Introducing Incendiamoeba cascadensis, which translates to “Cascade Range fire amoeba.” This single-celled organism can replicate at temperatures up to 145°F, a new record for a complex organism. Felix Mikus hide caption toggle caption Felix Mikus Angela Oliverio, a microbiologist at Syracuse University, studies the limit of what is possible. “There is a very deep curiosity and desire to understand life at its limits and in its most extreme aspects,” he says. “And where is that limit and what our limitations really are.” It’s no different than ultra-elite athletes who push themselves “to the maximum of what we believe is humanly possible,” he says. “But in this case, we’re just extending it to life in general,” specifically microscopic life. Oliverio studies organisms called Extremophiles, so called because they thrive in unusually harsh conditions, such as high temperatures. The headlines in this regard are simple organisms such as bacteria and a group called Archaea, with certain species living at 212°F or higher, the boiling point of water. But Beryl Rappaport, a doctoral student in Oliverio’s lab, says that until now, that same ability to combat heat has been less studied in eukaryotes, a group whose members include many different species, from humans to single-celled amoebas. These organisms have more complex cells that contain a nucleus and other structures. Rappaport says part of the reason may simply be that scientists haven’t found the right eukaryotes yet. “Very few have been described, especially in detail. We have a lot to learn from them.” Now, she and her colleagues have added a notable new organism to the pantheon: a species they call fire amoeba that raises a key temperature limit for complex cells by about five degrees higher. The findings were published in the journal Cell. This may seem like a modest improvement, but Oliverio believes that the sub-4-minute mile for runners was long thought to be impossible. However, once an athlete achieved it, it was only a few weeks before it happened again. “It wasn’t so much the incremental amount by which this record was broken, but rather the proof that it was possible,” he says. A small cell that likes heat To make this discovery, the researchers and their colleagues went on a fishing expedition of sorts in Lassen Volcanic National Park in Northern California. “It’s one of the least visited national parks in the United States,” Oliverio says. “It’s super nice,” Rappaport adds. “Very mountainous. All pine trees. Lots of butterflies fluttering around. It experienced some pretty intense fires in the last decade, so it grew a lot of new understory. And then just these little smoky geothermal pockets.” One of those areas is a tributary of a small waterway called Hot Springs Creek, “which you would almost miss because it’s surrounded by a lot of tall grasses,” Rappaport says. The research team decided to take some samples there by using extra-long barbecue tongs to grab a series of vials that Rappaport immersed in steaming water. Beryl Rappaport takes a sample from a tributary of Hot Springs Creek in Lassen Volcanic National Park in northern California. Kristen Skruber hide caption toggle caption Kristen Skruber Later, in the lab, she put the water samples under a microscope, filmed them, and sped up the footage. And that’s when he saw something move. It seemed to protrude, retract, and change shape fluidly, as if it were performing a single-cell version of hot yoga. “It’s definitely an amoeba,” he remembers thinking. “That’s the characteristic movement of amoebas.” This amoeba, however, was able to replicate at temperatures up to 145°F. This is a new record for a complex organism. It can also continue to move up to 147°F and protect itself in waters up to 158°F. When Rappaport and his colleagues studied its genome, they realized they had a new species on their hands. The team named it Incendiamoeba cascadensis, which translates to “Cascade Range fire amoeba.” An Extremophile with Lessons to Share The next question the researchers investigated was how the fire amoeba can thrive at such high temperatures. When they compared the genome of the new species with that of other amoebas, they observed that the fire amoeba had ways of keeping its proteins and membranes stable at higher temperatures. It is a finding that could be used to broaden the search for life. “Thinking not only about what the limits of life are and what is possible here, but also what might be possible in other places,” Oliverio says. Additionally, he argues that the amoeba’s temperature resistance could offer clues to help create heat-resistant crops or drugs that are stable over a wider range of temperatures. “I can say from experience that it’s really difficult to find a really interesting exotic organism and turn it into something that has a major impact on other species,” says Debashish Bhattacharya, an evolutionary biologist at Rutgers University who was not involved in the research. “But there’s always the chance to find something surprising, that’s for sure,” he adds. Bhattacharya says that in other Extremophiles, their genomes have become more compact. “It’s called genome streamlining,” he says, “so that they can then compete with bacteria that have smaller genomes and live in these hostile environments.” This is not the case with the fire amoeba, which has a larger genome than its relatives. “It’s taken a different path,” Bhattacharya says, “so I think it’s really interesting.” Oliverio finds it equally interesting. And now that the fire amoeba has been documented, he believes it’s just the beginning. He hopes more scientists will now look for other complex organisms with these extreme capabilities. “Maybe soon the temperature record will be broken again,” he says.
