By Hook or By Crook

Incoming Assistant Professor Jeff Guasto (Ph.D., Brown University) has been working on understanding how single-celled organisms, like bacteria, get around. Guasto, a postdoctoral researcher in MIT’s Department of Civil and Environmental Engineering, and his colleagues have been studying how microbes, such as marine bacteria, use their flagella to propel themselves forward, backward, and change direction. Researchers had observed the marine bacteria changing direction using a flicking motion of the flagellum, but they didn’t understand how it was happening.

Motile marine bacteria exploit a buckling instability of the flexible hook (green) at the base of their flagellum (yellow) to change swimming direction, turning what is otherwise a structural failure into a fundamental biological function. GRAPHIC: KWANGMIN SON, JEFFREY GUASTO, GLYNN GORICK AND ROMAN STOCKER

Using high-speed video shot a 1,000 frames per second, the MIT team was able to record the flicking motion of bacteria swimming forward. They determined that the flick occurs when the “hook,” a small flexible rod connecting the flagellum to the cell’s internal motor, buckles.

“A single actuator, the flagellum, enables both propulsion and turning in these bacteria,” Guasto says. “This is a well-known principle in robotics called ‘underactuation,’ but it is rarely considered at the micrometer scale.”

“The mechanism of turning by buckling represents one of the smallest examples in nature of a biological function stemming from controlled mechanical failure and reveals a new role for flexibility in biological materials, which could inspire new microrobotic solutions in medicine and engineering,” the authors say in their July 7 paper in Nature Physics.

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