Photo of rocky hot springs covered by yellow microbial mats
Behold Ethiopia’s Dallol hot springs: salty, highly acidic, and nearly boiling. Credit: Achilli Family | Journeys, CC BY 2.0

There’s nothing relaxing about soaking in Ethiopia’s Dallol hot springs—they’re as acidic as battery acid and nearly boiling. But fieldwork in this extreme world suggests that the hot springs are home to tiny, spherical organisms whose relatives might have once thrived on Mars, new research shows.

“It’s a really interesting, extreme environment.” It also looks “like hell.”

Felipe Gómez, an astrobiologist at the Astrobiology Center—National Institute of Aerospace Technology in Madrid, and his colleagues traveled to the Danakil Depression in northern Ethiopia in January 2017. They were there, in one of the lowest spots on Earth, to study an otherworldly landscape: a salt plain near the Dallol volcano.

Magma just below the surface heats the groundwater, dissolving salts and producing bright yellow, orange, and red mineral formations known as “chimneys” that spew briny, nearly boiling water. A sulfurous, yellow-tinged fog occasionally envelops the area, forcing anyone nearby to evacuate.

“It’s a really interesting, extreme environment,” said Gómez. It also looks “like hell.”

A Surprise in the Salt

The researchers focused on a chimney roughly 1 meter tall and scraped salt precipitates from its walls into sterile glass vials. Back in the lab, they extracted DNA from the samples and found a close match with the class Nanohaloarchaea, tiny, salt-loving organisms similar to those spotted in hypersaline ponds in Spain.

Using imaging techniques such as scanning electron microscopy and transmission electron microscopy, Gómez and his team recorded spherical structures approximately 50–500 nanometers in size. That’s smaller than most archaea, said Gómez. On the basis of the structures’ high carbon content, the researchers concluded they were biological.

Finding these microorganisms was a surprise, said Gómez, because Nanohaloarchaea haven’t been spotted in acidic, high-temperature environments before.

Implications for Early Mars

This discovery has implications for what forms of life might have thrived on Mars long ago, Gómez and his team propose.

“The presence of life in the Dallol hot springs expands our understanding of the limits of habitability on Earth and beyond.”

Early Mars was volcanically active, and some regions, such as Nili Patera Caldera, might have resembled the geology of the Dallol hot springs, the researchers stated in their paper, published in Scientific Reports in May. “The presence of life in the Dallol hot springs expands our understanding of the limits of habitability on Earth and beyond,” they wrote.

Although these results are promising, follow-on work is necessary, said Kenneth Stedman, a virologist at Portland State University in Oregon who was not involved in the research.

An important next step will be to show that these microorganisms are metabolically active, said Stedman, to rule out that they were blown into the salt and preserved there. It’s also critical to study samples taken directly from the brines, said Stedman. “I’d like to see what’s in the water.”

—Katherine Kornei (@katherinekornei), Freelance Science Journalist


Kornei, K. (2019), Microbes spotted in “polyextreme” hot springs, Eos, 100, Published on 24 June 2019.

Text © 2019. The authors. CC BY-NC-ND 3.0
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