Geologic Activity Lets Microbes Mingle Deep Underground

Geologic Activity Lets Microbes Mingle Deep Underground

Even a mile below the surface, our planet is alive with microbes. Scientists have long believed that these subterranean microbes , which live in aquifers or geothermal wells saw little ecological change. Recent research has shown that their populations are quite dynamic and shift species composition within days, rather than centuries. This could be due to geologic activity such as when rocks are split from compression or expanded.

Virals and bacteria living below the Earth’s surface are protected from environmental disruptors like solar radiation, weather changes and meteorite strikes. They tend to develop and grow slowly because they have limited access to nutrients. Yuran Zhang, an energy resource engineer at Stanford University, had been studying the flow of water between geothermal wells when she came up with the idea of using microbes to trace the flow. She and her team believed that microbial DNA could be used to identify each aquifer’s water source, as subterranean water pockets are often isolated from one another. Zhang said that they had access to these valuable samples of water through ongoing engineering work. It worked .”

For a study in the Proceedings of the National Academy of Sciences USA, Zhang and her team analyzed water from three boreholes connected to underground aquifers. They took samples once a week over 10 months, sequencing the DNA in each to determine which microbes were present. It seemed that each tiny ecosystem’s microbes were already set in stone at first. The researchers were surprised to discover that these signatures changed quickly after a rock-fracturing incident created cracks at the sampling location.

The team quickly realized that fracturing events can completely disrupt an aquifer’s microbial ecology within days by opening and closing tiny channels between isolated water pockets. “Our results are fascinating because they present not just a different mechanism to community assembly, but also a faster mechanism,” said Anne Dekas (a Stanford microbiologist).

This discovery is exciting, says University of Colorado geomicrobiologist Alexis Templeton, who was not involved in the new research: “There aren’t a lot of studies yet that really understand how water is moving through subsurface environments and how it affects the microbiology.”

Such research could help scientists determine how to store potentially dangerous materials like carbon dioxide and nuclear waste, Dekas states. It could also aid in the search of extraterrestrial life because similar hard rock aquifers are believed to be found on watery moons like Jupiter’s Europa.

It can be tempting to see geology as a separate entity from the realms of life. But according to Templeton, studies like this one “show us how intimately linked the two are.”

This article was originally published with the title “Microbe Mixer” in Scientific American 327, 5, 20-21 (November 2022)

doi: 10. 1038/scientificamerican1122-20b

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