Amoeba Incendiamoeba cascadensis divides at 63 °C, a new heat record for eukaryotes

NASA-supported scientists have described an amoeba from the heated waters of California's Lassen Volcanic National Park that reproduces by division at 145 °F (63 °C), according to science.nasa.gov. This is the highest temperature known for any eukaryote science.nasa.govscience.nasa.govscience.nasa.govOpen source ↗. The organism, Incendiamoeba cascadensis, also called the fire amoeba, was reported in the journal Cell science.nasa.govscience.nasa.govscience.nasa.govOpen source ↗.

The amoeba stops reproducing above 145 °F but stays active: it keeps moving and searching for food at up to 147 °F (64 °C) science.nasa.govscience.nasa.govscience.nasa.govOpen source ↗. The previous eukaryote limit, 140 °F (60 °C), was set by a few species of fungi and red algae science.nasa.govscience.nasa.govscience.nasa.govOpen source ↗.

Why heat is hard on complex cells

Eukaryotes have a nucleus that encases fragile genetic information, along with membrane-bound organelles such as mitochondria and the endoplasmic reticulum. High temperatures break down proteins and other biomolecules and can cause membranes to fall apart science.nasa.govscience.nasa.govscience.nasa.govOpen source ↗. It had been suggested that organelle membranes in eukaryotes could not remain stable above 144 °F (62 °C). The discovery of I. cascadensis shows this assumption to be wrong science.nasa.govscience.nasa.govscience.nasa.govOpen source ↗.

Previous extremophile research has focused mostly on single-celled bacteria and archaea, which have no nucleus or membrane-bound organelles and therefore less cellular machinery to damage science.nasa.govscience.nasa.govscience.nasa.govOpen source ↗. To count as a true thermophile, an organism must replicate, move, eat and survive above 113 °F (45 °C) science.nasa.govscience.nasa.govscience.nasa.govOpen source ↗.

Genome and protein adaptations

The team sequenced the I. cascadensis genome and studied gene expression at several temperatures. They found many genes that help stabilize DNA and protect it from breakdown, and others that let the organism sense its environment. At high temperatures the expression of certain genes rose, including those involved in maintaining protein folding science.nasa.govscience.nasa.govscience.nasa.govOpen source ↗.

Some proteins of the amoeba carry a high positive surface charge, which could help keep them stable. Similar charges are found in thermophilic bacteria and archaea, said lead author Beryl Rappaport of Syracuse University science.nasa.govscience.nasa.govscience.nasa.govOpen source ↗.

Comparing data from other studies, the authors found similar DNA fragments in geothermal samples from New Zealand and Yellowstone National Park. This suggests that related thermophilic amoebas may live elsewhere in the world science.nasa.govscience.nasa.govscience.nasa.govOpen source ↗. Alison Olcott, program scientist for Exobiology at NASA Headquarters, noted that such work helps guide NASA's search for life by widening the range of conditions in which life might exist science.nasa.govscience.nasa.govscience.nasa.govOpen source ↗.