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Mechanism on the ocean floor.
Collecting water samples from the subseafloor. Credit: WHOI, UCSC, US NSF.

A study has revealed how a group of deep-sea microbes provides clues to the evolution of life on Earth, in a recent paper in The ISME Journal.

Researchers from the University of Hawaiʻi at Mānoa and others used cutting-edge molecular methods to study these microbes, which thrive in the hot, oxygen-free fluids that flow through Earth’s crust. Called Hydrothermarchaeota, this group of microbes lives in such an extreme environment that they have never been cultivated in a laboratory for study.

Stephanie Carr, at right, works with a student to process deep-sea samples aboard the Atlantis research vessel. Credit: Beth Orcutt, Bigelow Laboratory for Ocean Sciences.

A research team from the Hawaiʻi Institute of Marine Biology (HIMB) in the School of Ocean and Earth Science and Technology (SOEST), Bigelow Laboratory for Ocean Sciences in Maine and the U.S. Department of Energy Joint Genome Institute bypassed the problem of cultivation with novel genetic sequencing methods to detect and sequence individual cells or entire natural microbial communities.

Genetic evidence reveals unexpected survival strategies

The researchers found that Hydrothermarchaeota might obtain energy by processing carbon monoxide and sulfate, which is an unexpected and previously overlooked metabolic strategy within Earth’s crust.

“Discovering this metabolic strategy in a group of microbes that is abundant in the crustal fluids of the Juan de Fuca Ridge flank provides clues about how life may be sustained deep within Earth’s crust, and also yields clues regarding the types of metabolic strategies that may occur on or within other planets,” said Michael Rappé, research professor at HIMB and one of the study’s senior authors.

The Juan de Fuca Ridge is an underwater volcanic range that stretches for about 300 miles along the Pacific Northwest coast.

Analyzing Hydrothermarchaeota genomes revealed that these microbes belong to the group of single-celled life known as archaea and evolved early in the history of life on Earth—as did their unusual metabolic processes. These observations suggest that the subsurface ocean crust is an important habitat for understanding how life evolved on Earth, and potentially other planets.

The researchers also found genetic evidence that Hydrothermarchaeota have the ability to move on their own. Motility offers a valuable survival strategy for the extreme environment they call home, which has a limited supply of nutrients essential to life.

For the full story, see the SOEST website.

—By Marcie Grabowski

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