A new one has been discovered thermophilic amoeba named Let’s set fire toeba cascadensis (“fire amoeba of the Cascades“), isolated in the warm waters of Lassen Volcanic National Park (California, USA). This microorganism is capable of replicating up to a temperature of 63°Cexceeding the previously hypothesized upper limit for eukaryotic life. The finding is reported in an ongoing study pre-primt (not yet peer-reviewed) published November 24. To understand the significance of the news, we need to take a step back and distinguish the two great domains of life. The eukaryotes they include animals, plants, fungi and protozoa such as amoebae and have complex cells, with a nucleus that houses the DNA and internal organelles (such as mitochondria) enclosed by membranes. They are complex organisms and our human cells, for example, struggle to resist even above 43°C. While prokaryotes are simpler organisms, with free DNA in the cytoplasm and include bacteria and archaea, including many extremophiles capable of living in extreme conditions.
The Californian park that is home to the dormant volcano Lassen Peakis full of bubbling mud pools and hot springs, the ideal habitat for these microorganisms. The amoeba was isolated in 14 out of 20 samples from a thermal stream (with temperatures between 49 and 65 °C and neutral pH) between 2023 and 2025. This is a obligate extremophiledoes not grow under i 40°C and has optimal growth temperature at 55 – 57 °C. It manages to divide up to 63°C and to move to 64°C. Also to 70°Cthe cells formed dormant “cysts” capable of reactivating at lower temperatures. 80 °C instead represents the maximum limit beyond which the organism is unable to survive and recover. This heat tolerance could be made possible by the presence of thermostable proteins, such as gli molecular chaperones and the Heat Shock Proteins (HSP), essential for managing thermal stress.
Before this discovery, the maximum temperature limit for the growth of eukaryotes was set at 60°Ca threshold reached only by some species mushroomshow Chaetomium thermophilumand red algae. Among amoebae, the previous record belonged to Echinamoeba thermarumcapable of growing up to 57°C. For comparison with i limits of prokaryotic life (bacteria and archaea), there are organisms capable of living at much higher temperatures, such as the bacterium Geothermobacterium ferrireducens which grows up to 100°C and the archaeum Methanopyrus kandleri which even survives 122°C.
DNA analysis has shown that the new species is related to Vermamoeba vermiformisa common amoeba which however only lives up to 40-45°C. Genetic sequences attributable to those of I. cascadensis they have also been found in New Zealand and in Yellowstone Park, suggesting that this microorganism has a global spread in geothermal areas. In its environment, the “fire amoeba” feeds on thermophilic bacteria (as Meiothermus ruber) and presents two distinct morphologies: one “vermiform“elongated and one”amoebiform“more compact.
The discovery of I. cascadensis thus moves this biological boundary forward and could help understand important biological mechanisms used to adapt to these temperatures. Studying its thermostable enzymes and systems that prevent protein aggregation at high temperatures could open new avenues for biotechnological applications.
