A tiny amoeba discovered in hot springs raises by several degrees the maximum known temperature for life with cells containing a nucleus.
Its name is Incendiamoeba cascadensis. Researchers isolated it from geothermal waters in Lassen Volcanic National Park, California. This amoeba belongs to the eukaryotes, the vast group that includes animals, plants and fungi. Their common feature is a cell whose genetic material is enclosed within a nucleus.
Boiling Springs Lake, a geothermal area in Lassen Volcanic National Park, California. Credit: Frank Schulenburg, CC BY-SA 4.0.
Image Wikimedia
Until now, a few fungi and red algae could still multiply at around 60 °C. The newcomer exceeds that limit. In the laboratory, researchers observed it multiplying at temperatures up to 63 °C. They even directly observed mitosis, the stage when a cell distributes its genetic material before dividing.
The heat is not merely tolerated for a few moments. Incendiamoeba grows between 42 and 63 °C, with optimal growth around 55 to 57 °C. At 64 °C, it no longer multiplies but remains capable of moving. Exposed to 70 °C, it can still recover when the temperature drops.
To understand this resistance, the team also studied its DNA and gene activity. Several mechanisms appear to contribute to its survival. The amoeba has more genes associated with protein maintenance and the stability of its genetic material. Under intense heat, it also increases the activity of genes involved in DNA repair.
It can also change shape when conditions become too hot. At high temperatures, it forms a protective envelope and enters a resting state. This ability allows it to temporarily endure conditions in which it can no longer feed or multiply. It resumes activity when its environment becomes favorable again.
In its hot spring, this resistance provides a very concrete advantage. The amoeba feeds on heat-adapted bacteria and occupies the top of this tiny food chain. At such temperatures, researchers found no microscopic animals capable of eating these amoebas. Competition for food is also reduced there.
The record remains far below that of certain forms of life without nuclei. The archaeon Methanopyrus kandleri can grow at temperatures up to 122 °C near deep hydrothermal vents. But eukaryotic cells have more internal structures that are sensitive to heat.
Researchers now want to understand which adaptations make this amoeba’s proteins so heat-resistant. Some could be of interest to biotechnology, particularly for designing enzymes that remain active at high temperatures. Similar genetic sequences have also been detected in other geothermal regions, opening the door to the discovery of new related species.