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Tristan Free
This newly discovered amoeba can survive and thrive at temperatures once thought impossible for complex lifeforms.
The aptly named fire amoeba (Incendiamoeba cascadensis) can reproduce by division at a sweltering 63°C, a new upper temperature limit for eukaryotes. Even more shockingly, it can survive as temperatures creep above this, remaining active at up to 64°C. The novel extremophile, discovered by researchers at Syracuse University (NY, USA), expands our understanding of where and how life can persist on Earth, and maybe beyond.
Previous research into the thermal limits of life has largely focused on single-celled bacteria and archaea. The highest known temperature an organism can survive is 122°C, a record held by the archaeon Methanopyrus kandleri. In contrast, attempts to define upper temperature thresholds in more complex lifeforms have been lacking. Since their discovery, no eukaryote has been found to replicate at temperatures above 60°C. As a result, the bulk of eukaryotic diversity in extreme heat remains unexplored.
In a step toward remedying this, the researchers isolated a new genus of amoeba from geothermal springs in Lassen Volcanic National Park (CA, USA). To their surprise, ultrastructure expansion microscopy revealed that the hardy organism continued to divide at 63°C and, according to high-temperature live-cell microscopy and cell centroid tracking, it was motile up to 64°F – a new record for eukaryotes.
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Diving deeper into the fire amoeba’s genetics, the team assembled two genomes using long-read sequencing and identified a suite of genes related to DNA stabilization, proteostasis and environmental sensing, all of which were enriched compared to more mesophilic (preferring of moderate temperatures) amoebae. Moreover, comparative RNA sequencing of I. cascadensis grown at 48°C versus 61°C demonstrated that, at high temperatures, pathways related to proteome maintenance, DNA repair and membrane trafficking were upregulated. On the other hand, energy and biosynthesis pathways were downregulated in the higher-temperature condition.
The researchers then used AlphaFold2 to predict protein sequences from I. cascadensis, noting that they had distinct biophysical properties that could help them remain stable, such as an enrichment of positively charged surface residues, similar to thermophilic bacteria and archaea. This, the team suggests, points to a convergent mechanism for protein stability under temperature stress.
“We were able to uncover many strategies that could help I. cascadensis survive at high temperatures, and some of these strategies could be used by thermophiles across all life,” lead author Beryl Rappaport summarized.
The team also compared Incendiamoeba sequences with genetic information from previous studies, identifying similar sequences in the Taupō Volcanic Zone (New Zealand) and Yellowstone National Park (WY, USA), suggesting that related thermophilic amoebae could be found in geothermal areas across the globe.
“We are hoping that the discovery of I. cascadensis encourages others to keep searching for high temperature eukaryotes,” Rappaport continued.
Studying extremophiles on Earth could also have implications in the search for life on other worlds, expanding the range of habitats we could explore for extraterrestrial lifeforms.
The post Too hot to handle? ‘Fire amoeba’ beats the heat to survive at a record-breaking 63°C appeared first on BioTechniques.
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