Life at Extreme Heat: A New Record for Eukaryotes
We discovered an organism that lives at blistering temperatures – but what allows it to take the heat?
theconversation.com
Organisms are shaped by the environments where they live and evolve. The physical world follows universal laws, such as thermodynamics and gravity. Biology, however, has few rules that apply everywhere. One open question is how environmental conditions shape what organisms look like and how they live, breathe, and move.
Organisms can adapt to survive in many conditions. These range from salty water to extreme heat or cold and changing climates. Most eukaryotic organisms that have been studied live at temperatures close to those of the human body. Eukaryotes are organisms with cell types similar to our own. Their average temperature is about 95 degrees Fahrenheit (35 degrees Celsius).
Organisms that thrive above this range are called thermophiles. They could help answer a central question: what effect does temperature have on the rules for life? Those rules can help scientists understand where life might exist. In a study published in September 2026, our research team identified a new thermophile. It can survive at hotter conditions than any other previously recorded.
Discovering Life at a New Extreme
Eukaryotic cells, like the ones in our bodies, contain organelles such as nuclei and mitochondria. Eukaryotic organisms are reported less often than bacteria in extreme conditions. Based on observations of fungi at 140 F (60 C), scientists had theorized that eukaryotic life is not physically possible beyond 143 F (62 C).
In our new study, our team isolated and characterized a unicellular eukaryote, Incendiamoeba cascadensis. It can 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. We suspect it might also be found in other geothermal areas worldwide.
Like many amoebae, which are cells that change shape as they move, Incendiamoeba is a forager. It can move around in search of food and favorable conditions. It actively crawls at 147 F (64 C). But a few degrees more, and it will enter a protective, hibernation-like state.
What Sets Thermophiles Apart?
Bacteria have been recorded living up to 212 F (100 C). But it is unclear why eukaryotic cells are less amenable to high temperatures and other extremes. Many theories exist. Our cells have more protective membranes, including several membranes within each cell that surround their organelles. We also have complex molecular machinery that maintains our large genomes. In addition, we have 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 temperature.
As someone who investigates phenomena at the molecular level, I am always thinking about how molecules move and how motion increases with temperature. At higher temperatures, the velcrolike bonds holding proteins together can unfold. This prevents them from performing their vital functions. Eukaryotes have evolved protein helpers called heat shock proteins. These detect protein unfolding and help refold them.
So could Incendiamoeba simply have more of these helper proteins? Our team found that it does have a large reservoir of heat shock proteins. However, making these proteins requires a lot of energy, and they must be folded themselves. So more helper proteins probably is not the full answer.
Incendiamoeba also has a unique set of protein building blocks that are good at holding proteins together. Yet this composition may only make up for the fact that proteins degrade more easily as temperature increases.
We can look at Incendiamoeba’s genes, which turn on—or up—when temperature rises. Many of these genes are unknown. It is possible that one of these mystery genes is the key to its ability to withstand high temperatures. However, it is more likely, and in my mind much more interesting, that a symphony of small changes this organism has evolved confers its unique abilities.
By investigating Incendiamoeba and finding others like it, we can determine those changes. We can also learn about the key principles for how life works on our environmentally diverse planet.