Life in extreme heat: A California amoeba that thrives at record 63 degrees

Kristen Skruber

Organisms are products of the environments in which they live and evolve. While the physical world is governed by universal laws like thermodynamics and gravity, there are few laws of biology. An open question for biologists like me is how environmental conditions shape what organisms look like and dictate how they live, breathe and move.

Organisms can adapt to survive in a wide variety of conditions, including salty water, extreme heat or cold, and changing climates. Most eukaryotic organisms that have been studied with cell types similar to our own live at temperatures close to those of the human body, with an average of 35 degrees Celsius (95 degrees Fahrenheit).

Organisms thriving at temperatures higher than this range, known as thermophiles, could help directly answer what effect temperature has on the rules for life. These rules can help scientists learn more about where life could exist. In a study published in September 2026, our research team identified a new thermophile that can survive at hotter conditions than any other previously recorded.

Eukaryotic cells, like the ones found in our bodies, contain organelles like nuclei and mitochondria. Eukaryotic organisms are reported less often than bacteria in extreme conditions, and based on observations from fungi at 140 F (60 C), scientists had theorised that eukaryotic life is not physically possible beyond 143 F (62 C).

In our new study, our team isolated and characterised a unicellular eukaryote, Incendiamoeba cascadensis, which is able to reproduce at 145 F (63 C). This finding marks the highest temperature yet recorded for eukaryotic life.

Our team found Incendiamoeba cascadensis in geothermal springs in Lassen Volcanic National Park, in Northern California, but we suspect it might also be found in other geothermal areas worldwide.

Like many amoebae – cells that change shape as they move – Incendiamoeba is a forager. It can move around in search of food and favourable conditions. It actively crawls at 147 F (64 C), but a few degrees more and it will enter a protective hibernation-like state.

While bacteria have been recorded living up to 212 F (100 C), it is unclear why eukaryotic cells are less amenable to high temperatures and other extremes. Many theories abound: Our cells have more protective membranes, including several membranes within each cell, surrounding their organelles. We also have complex molecular machinery that maintains our large genomes, and a dynamic cytoskeleton: a network of proteins that allows our cells to move.

Like other eukaryotes, Incendiamoeba has organelles, an active cytoskeleton and a relatively large genome. So what allows it to persist where others cannot? So far, Incendiamoeba has revealed that we do not yet know which parts of eukaryotes are generally incompatible with high temperatures.

At higher temperatures, the velcro-like bonds holding proteins together can unfold, preventing them from performing their vital functions. Eukaryotes have evolved protein helpers called heat shock proteins, which detect protein unfolding and help refold them.

Skruber is Assistant Professor of Biology, Gonzaga University