NASA-supported scientists have discovered an amoeba that can reproduce at temperatures previously considered too extreme for complex life, setting a new upper-temperature record for known eukaryotes.
The organism, Incendiamoeba cascadensis, was found in the heated waters of California’s Lassen Volcanic National Park and can reproduce by division at 145 degrees Fahrenheit (63 degrees Celsius).
The amoeba, also known as the fire amoeba, stops reproducing above that temperature but remains active and can move in search of food at up to 147 degrees Fahrenheit (64 degrees Celsius).
The previous upper temperature limit for eukaryotes was 140 degrees Fahrenheit (60 degrees Celsius), based on several species of fungi and red algae.
High temperatures can destroy proteins, biomolecules and cell membranes needed for survival, while the complex cells of eukaryotes contain a nucleus and membrane-bound organelles that were thought to be particularly vulnerable to extreme heat.
“In part, studies on eukaryotes may have been limited because of assumptions about membrane stability,” says Beryl Rappaport, graduate student at Syracuse University and lead author of the study.
“We are hoping that the discovery of I. cascadensis encourages others to keep searching for high temperature eukaryotes.”
The researchers sequenced the amoeba’s genome and examined gene expression at multiple temperatures.
They identified genes that help stabilize DNA, protect proteins and sense environmental conditions, while some genes involved in maintaining protein folding became more active at high temperatures.
“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,” says Rappaport.
The researchers also found similar pieces of DNA in geothermal samples from New Zealand and Yellowstone National Park, suggesting that related heat-tolerant amoebas may exist elsewhere.
Meanwhile, the discovery could inform the search for life beyond Earth by expanding scientists’ understanding of the conditions under which complex organisms might survive.
“Studying extremophiles helps us better understand the biochemical and physiological limitations of life as we know it on Earth,” says Alison Olcott, program scientist for Exobiology at NASA Headquarters in Washington.
“This information, in turn, helps guide NASA’s search for life as it expands the range of conditions we think life could potentially be inhabiting elsewhere.”
Rappaport cautioned that temperature alone does not determine whether an organism can survive.
“It’s not just about temperature. An environment also needs the right acidity, oxygen levels, pressure, water, and food.”