Under the Boise River, a metropolis comes alive

Next time you walk along the Boise River, look past the water at the sand and gravel below. Under the surface lies a chaotic network of microscopic hallways that function like a bustling city. Within this sponge-like world, trillions of bacteria hunker down to build their houses, forming adhesive communities known as biofilms. These bacteria play an important role in our waterways. They filter and clean chemicals that can leach into the water.

Kevin Roche, assistant professor of civil engineering, said, "The river's sediments are complex. If you were to zoom in, it would be like you're walking through a chaotic set of hallways. There are many intermingling pathways, and each of them varies: short or long, with various doors and detours. The stuff I really like to think about is who is opening and closing those doors."

These bacteria are microscopic, organized metropolises. Roche explains that these organisms engage in a "giant game of telephone" within river sediments. When one group of bacteria grows large enough to fill the space between sediments, they close the door, shifting the water flow and signaling other bacteria far away to react. They even communicate using a universal language called Autoinducer-2, a "bacterial Esperanto," or mutual language, that allows different species to coordinate their decisions.

This microscopic city serves a vital purpose: it acts as the "river's liver," Roche said, because, like a liver that serves to filter our blood, these bacteria clean our water by "eating" or "breathing" contaminants we can't see, such as nitrates from fertilizer, trace pharmaceuticals, or antibiotics that leach into the water through livestock urination, evading standard treatment plants. However, while it's important to have this natural bacteria working so hard to clean our river, this natural filtration has a catch. As they process our waste, they can breathe out greenhouse gases like nitrous oxide.

By using actual Boise River sediment in his lab, Roche is observing these cities to learn more about their function, which, someday, may lead to finding the "sweet spot" where the river cleans the water without the environmental cost. His work is so universal that it even translates to how bacteria thrive in the human gut, something he will be looking at more closely in the future. "We need to zoom in before we see the whole picture," Roche said.

This material is based upon work supported by the U.S. National Science Foundation under award No. 2347707. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the U.S. National Science Foundation.

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