Fire Amoeba Sets Temperature Record for Complex Cells

The organism, named Incendiamoeba cascadensis, which translates to 'fire amoeba of the Cascade mountain range,' was collected by Beryl Rappaport, a PhD student in the lab of Syracuse microbiologist Angela Oliverio. Rappaport used extra-long barbecue tongs to hold vials that she dipped into the hot water. Under a microscope, she saw an organism that protruded, retracted and fluidly changed shape, a characteristic form of amoeba movement, she recalled.

Laboratory work showed the amoeba can replicate at up to 145°F. It can continue moving at up to 147°F and protect itself in water as hot as 158°F, according to the researchers. Those temperatures exceed previous limits for eukaryotes, the group of organisms whose complex cells contain a nucleus and other structures. Bacteria and Archaea, which are simpler organisms, are known to live at or above 212°F, the boiling point of water, but heat tolerance has been less studied in eukaryotes.

Before the discovery, Rappaport said, scientists may simply not have found the right eukaryotes. 'So few have been described, especially in detail. We have a lot to learn from them,' she said.

Oliverio said the significance of the discovery lies less in the size of the temperature increase than in the proof that it is possible. She compared it to the sub-four-minute mile, a feat long thought impossible before one runner achieved it and others followed within weeks. 'It wasn't so much the incremental amount that this record was broken by, as much as the proof that it was possible,' she said.

The search took place in Lassen Volcanic National Park, which Oliverio described as one of the least-visited national parks in the United States. Rappaport called it mountainous and beautiful, with pines, butterflies and small steaming geothermal pockets. One sampling site was a tributary of Hot Springs Creek that was easy to miss because it was surrounded by tall grasses.

The team next investigated how the fire amoeba thrives at such high temperatures. Comparing its genome with those of other amoebas, the researchers found the new species has ways of keeping its proteins and membranes stable at higher temperatures, according to the study.

Oliverio said the finding could be used to expand the search for life. 'Thinking about not only what are the limits of life and what is possible here, but also what might be possible elsewhere,' she said. She also argued that the amoeba's temperature resilience could offer clues for creating heat-resilient crops or drugs that are stable across a wider range of temperatures.

Debashish Bhattacharya, an evolutionary biologist at Rutgers University who was not involved in the research, said it is difficult to turn an exotic extremophile into something with a major impact on other species. 'I can tell you from experience it's really hard to find a really cool exotic organism and actually turn it into something that has a major impact on other species,' he said. 'But there's always the potential of finding something amazing, that's for sure.' Bhattacharya added that other extremophiles have undergone genome streamlining, making their genomes more compact so they can compete with bacteria in harsh environments.