Scientists have identified a new fire amoeba species that can grow and divide at 145°F in volcanic hot springs in California, setting a record for complex life and forcing scientists to rethink how hot eukaryotic cells can get.
The organism, named Incendiamoeba cascadensis, is described in a late‑2025 preprint and has not yet been peer‑reviewed, but early results already have major implications for biology, climate science and the search for life beyond Earth.
What scientists found and where
The newly named species Incendiamoeba cascadensis—literally fire amoeba from the Cascades—was isolated from neutral‑pH geothermal streams in Lassen Volcanic National Park, in northern California’s Cascade Range. Researchers collected hot‑spring water from around 20 sites between 2023 and 2025 and detected the amoeba in 14 of those locations after culturing the samples in the lab.
In controlled experiments, the amoeba was observed actively growing and dividing at temperatures up to 63°C (145°F), which is higher than any previously known eukaryotic organism. Below about 42°C (107°F), the organism did not grow at all, confirming it as an obligate thermophile that requires high heat rather than merely tolerating it.
How the ‘fire amoeba’ survives such heat
In the lab, scientists placed the cultured amoebae into flasks held at 17 different temperatures from about 30°C to 64°C, feeding them indirectly via bacteria that grew on added grains, and recorded cell division rates at each step. The fastest growth occurred around 55–57°C (131–135°F), while direct observation of mitosis happened even at 58°C and 63°C, with cells still moving at 64°C.
When temperatures reached about 66°C (151°F), I. cascadensis began forming protective cysts—dormant, armoured stages that allow amoebae to ride out extreme stress—and the same encystment response appeared at an unusually warm low end of about 25°C (77°F). Genomic analyses suggest the species carries an expanded toolkit of heat‑shock proteins, chaperones and genes linked to protein stability and DNA protection, giving it an internal heat‑management system rare among complex cells.
Why this pushes life’s known limits
Before this discovery, the record for heat‑tolerant amoebae was about 57°C, held by Echinamoeba thermarum, and many biologists considered roughly 60°C the practical upper limit for sustained eukaryotic growth. Classic thermophilic pathogens such as Naegleria fowleri—the brain‑eating amoeba—grow best around 35–46°C, far below the temperatures that I. cascadensis treats as its comfort zone.
By moving the known eukaryotic growth ceiling to at least 63°C (145°F), I. cascadensis narrows, but does not erase, the gap between complex cells and ultra‑tough prokaryotes such as the archaeon Methanopyrus kandleri, which can tolerate more than 120°C near deep‑sea vents. Astrobiologists and extremophile researchers say the finding broadens the range of temperatures at which complex life might be viable on other worlds, especially around hydrothermal systems on Mars or icy moons.
Safety, climate context and what comes next
Scientists stress that Incendiamoeba cascadensis is currently known only as a free‑living environmental protist feeding on bacteria in isolated hot springs, with no evidence it infects humans or animals, unlike disease‑causing amoebae such as Acanthamoeba or Naegleria fowleri. However, the discovery is already being framed within a broader discussion about how warming surface waters and expanding hot, stagnant habitats may change the distribution of thermophilic microbes, including harmful species.
The team behind the discovery has posted its work as a preprint and is now refining genome analyses to understand the molecular adaptations that keep membranes, proteins and DNA intact at such high temperatures. Future research will likely focus on searching similar geothermal systems worldwide for related organisms, testing whether the 63°C record can be pushed even higher, and exploring potential applications for heat‑stable enzymes in biotechnology and industry.
Key temperature data and comparisons
The experiment shows a detailed temperature profile for I. cascadensis, from no growth at typical ambient conditions to dormancy and death at extreme heat. The table below summarises the most newsworthy points for readers and gives context against other well‑known organisms.
Temperature milestones for Incendiamoeba cascadensis
| Temperature | Observation |
| ~25°C (77°F) | Forms protective cysts rather than actively growing, unusually high low end for a eukaryote. |
| <42°C (<107°F) | No growth observed; water is effectively too cool for the amoeba to become active. |
| 55–57°C (131–135°F) | Fastest growth; optimal temperature range for cell division in lab cultures. |
| 58°C (136°F) | Mitosis directly observed under the microscope. |
| 63°C (145°F) | Amoeba still dividing, setting a new upper temperature record for eukaryotic growth. |
| 64°C (147°F) | Cells remain motile, although near their functional limit. |
| ~66°C (151°F) | Amoeba switches into cysts, entering a heat‑resistant dormant state. |
| 70°C (158°F) | Movement ceases; cells can revive if cooled. |
| 80°C (176°F) | Organism dies and cannot recover after cooling. |
Upper temperature limits for selected organisms
| Organism / group | Type | Approximate upper growth limit | Notes |
| Incendiamoeba cascadensis | Eukaryotic amoeba | 63°C (145°F) growth; motile slightly above this | New record for any known eukaryotic cell. |
| Echinamoeba thermarum | Eukaryotic amoeba | ~57°C (135°F) | Previous heat record among amoebae. |
| Red algae & some fungi | Eukaryotes | ~55–60°C (131–140°F) | Former benchmark for complex life in hot environments. |
| Naegleria fowleri | Pathogenic amoeba | Up to ~46°C (115°F) | Brain‑eating amoeba; thrives in very warm freshwater but far cooler than Lassen springs. |
| Typical Acanthamoeba spp. | Opportunistic pathogen | Up to ~42–45°C (107–113°F) | Causes eye and brain infections but not truly extreme‑heat specialists. |
| Methanopyrus kandleri | Archaeon (prokaryote) | >120°C (248°F) | Current overall temperature record‑holder, living on deep‑sea hydrothermal vents. |
The discovery of Incendiamoeba cascadensis thriving and dividing at 145°F redraws the thermal boundary for complex life, challenging long‑held assumptions about how hot a eukaryotic cell can function. By proving that an amoeba can not only survive but actively grow in conditions once thought impossible for such organisms, the research opens new questions about where similar extremophiles might exist on Earth and on other worlds with geothermal activity.
As scientists move from preprint to peer‑reviewed studies, they will probe the amoeba’s genome and proteins to understand its heat‑hardening tricks, with potential applications ranging from industrial enzymes to more robust biomedical tools. For now, the fire amoeba stands as both a record‑breaker and a reminder that life’s limits are still being mapped, one unexpected habitat at a time.
