The 145°F survival mystery: How a tiny California 'fire' amoeba thrives where complex life was thought impossible

For many years, excessive heat has been known as one of the most notable limitations to complex organisms. In today’s world, however, an organism discovered within the landscape of volcanoes in California seems to be setting new levels for this limitation.

NASA-funded research has been able to uncover the presence of an amoeba which can replicate at extremely high temperatures such as 145 degrees Fahrenheit (63 degrees Celsius).

It is noteworthy because it is currently considered the highest temperature at which eukaryotes can replicate themselves. The amoeba has been named the Fire Amoeba owing to its remarkable resistance to high temperatures.


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The Fire Amoeba was discovered in the geothermal waters of the Lassen Volcanic National Park.

Scientists watched this amoeba replicate and multiply under conditions previously thought impossible for complex organisms to tolerate.

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At 145 degrees Fahrenheit, the replication process ceases, but the level of its tolerance to high temperatures does not end there. It was revealed that even in water with a temperature higher than 147 degrees Fahrenheit (64 degrees Celsius) while looking for nutrients, the amoeba can be active.

These discoveries were revealed in the journal Cell.

A record hidden in volcanic water

I. cascadensis is one of the eukaryotes, meaning that the cells of this organism have a nucleus and many other complex organelles surrounded by membranes.

Heat impacts proteins, destroys membranes of cells, and leads to denaturation of other organic molecules. Additionally, eukaryotic cells contain very sensitive structures inside, which makes them look like organisms that are very sensitive to harsh environments.

Before the discovery of the fire amoeba, the highest temperature tolerance limit for eukaryotes was around 140°F (60°C) and was associated with fungi and some species of red algae.

Thus, the discovery of the new amoeba reveals not only its heat tolerance, but also the fact that this organism can perform reproduction at a higher temperature than any other eukaryote before.

According to scientists, it can be partially explained by how biologists try to discover life forms in extreme habitats. If it was assumed that eukaryotes cannot live in such conditions, then the presence of these organisms near the limit has been unnoticed.

According to Beryl Rappaport, a graduate student from Syracuse University and one of the authors of the study, some assumptions about membrane stability have limited searches for high-temperature eukaryotes before.

How the fire amoeba protects its cells

The natural question is then how the creature, with its complicated cellular machinery, can survive in such conditions that can harm the structure of proteins and membranes.

To find out more, the scientists sequenced the genome of I. cascadensis and analysed the behaviour of its genes under various temperatures.

Several approaches to survival became evident.

Some of them are connected with DNA protection and prevention of its breakdown in cases of heat stress. Some others allow the amoeba to respond to the changing environment around it. Increased activity was registered in genes responsible for keeping proteins in proper condition at higher temperatures.

Protein stability becomes especially significant since high temperatures may cause proteins to become unstructured.

Moreover, the scientists found proteins with very high surface charge. In the research, such features were noted earlier in thermophilic bacteria and archaea. Thus, some approaches to survival in extreme temperature environments might be common even between very different kinds of living creatures.

Finally, comparing the genome of the amoeba to data from other geothermal sources, the team found related DNA in areas ranging from Yellowstone National Park to New Zealand.

Why the discovery matters for life beyond Earth

The extremophile organisms are particularly interesting to astrobiologists since they help in understanding the limits of life through practical means.

Extreme organisms live in habitats where there are various stressful conditions, including high temperatures, acidity, radiation, and others. Through studying them, scientists can identify biological processes that function under stress conditions.

However, the fire amoeba shows that even complex organisms are capable of surviving at higher temperatures than what was known before.

It becomes important when scientists think about areas outside the Earth. For instance, Mars is much harsher than Earth, while other planets have subsurface environments and different chemicals on their surfaces from those on the surface of the Earth.

Alison Olcott, the program scientist for Exobiology at NASA Headquarters, says that research on extremophiles helps scientists know the biochemical and physiological limits of life as it functions on Earth. These limits will help in searching for life outside.

However, it does not mean that scientists have discovered any sign of extraterrestrial life.

Temperatures are just a part of the requirements. In addition to temperature, an organism should have water, acidity, oxygen conditions, pressure, nutrients, and other organisms in its ecosystem.

A new temperature boundary for complex life

The most striking part of the discovery may be what it says about scientific assumptions.

For years, extremely high temperatures were considered especially problematic for eukaryotes because of their complicated internal structures. Incendiamoeba cascadensis shows that at least one eukaryotic organism can reproduce at temperatures reaching 145°F.

It also demonstrates that survival and reproduction are not necessarily the same thing. The amoeba can remain active at temperatures slightly above its reproductive limit, moving through its environment and looking for food even after it can no longer divide.

That distinction gives researchers another way to study the limits of life.

Rappaport cautioned that I. cascadensis could not simply be placed on another planet and expected to survive. Its environment would need to provide the broader conditions required by its ecosystem.

Still, the discovery expands the known range of environments in which complex cellular life can function.

The fire amoeba was found in a place where heat, geology and biology intersect. Its existence suggests that the boundary scientists once placed around complex life was not quite as fixed as it appeared.

And somewhere in another hot spring, researchers may now be looking for the next organism that was previously assumed to be impossible.

FAQ

1. What is a fire amoeba?

Incendiamoeba cascadensis is a type of amoeba that was discovered relatively recently, dwelling in hot water of Lassen Volcanic National Park in California. This type of amoeba is defined by its capability to reproduce itself in temperatures up to 145°F (63°C).

2. In which temperature range is the fire amoeba capable of surviving?

The amoeba reproduces itself in temperatures up to 145°F (63°C). It was observed alive and moving in temperatures close to 147°F (64°C), but unable to reproduce anymore, as it is over the reproductive limit.

3. Why is this discovery important to scientists?

It is the hottest known eukaryote that reproduces itself. This finding breaks all previous beliefs about the heat tolerance of complex cells and helps scientists to learn more about the limits of life's existence.

4. Can this discovery help in the search for life on other planets?

Indirectly, yes. Extremophiles help scientists to figure out the environmental limits of life on Earth and can be useful in the search of habitable areas on other planets. But this discovery itself is not proof of life beyond Earth.