For years the accepted upper limit for eukaryotic life, meaning any cell with a nucleus, sat at around 140 degrees Fahrenheit, or 60 Celsius, established by a few species of fungi and red algae. Researchers had gone further and proposed a mechanism: above roughly 62 Celsius the internal membranes surrounding a cell’s organelles should become unstable, which would make that a fundamental ceiling rather than merely an observed one.
In the geothermal tributaries of Hot Springs Creek in Lassen Volcanic National Park in Northern California, a NASA-supported team has found an amoeba that reproduces by division at 145 degrees Fahrenheit, 63 Celsius. They watched it undergo mitosis at that temperature. It keeps moving and hunting for food up to 147 Fahrenheit, 64 Celsius. In the lab it stays partially active at 150.8 and recovers from five minutes at 158. Only 176 proved too much.
It is called Incendiamoeba cascadensis, the fire amoeba of the Cascades, and the results were published in Cell. The team, including H. Beryl Rappaport and Angela Oliverio of Syracuse University, sampled twenty sites over three years in water around 65 Celsius.
The organism does not merely tolerate the heat. It requires it.
Angela Oliverio had named the gap in advance, and the framing is the most useful thing in the whole story. Geothermal springs are among the best studied ecosystems for bacteria and archaea, she noted, but we know extremely little about how eukaryotic cells withstand extreme conditions, which means our understanding of what eukaryotic cells can do is limited.
Nobody had looked properly. Extremophile research had concentrated almost entirely on simpler single-celled life, because that is where everyone expected to find things, and the ceiling for complex cells was inferred from the handful of species that happened to have been examined.
That is the shape of a great many limits in business, and it is worth naming plainly because it is so easy to inherit one without noticing.
Nobody will pay more than that for a coffee. Nobody comes to this street after seven. You cannot run a cafe profitably at under forty covers. A three-day lead time is the minimum in this trade. Every one of those is stated as a property of the world and is in fact a summary of what the people you happened to ask have observed. None of them were derived. They were collected, from a sample that was never designed to find the edge.
The test is whether anyone has actually gone and measured somewhere uncomfortable, or whether the number is the average of the places that were convenient to look.
The practical upshot for NASA is that the search for habitable worlds widens: if complex cells are more durable than assumed, more places in the universe become candidates for complex life.
Sixty-two Celsius was a reasonable prediction with a mechanism behind it.
Something was dividing at sixty-three the whole time.
Source: NASA Science, “NASA-Funded Research Finds Complex Life Defying Record Heat”
