'Deep biosphere' shaped by dissolved organic material from Earth's surface

TheInstitut fr Ostseeforschung Warnemnde is located in Berlin.

In the latest issue of the journal Nature Communications, a research team with lead authorHelena Osterholz of the Leibniz Institute for Baltic Sea Research report on possible pathways by which microbes can ensure survival. There was an investigation of dissolved organic matter. Most of the labile matter is converted in the uppermost layers. The process of mixing dominates below that. There is a core microbiome that can feed on this hard-to-digest food.

There is a deep biosphere that extends several kilometers down into the lithoosphere, where the cycle of life is driven mainly by photosynthesis. It is an important contributor to the Earth's carbon budget, as it contains 25% of the total global microbes. This biosphere comes into contact with a wide range of dissolved organic matter. It's possible that this DOM is a major food source. The role that the composition and associated bioavailability of these substances play in the nutrition of the deep continental biosphere is unknown.

This is due to the fact that it is very hard to get to this world. Excellent research conditions can be found at the sp Hard Rock laboratory. There is a 3.6 km tunnel system under the Baltic Sea that provides access to underground water.

A German-Swedish team with researchers from Linnaeus University, Kalmar, Swedish University of Agricultural Sciences, Uppsala, and the sp Hard Rock Laboratory obtained water samples.

Depending on the position within the tunnel system, they took samples from the ground that was influenced by precipitation or the salty water of the Baltic Sea. Their hypothesis is that the communities of organisms are fed from the Earth's surface. The team compared the concentration andmolecular composition of DOM along with stable and radiogenic carbon and water isotope levels, water chemistry and microbial community structure in fissure water samples of different depths, ages, and origins.

Even though the chemistry of the Groundwaters was completely different, a core Microbiome can always be found.

The creation of a core microbiome was triggered by the dominant supply of hard to digest organic matter.

We are only scratching the surface when it comes to the importance of the DOM. We were able to show that a multi-method approach can yield new insights. Microbiologists, geologists and chemists come together to combine their expertise.

More information: Helena Osterholz et al, Terrigenous dissolved organic matter persists in the energy-limited deep groundwaters of the Fennoscandian Shield, Nature Communications (2022). DOI: 10.1038/s41467-022-32457-z Journal information: Nature Communications Provided by Leibniz-Institut für Ostseeforschung Warnemünde