Bacteria’s tail spins make water droplets swirl

The way Bacillus subtilis bacteria swim in a single drop of water can spin the fluid into a spiraling vortex.

Josef Reischig/Wikimedia Commons (CC BY SA 3.0)

When bacteria band together, they can turn a fairly tame drop of water into a swirling vortex. The swirl is spun up by the bacteria’s tail-like flagella and the basic physics of how fluids flow, researchers report June 23 in the Proceedings of the National Academy of Sciences. The finding could enable scientists to control the collective motion of the microbes and possibly prevent the spread of infection in the human body, the researchers suggest.

In a droplet of water, bacteria start swimming in every direction. They collide with each other and then start circling the droplet in the same direction. But that synchronized swimming only lasts so long. The force from the flagella of bacteria at the outer edge of the droplet becomes so strong that the microbes on the inside can’t keep up: They ultimately have to go with the flow formed from the outer bacteria’s flagella and start swimming in the opposite direction, a pattern that swirls into a vortex.Brown Univ., Univ. of Cambridge

Ashley Yeager is the associate news editor at Science News. She has worked at The Scientist, the Simons Foundation, Duke University and the W.M. Keck Observatory, and was the web producer for Science News from 2013 to 2015. She has a bachelor’s degree in journalism from the University of Tennessee, Knoxville, and a master’s degree in science writing from MIT.

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