New ‘fire amoeba’ shatters heat record for complex life

Scientists have discovered a new species of amoeba that thrives at temperatures previously thought impossible for complex life, breaking the long-standing record for eukaryotic heat tolerance. The organism, named Incendiamoeba cascadensis — or "fire amoeba from the Cascades" — can actively grow and divide at 63°C (145°F) and survive temperatures up to 70°C (158°F), according to a study published Tuesday in the journal Cell.the-scientist+1

A Record-Breaker From California's Hot Springs

For more than five decades, researchers had pegged 60°C as the upper temperature limit for eukaryotes — organisms with complex cells, including animals, plants, fungi, and some microbes. Angela Oliverio, a microbial ecologist at Syracuse University, and her team upended that assumption after collecting samples from geothermal streams in Lassen Volcanic National Park in California's Cascade Range between 2023 and 2025, where water temperatures ranged from about 47°C to 64°C.ashleycountyledger+1

One previously unknown amoeba stood out. It grew "robustly" at 57°C in the lab, already matching the highest temperature previously known for amoeba growth. When the researchers kept raising the heat, the organism continued dividing at 63°C — three degrees above the supposed eukaryotic ceiling. At 64°C, the amoeba encased itself in a protective cyst, but it could resume normal activity after exposure to temperatures as high as 70°C.the-scientist+1

Convergent Evolution Under Extreme Heat

Genome sequencing revealed that I. cascadensis possesses 6,919 genes unique to it, with enriched pathways for heat shock proteins, calcium signaling, DNA repair, and protein maintenance compared to related species living in milder environments. The amoeba's proteins also feature more positively charged amino acids on their surfaces, a trait shared with some of the most heat-tolerant bacteria and archaea, suggesting convergent evolution across vastly different branches of life.the-scientist+1

"Even though these organisms are so different, there's convergence in how protein properties are selected for stability under high temperatures," said study first author Beryl Rappaport, a doctoral student at Syracuse University.ashleycountyledger

Pushing the Boundaries

The discovery, while only a few degrees beyond the previous record, carries broader implications for astrobiology, biotechnology, and how scientists search for life in extreme environments. The amoeba's heat-stable proteins could find applications in industrial and biotechnological processes.the-scientist

"Every time we set a new world record in sports, it's amazing and celebrated, even if it's by milliseconds," Oliverio said. "We should do the same for amoebae. These very small changes expand our understanding of what we think is possible."ashleycountyledger