No Complex Life Was Supposed to Breed at 145°F. This One Does.

Quick Take

• Scientists thought no complex organism with a nucleus could survive above a certain temperature, but this amoeba shattered that limit in ways nobody predicted. See the discovery →
• When the heat gets extreme enough, this amoeba does something to its own body that no other amoeba has ever been observed doing. Explore its heat defenses →
• The fire amoeba's survival tricks could quietly fix a problem that makes life-saving medications inaccessible to millions of people. See the medical potential →
• Its discovery forces a question scientists have been reluctant to take seriously: are there environments across the solar system we've wrongly written off as lifeless? Explore life beyond Earth →

Our world has been growing increasingly hot over the last few hundred years. But humans aren’t built to handle the heat. The human body cannot withstand an internal temperature above 43°C (or 109.4°F) before leading to organ failure and death. However, that’s not true for all creatures on the planet. Certain species of archaea, or single-celled microorganisms, can live above the boiling point of water. The deep-sea Pompeii worm, a type of polychaete worm, also lives in high temperatures in hydrothermal ocean vents. The worm rests its head in cooler water, but its tail is exposed to extremely high temperatures inside its tube. Creatures that can survive high temperatures are known as extremophiles. Somewhat recently, scientists added a new extremophile to the list: an amoeba named Incendiamoeba cascadensis.

Nicknamed the “fire amoeba,” Incendiamoeba cascadensis not only lives at extreme temperatures, but can also replicate at high temperatures. If you’re wondering why that’s a big deal, it’s because high temperatures typically damage key parts of the cell, including the nucleus. The nucleus not only contains genetic material but also affects how cells function. So how is this amoeba surviving and thriving? Here’s what scientists know so far.

Discovering Incendiamoeba cascadensis

Researchers didn’t know what they were looking for when they began their study at California’s Lassen Volcanic National Park. The team, which included Dr. Angela Oliverio and PhD candidate Beryl Rappaport, collected and tested water samples from Hot Springs Creek to see what they might find. Rappaport, who examined the water in the lab, was shocked by the results. Under the microscope, she could see a small amoeba moving. Genomic testing showed it was an entirely new species. While examining the amoeba, the research team also learned that Incendiamoeba cascadensis feeds on filamentous bacteria.

The team isolated the amoeba and began conducting further tests. In the past, eukaryotes like Incendiamoeba cascadensis weren’t known to replicate over 60°C (140°F). Eukaryotes are organisms that have a nucleus and organelles (including humans!).

Incendiamoeba cascadensis differs from other eukaryotes because of its ability to withstand these temperatures. The researchers found that the amoeba could replicate at 63°C (145°F), move around up to 64°C (147°F), and even protect itself from harm in waters as hot as 70°C (158°F). Over a series of temperature tests, they also defined the amoeba as a thermophile, which means it thrives at high temperatures. Its optimal growth temperatures are 55°C (131°F) to 57°C (134.6°F), and the amoeba won’t replicate at under 40°C (104°F).

Heat Protection

According to research published in Cell, Incendiamoeba cascadensis has a unique way of protecting itself from extreme heat. When the water around them reaches 66°C (150.8°F), researchers believe the amoeba likely becomes rounder, forming a cyst, or a protective, dormant form of itself. By 70°C (158°F), the amoeba has completely formed a cyst.

But Incendiamoeba cascadensis also seems to be aware of, or at least taking into account, its environment. As the environment around the amoebas becomes hotter, the researchers write, “Encysting cells display rapidly moving, hair-like structures.” This is something that they believe is unique to these amoebas and is not seen in other amoebas.

The research team also discovered that these organisms have more genes associated with keeping proteins healthy and reducing cellular stress, more systems that can repair DNA and proteins damaged by heat and specialized positively charged proteins on the cellular surface. More research is needed to understand the exact function of these proteins. But one hypothesis is that the positive charge creates a protective layer between the amoeba and the heat.

What Could We Learn from This Amoeba?

If you look at a few decades ago in comparison to now, the scientific advancement we’ve made is clear. Humans have created increasingly complex technologies that have even gone as far as allowing us to modify our genomes. So, it might be strange to think that we could learn something from an organism that is functionally invisible to the human eye. And yet, there’s a lot that Incendiamoeba cascadensis could teach us.

Understanding more about this amoeba’s heat resistance could have far-reaching implications. As someone who works with the rare disease community, I’m aware that many orphan drugs, or medicines used to treat rare conditions, are chemically unstable. Many people I know must keep their medications refrigerated. Heat can degrade therapies or render them completely useless. The same goes for several medications that also treat more common illnesses. By studying how Incendiamoeba cascadensis protects itself, scientists could potentially develop therapeutics that are more stable and easier to transport and store. Similarly, the amoeba’s cellular repair mechanisms could give more insight into how we can mitigate cellular stress.

Beyond what we could potentially investigate within the human body, investigating Incendiamoeba cascadensis scientifically could also help with agricultural problems. Our world’s rising temperatures have already had an impact on crop yields. Warmer weather can prevent adequate reproduction in crops like corn and soybeans. With warmer weather also comes the spread of fungal diseases or pests that can destroy crops. Researchers are already estimating that our global food supply will decrease significantly. If scientists could figure out how to genetically modify crops to have cellular protections similar to the fire amoeba, plants could withstand stress and heat, providing us with more food.

Is Life Elsewhere Possible?

While all of this remains speculative for now, it’s exciting to think of what possibilities could emerge from this discovery. It opens up questions about the biodiversity of our world and of the solar system at large. What unexplored places have vibrant life that we haven’t considered, simply because we didn’t see them as livable? What creatures can survive in temperatures hotter or colder than we once thought? Is it possible for humans to engineer ways that we could survive in more challenging environments or on other planets? We may not know the answers yet, but it’s fascinating to think about.