 70°C (158°F), they formed cysts, dormant structures that can survive the extreme conditions and reactivate when temperatures cool.

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," Oliverio said. That includes extreme environments on Earth and potentially other planets.

The findings were published in the journal Cell. Stedman and de la Higuera are co-authors on the paper.

Adapted from news materials provided by Syracuse University.