Researchers descended into an underwater tunnel to study deep microbes

An international team of researchers studied the microbiome living at different depths in caves under

Scandinavian Peninsula and the Baltic Sea. The study showed that only microorganisms that can digest difficultly decomposable organic substances survive in the bowels of the Earth.

"Deep biosphere", or lithobiosphereis a microorganism that survives in the pores of rocks. According to scientists, it contains up to a quarter of all microbial biomass and plays an important role in the carbon cycle. But until now, scientists have not been able to understand how these microorganisms survive in the harsh and limited conditions of rocks.

To answer this question, researchersdescended into the underground laboratory of the Swedish Leibniz Institute for Baltic Sea Research. Under the center there is access to an underground system of tunnels about 3.6 km long, some of which run under the bottom of the Baltic Sea, and the other leads to the underground waters of the Scandinavian Shield.

Underground tunnel system. Image: Helena Osterholz et al., Nature Communications

The researchers took water samples withmicrobiome from different sources: some of them were fed by the waters of the Mediterranean Sea, the second - from the glaciers of Scandinavia, and the third - by the waters left over from the ancient sea. All water sources on the surface differ significantly in composition, properties and organic organisms that live in them. But, to the surprise of scientists, it turned out that the composition of the microbiota in all cases is approximately the same.

By studying the composition of dissolved organic substances inwater, the researchers came to the conclusion that simple organic substances, which are easy to decompose, serve as a source of nutrition for microorganisms located in the upper layers of the lithobiosphere, and only complex molecules descend to the very bottom, the decomposition of which takes a long time. As a result, only rare species of microorganisms that can feed only on these substances can survive in the underworld.

On the cover: underground laboratory tunnel. Photo: Margarita Lopez-Fernandez, IOW

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