Swimming in a pool of syrup would be difficult for most people, but for bacteria like E. coli, it's easier than swimming in water. Scientists have known for decades that these cells move faster and farther in viscoelastic fluids, such as the saliva, mucus, and other bodily fluids they are likely to call home, but didn't understand why. Now, researchers from the University of Pennsylvania (Penn) School of Engineering and Applied Science and the Penn School of Arts & Sciences have come together to find an answer. Their findings could inform disease models and treatments, or even help design microscopic swimming robots. The study was led by Paulo Arratia, Ph.D., an Associate Professor in the Department of Mechanical Engineering and Applied Mechanics at Penn Engineering, and lab member Alison Patteson, a graduate student. Postdoctoral researcher Arvind Gopinath, Ph.D., a member of the Arratia lab, and Mark Goulian, Ph.D., the Edmund J. and Louise W. Kahn Endowed Term Professor of Biology in Penn Arts & Sciences, contributed to the study, which was published online on October 28, 2015 in an open-access article in Scientific Reports. The article is titled “Running and Tumbling with E. coli in Polymeric Solutions.” Experiments in the 1970s showed that, when in water, E. coli demonstrated what is known as "run and tumble" swimming. A bacterium would swim in a straight line, then tumble, or change direction in a random way. This is a good strategy for finding food, but it was unclear how that strategy would change in the more gelatinous fluids that E. coli tend to live in. "What's different now is that we can characterize the material properties of these fluids more precisely," Patteson said, "so we can connect changes in those properties to changes in the swimming behavior of the cells in a very systematic way.
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