Heat-loving amoeba shatters temperature ceiling for complex organisms
A newly discovered amoeba species, Incendiamoeba cascadensis, thrives in geothermal waters up to 70°C, with feeding and reproduction possible at 63°C. This exceeds the previous 60°C threshold thought to limit eukaryotic life, which includes all organisms with nucleated cells. Researchers collected the microbe from a hot spring in California's Lassen Volcanic National Park, where it acts as a top predator on thermophilic bacteria.
The fire amoeba measures roughly 40 micrometres in length, over ten times larger than a typical bacterium and comparable in width to a human white blood cell. Within its geothermal habitat, it acts as an apex predator, consuming thermophilic bacteria that are far more abundant in the hot spring environment.
Laboratory testing across seventeen temperature points showed no growth below 40°C or above 63°C, with peak performance between 55 and 57°C. Above 64°C, the amoeba forms a protective cyst, though these become inactivated beyond 70°C. Genetic database searches have found similar RNA signatures in New Zealand's Taupō Volcanic Zone and three Yellowstone locations, suggesting related species may exist elsewhere.
The discovery could reshape scientific understanding of where complex life can exist, potentially influencing how researchers approach questions about life on other planets or in extreme Earth environments. It may also prompt revisions to biology curricula, as the previous 60°C ceiling for eukaryotes has been taught as a firm boundary. Industries relying on heat-tolerant organisms, such as biotechnology and waste treatment, could eventually explore applications, though such developments remain speculative at this stage.