Record-breaking Heat-resistant 'Fire Amoeba'

A newly identified single-celled organism thriving in the hot waters of California's Lassen Volcanic National Park has broken records for heat tolerance. Named Incendiamoeba cascadensis meaning "fire amoeba from the Cascades" this organism can grow and divide at temperatures up to 63C (145F), the highest known for any eukaryotic lifeform. Remarkably, it requires temperatures of at least 42C to begin growth, classifying it as an obligate thermophile.

According to biologists H. Beryl Rappaport and Angela Oliverio of Syracuse University, "Our findings challenge the current understanding of thermal limits for eukaryotic cells and expand knowledge of the environments in which eukaryotic life can exist."

Most life on Earth thrives near 20C, but extremophiles have adapted to environments far beyond these norms, from hydrothermal vents to acidic pools and arid deserts. While most extremophiles are prokaryotessimpler organisms like bacteria and archaeaeukaryotes such as I. cascadensis are more fragile, containing nuclei and complex organelles that are easily disrupted by heat.

I. cascadensis was collected from hot springs in Lassen National Park between 2023 and 2025. Researchers successfully cultured samples in flasks at temperatures ranging from 30C to 64C, feeding the amoebae with bacteria to observe their growth. The amoeba did not grow below 42C, while optimal growth occurred between 55C and 57C. Cell division was observed at 58C and 63C, and the organism remained active even at 64C, surpassing the previous record of 57C for amoebae.

When temperatures reached 66C, I. cascadensis formed protective cysts to survive extreme conditions. Surprisingly, it also formed cysts at 25C, a high lower limit for eukaryotic organisms. The amoeba stopped moving at 70C but could revive when cooled, only ceasing activity permanently at 80C.

Genomic analysis revealed adaptations for rapid signaling, heat-response mechanisms, and an expanded array of heat-resistant proteins and chaperones. Similar DNA sequences were detected in environmental samples from Yellowstone National Park and New Zealand's Taup Volcanic Zone, suggesting that I. cascadensis may be more widespread.

This discovery indicates that eukaryotic life can endure far higher temperatures than previously believed, offering insights into the potential habitability of extreme environments, including extraterrestrial worlds. "Incendiamoeba cascadensis thrives at temperatures previously thought impossible for any eukaryotic organism, raising new questions about thermal limits in eukaryotic cells," the researchers noted.

The full study has been shared as a preprint on bioRxiv.

Author: Sophia Brooks