Summary
NASA-funded research reports that Incendiamoeba cascadensis can reproduce at 63°C in heated waters at California’s Lassen Volcanic National Park. The finding raises the known upper temperature limit for reproduction among eukaryotes.
NASA-funded research reports that the amoeba Incendiamoeba cascadensis can reproduce at 63°C in heated waters at California’s Lassen Volcanic National Park. The result sets the highest known temperature at which a eukaryote reproduces, according to NASA; the findings were published in Cell.
The distinction between reproduction and survival matters. NASA says the amoeba stops reproducing above 63°C but can still move while searching for food at up to 64°C. In laboratory tests described with the research, it remained partly active at 66°C and recovered after five minutes at 70°C. Exposure to 80°C was too much for it to recover from. Those higher-temperature responses do not mean it can reproduce at those temperatures.
Why the temperature is notable
Eukaryotes are organisms whose cells have a nucleus and membrane-bound structures, including mitochondria. The group includes animals and plants, but also single-celled organisms such as this amoeba. Heat can damage proteins and other molecules, while disrupting cell membranes. Researchers had proposed that membranes in eukaryotic organelles might not remain stable above 62°C.
Before this finding, the reported upper limit for eukaryote reproduction was 60°C, reached by a few fungi and red algae. The new observation extends that known limit by 3°C. By comparison, many earlier studies of life in extreme heat have focused on bacteria and archaea, whose cells lack a nucleus and membrane-bound organelles.
The research team sequenced the amoeba’s genome and examined gene expression at multiple temperatures. NASA reports that the analysis identified genes associated with stabilising DNA and maintaining protein folding, with some gene activity increasing at high temperatures. The researchers also identified proteins with a strongly positive surface charge, a feature they say resembles proteins in heat-tolerant bacteria and archaea. These findings offer possible clues to the amoeba’s heat tolerance, rather than a complete account of how it works.
What the discovery means for astrobiology
Extremophiles help researchers investigate the environmental limits of life as it is known on Earth. Finding a eukaryote reproducing at this temperature expands the range of conditions in which complex cells are known to function, a useful constraint when considering where life might persist elsewhere.
The team also found DNA sequences resembling parts of the amoeba’s genetic information in geothermal samples from locations including New Zealand and Yellowstone National Park. NASA presents this as a reason to look for related heat-tolerant amoebas in other geothermal environments; the matching sequences are not, by themselves, confirmation that the organism lives at those sites.
The result does not make temperature the only requirement for life beyond Earth. The study’s lead author notes that I. cascadensis depends on conditions including suitable acidity, oxygen, pressure, water and food, as well as support from other life. The finding informs the search for possible habitats, but it does not establish that this amoeba—or another complex organism—could live on another planet.