In the steaming springs of Lassen Volcanic National Park in Northern California, a newly named amoeba, Incendiamoeba cascadensis, has been found dividing in water near 63 degrees Celsius, a temperature that quietly crosses a boundary scientists had long believed complex cells could not pass. It is a reminder that the rules of life are still being written, and that the limits we assumed were often limits of our imagination rather than of nature. Researchers, led by a team including biologist Skruber of Gonzaga University, have described the find in a study published in September 2026. What it m
A California Amoeba Thrives at 63°C, Pushing the Known Upper Limit for Complex Life
It reproduces at 63 degrees, just past a proposed ceiling for complex life
Mark
So what is the actual headline here? A microbe in a hot spring?
Mimi
It's a eukaryote reproducing at 63 degrees Celsius. That's the highest recorded for cells like ours, with nuclei and mitochondria.
Mark
Why does one degree matter? The old theoretical limit was 62.
Luke
Careful. The 62 was a theory built on fungi observed at 60. It was never a measured wall. So one degree past a proposed ceiling is notable, but it isn't a dramatic break.
Mimi
Fair. What's striking is that the amoeba isn't simplified. It has organelles, a cytoskeleton and a large genome, the very features thought to make eukaryotes fragile in heat.
Mark
So what's protecting it?
Luke
That's not answered. The piece mentions heat shock proteins as a general eukaryote tool, but it doesn't say they explain this organism.
Mimi
Right, the author says we still don't know which eukaryote features are incompatible with high temperatures.
Mark
Is it only in Lassen?
Luke
It was found there. The idea that it lives in other geothermal areas is a suspicion, not a finding.
Mimi
And note it crawls at 64 and hibernates a few degrees above that, so 63 isn't necessarily its ceiling for survival.
Mark
And the link to life elsewhere?
Luke
That's a hope about what the rules might eventually teach us. Nothing here says anything about other planets.
Le Pouls
- A single-celled eukaryote has been found reproducing at 63 degrees Celsius, pushing past the long-assumed heat ceiling for complex cells.
- Scientists who believed eukaryotes were too fragile for such heat now face an organism built with the very features they thought made heat intolerance inevitable.
- The team isolated the amoeba from geothermal springs in Lassen Volcanic National Park and found it actively crawling at 64 degrees, with hibernation-like survival just above that.
- Researchers are now working to uncover how the amoeba keeps its protective membranes, molecular machinery and cytoskeleton functioning in extreme heat.
- The discovery is already reshaping the known temperature limits for complex life, with the likelihood of relatives in other hot springs widening the search.
In the steaming springs of Lassen Volcanic National Park in Northern California, a newly named amoeba, Incendiamoeba cascadensis, has been found dividing in water near 63 degrees Celsius, a temperature that quietly crosses a boundary scientists had long believed complex cells could not pass. It is a reminder that the rules of life are still being written, and that the limits we assumed were often limits of our imagination rather than of nature. Researchers, led by a team including biologist Skruber of Gonzaga University, have described the find in a study published in September 2026. What it means for the wider search for life, on Earth and beyond, remains an open and humbling question.
In the geothermal springs of Lassen Volcanic National Park in Northern California, a single-celled organism is dividing in water hot enough to burn skin. A research team has isolated it, named it Incendiamoeba cascadensis, and reported that it multiplies at 63 degrees Celsius, the highest temperature yet recorded for eukaryotic life, meaning organisms whose cells contain nuclei and organelles like our own.
Member Skruber, an assistant professor of biology at Gonzaga University, describes the work in a first-person account published in September 2026. The starting point, as the author frames it, is that biology has few fixed laws to match thermodynamics or gravity, and scientists are still learning how environment shapes the way organisms live, breathe and move. Most eukaryotes studied live near human body temperature, so thermophiles like this one offer a test of how heat bends the rules of life.
Eukaryotes rarely appear in extreme conditions, unlike bacteria, which have been recorded up to 100 degrees. Earlier observations of fungi had led scientists to suspect complex life was physically impossible beyond 62 degrees. This amoeba, a cell that changes shape as it forages, sits just past that proposed ceiling and keeps crawling at 64 degrees, with hibernation-like protection a few degrees higher.
What puzzles researchers is that the amoeba has all the features once thought to doom complex cells in heat: protective membranes, a large genome, and a dynamic cytoskeleton. The author suggests scientists do not yet know which parts of eukaryotes truly clash with high temperatures. How it preserves its proteins, which heat normally unravels, remains unexplained.
The next steps are to discover what keeps this amoeba's machinery working at 63 degrees and whether relatives thrive in other hot springs. The answers could redraw the known limits of complex life and widen where we look for it.
In the geothermal springs of Lassen Volcanic National Park in Northern California, a single-celled organism is reproducing in water hot enough to be dangerous to touch. A research team has isolated and characterised it, named it Incendiamoeba cascadensis, and reported that it can multiply at 63 degrees Celsius (145 Fahrenheit). That is the highest temperature yet recorded for eukaryotic life.
The account comes from a member of the team, Skruber, an assistant professor of biology at Gonzaga University, who describes the work in a first-person piece. The study was published in September 2026. The starting point, as the author puts it, is that there are few laws of biology to match the laws of thermodynamics or gravity, and biologists are still asking how environmental conditions shape what organisms look like and how they live, breathe and move.
Eukaryotes are organisms whose cells contain organelles such as nuclei and mitochondria, as human cells do. Most of the eukaryotes that have been studied live near human body temperature, with an average around 35 degrees Celsius (95 Fahrenheit). Organisms that thrive at higher temperatures, called thermophiles, offer a way to test what heat does to the rules of life, and those rules could help scientists judge where life might exist.
Eukaryotes turn up in extreme conditions less often than bacteria do. Bacteria have been recorded living at up to 100 degrees Celsius (212 Fahrenheit). Observations of fungi at 60 degrees Celsius (140 Fahrenheit) had led scientists to theorise that eukaryotic life was physically impossible beyond 62 degrees (143 Fahrenheit). Incendiamoeba cascadensis, reproducing at 63, now sits just past that proposed ceiling.
Like many amoebae, which are cells that change shape as they move, it is a forager, crawling in search of food and favourable conditions. It keeps actively crawling at 64 degrees Celsius (147 Fahrenheit). A few degrees hotter and it enters a protective, hibernation-like state. The team found it in the Lassen springs but suspects it may live in other geothermal areas around the world.
What makes the finding puzzling is that the amoeba is built like other eukaryotes. It has organelles, an active cytoskeleton (the network of proteins that lets cells move) and a relatively large genome. Several theories try to explain why eukaryotes tolerate heat poorly: their cells contain many protective membranes, including those around the organelles, and they rely on complex molecular machinery to maintain large genomes, along with that dynamic cytoskeleton. Yet this organism has all of those features and persists in the heat anyway. According to the author, it shows that scientists do not yet know which parts of eukaryotes are generally incompatible with high temperatures.
Heat attacks proteins directly. At higher temperatures the velcro-like bonds that hold proteins in shape can come apart, and unfolded proteins cannot do their jobs. Eukaryotes have evolved heat shock proteins, helpers that detect unfolding and help refold the damaged proteins. The source does not say how Incendiamoeba manages its heat tolerance, so that question remains open.
The next step is to learn what lets this amoeba keep its complex cell machinery working at 63 degrees, and whether relatives live in other hot springs. The answers could redraw the known temperature limit for complex life and widen the range of places where it might exist.
Citations marquantes
Incendiamoeba has revealed that we do not yet know which parts of eukaryotes are generally incompatible with high temperatures.— Skruber, assistant professor of biology, Gonzaga University (paraphrased)
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