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Volcano "Fire Amoeba" Sets New Heat Record — Hottest-Known Eukaryote

08:22 PM, 12/02/2025
Volcano "Fire Amoeba" Sets New Heat Record — Hottest-Known Eukaryote

Researchers have identified Incendiamoeba casadensis, nicknamed the "fire amoeba," in Lassen hot springs; it grows and divides at temperatures up to 145°F and begins growing only above about 107°F. Lab tests across 17 temperatures showed the amoeba forms dormant cysts near 151°F and becomes nonviable around 176°F. Genomic analysis reveals expanded heat-shock, protein-repair and DNA-repair systems that likely enable its extreme tolerance. The discovery broadens our view of the thermal limits for eukaryotic life.

A newly described single-celled organism, nicknamed the "fire amoeba of the Cascades," appears to be the most heat-tolerant eukaryotic lifeform yet documented. Researchers discovered Incendiamoeba casadensis in hot springs at Lassen Volcanic National Park and found that it grows and divides at temperatures up to 145°F (63°C).

Discovery and laboratory tests

Scientists collected samples from the hot springs and cultured the organisms across 17 temperature conditions, ranging from 86°F to 147°F (30°C to 64°C). The amoeba showed no growth until ambient temperatures rose above roughly 107°F (42°C), then actively grew and reproduced up to about 145°F. Above that range the organisms showed stress responses: near 151°F (66°C) they formed protective cysts and entered dormancy, and by roughly 176°F (80°C) they lost viability.

Genomic basis for heat tolerance

Genomic analysis offers clues to how this eukaryote copes with extreme heat. The genome contains expanded quality-control and repair pathways, including proteins associated with sustained heat-shock responses, additional enzymes that break down damaged proteins, and an increased complement of DNA-repair and environmental-sensing genes. These features likely help preserve cellular structures—such as nuclei and organelles—that are typically vulnerable to high temperatures.

Why this matters

The findings, reported in a recent preprint, challenge long-standing ideas about the temperature limits of complex life and expand our understanding of where eukaryotes can survive. Historically, extreme-heat niches were thought to be dominated by prokaryotes (bacteria and archaea). The discovery of Incendiamoeba casadensis suggests that eukaryotes can evolve robust mechanisms for thriving in much hotter environments than previously appreciated.

Researchers note that other thermophilic amoebas may still be awaiting discovery, so this species' record might not be permanent. Continued exploration of extreme habitats and further genomic studies should clarify how widespread such adaptations are and what they reveal about life's limits.

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