Scientists Decode Genomes to Infer Lifestyles of Subsurface Microbes

An international team led by microbiologists Brett Baker of The University of Texas at Austin and Thijs Ettema of Uppsala University in Sweden have discovered genetic evidence that a group of subsurface microbes consumes carbon monoxide, a weak greenhouse gas, to produce energy. These microbes, first discovered in a gold mine two miles below South Africa, live in environments devoid of oxygen and light. So far, no one has successfully grown them in the laboratory, so it wasn't clear how these microbes generate energy.

Yellowstone hot spring. Photo credit: Dan Colman/Montana State University.

Baker, an assistant professor of marine science, and his colleagues found these microbes in vastly different environments of land and sea: the mud of a temperate estuary in North Carolina and underneath hot springs at Yellowstone National Park.

"This new class of microbes are specialized for survival beneath the surface, so we called them Hadesarchaea," says Baker, referring to Hades, the ancient Greek god of the underworld.

As its name suggests, the Hadesarchaea belong to a poorly studied group of microorganisms, the archaea. Like bacteria, archaea are single-celled and microscopically small, but from an evolutionary perspective, bacteria and archaea differ more from each other than a human does from a tree. The discovery of the Hadesarchaea will help increase our understanding of the biology and lifestyle of archaea that thrive in the deep biosphere.

In order to understand these elusive organisms, Baker and Ettema sequenced several of their genomes. By comparing their genomes to those of bacteria and other archaea, they found that Hadesarchaea share a set of genes that are known to be involved in the metabolism of carbon monoxide and hydrogen in other microbes. The finding suggests that Hadesarchaea are able to live in areas devoid of light and oxygen by using carbon monoxide as an energy source.

Carbon monoxide in the atmosphere is considered a weak greenhouse gas. It both contributes directly (albeit weakly) to the warming of our planet by blocking the escape of heat and indirectly by breaking down other chemicals that themselves break down much stronger greenhouse gases like methane.

"It's not clear yet what role Hadesarchaea have in the global carbon cycle or our climate," says Baker. "But because they are found in the subsurface all over the world, they are likely very important players."