Surviving the Extremes: Exploring the Existence of Life at 125°

Lassen Volcanic National Park in California

Oliverio and Rappaport conducted field research over the summer at Lassen Volcanic National Park in California, which contains many hydrothermal features. Credit: Syracuse University

Biologists from Syracuse University are examining the processes that enable microbial eukaryotes to flourish in the harsh environment of a geothermal lake.

It is estimated that the Earth is home to around 8.7 million species of eukaryotic organisms. Eukaryotes are characterized by the presence of a nucleus and other membrane-bound organelles within their cells. Despite the common association of eukaryotes with animals and plants, these forms actually make up just two of the over six major eukaryotic groups.

A significant portion of eukaryotic diversity is made up of single-celled microorganisms known as protists. Researching these organisms allows scientists to explore the evolutionary paths that have contributed to the rich diversity and complexity of eukaryotic life. Such investigations provide understanding of the developments, such as the emergence of multicellularity, which enabled the existence of animal life on Earth.

As researchers work toward a better understanding of the mechanisms behind the evolution of species on Earth, questions remain about how microbial eukaryotes adapted to the planet’s extreme environments. To dive further into this topic, scientists in the College of Arts and Sciences’ (A&S’) Department of Biology are currently investigating protists that inhabit some of the harshest environments on Earth: extremely hot and acidic geothermal lakes.

Angela Oliverio and Hannah Rappaport

A&S biologists Angela Oliverio, left, and Hannah Rappaport at the United States’ largest geothermal lake at Lassen Volcanic National Park in California. Credit: Syracuse University

A team led by Angela Oliverio, assistant professor of biology, recently returned from Lassen Volcanic National Park in California, home to the largest geothermal lake in the U.S.

“This lake is an acid-sulfate steam-heated geothermal feature, meaning it is both quite hot (~52°C/124°F) and acidic (pH ~2),” says Oliverio, who started at Syracuse University in 2022. “This makes it a very unique environment to study polyextremophiles, which are organisms that have adapted to two or more extreme conditions – in this case, high temperature and low pH.”

So how did they know to travel to a hot lake in California to find microbial eukaryotic life? In a recent study published in Nature Communications co-authored by Oliverio and Hannah Rappaport, a researcher in Oliverio’s lab, the team built a database of previous studies that searched for microbial eukaryotic life across extreme environments. Specifically, they analyzed which eukaryotic lineages were detected multiple times from different studies under similar environmental conditions.

Amoebae and Red Algae

Image of amoebae (circular gray spots in the background) and red algae (four white ovals in the foreground), photographed by Hannah Rappaport using light microscopy. These were sampled from a geothermal lake at Lassen Volcanic National Park. Credit: Syracuse University

“We discovered that several lineages of amoebae were often recovered from extremely high-temperature environments,” says Oliverio. “This suggests that studying those lineages may yield great insight into how eukaryotic cells can adapt to life in extremely hot environments.”

According to Oliverio, one particular study conducted by Gordon Wolfe’s lab at Cal State Chico revealed an amoeba, T. thermoacidophilus, was quite abundant in Lassen National Park’s geothermal lake. However, no genomic data on this organism exists. Determining how this species adapted to this extreme environment could expand the understanding of what types of environments in the Universe may be considered suitable for life.

This past summer, Oliverio and Rappaport traveled to Lassen National Park to find out more about this particular protist and to search for other novel extremophilic eukaryotes. At the lake, the team used a long painter’s pole affixed with a 1-liter bottle to obtain samples – no easy task considering the water is well over 100 degrees Fahrenheit. Afterward, the bottles were transported back to Oliverio’s lab at Syracuse and the team is currently isolating single cells for genome sequencing and characterizing the amoebae by microscopy.

Researchers Obtain Sample From Geothermal Lake

Syracuse University researcher Hannah Rappaport dipping a bottle into a hot lake to obtain a sample. Due to the high temperature of the water and unstable ground, researchers must remain at a safe distance away when collecting samples. Credit: Syracuse University

While many unknowns remain about how eukaryotes adapt to exist in extreme environments, Oliverio is hopeful that this research will help close some of the current knowledge gaps.

Image of amoebae (circular gray spots in the background) and red algae (four white ovals in the foreground), photographed by Hannah Rappaport using light microscopy. These were sampled from a geothermal lake at Lassen Volcanic National Park.

“We suspect that there is something special about the amoeboid form that enables persistence in these eukaryotic lineages, but the mechanism remains unknown,” she says. “Based on our research, we hypothesize that horizontal gene transfer (movement of genetic information between organisms) from bacteria and genome reduction (when a genome deletes genes it does not need), along with the expansion of particularly useful gene families, may be a few of the ways in which protists have acquired the toolkit to survive in extreme environments.”

Oliverio notes that the team’s genome-scale findings will contribute important missing data into reconstructions of the tree of life. “This will further our understanding of the distribution and evolution of life on Earth.”

Reference: “Extreme environments offer an unprecedented opportunity to understand microbial eukaryotic ecology, evolution, and genome biology” by Hannah B. Rappaport and Angela M. Oliverio, 16 August 2023, Nature Communications.
DOI: 10.1038/s41467-023-40657-4

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