To test their hypothesis that compression was responsible for the flicking process, Son and Guasto altered the concentration of sodium ions in the water. Because a sodium ion pump drives the cell's motor, decreasing the salt content slows the microbes, and thus decreases compressive forces on the hook, preventing the flick.
Altogether they studied the trajectories of more than 17,000 bacteria, including a coral pathogen and a mixed community of microbes from the Atlantic Ocean. All displayed the same swimming pattern, leading to the conclusion that this remarkable maneuver is a common means of reorientation for marine microbes.
"At first blush, one might think that a single polar flagellum is a more economical design than multiple flagella, especially since flagellar bundles are not very efficient," Howard Berg, the Herchel Smith Professor of Physics and professor of molecular and cellular biology at Harvard University, writes in an analysis published in the same issue of Nature Physics. "But most of the costs in this business are in the construction, not in the operation. Presumably, it's cheaper to place motors at random positions along the cell wall than it is to mount them on a specific platform at one pole. One benefit of the polar design might be enhanced swimming speeds; one cost a more constrained search paradigm. Nature appears to have stumbled upon a solution to the latter problem: a flick triggered by a buckling instability."
"The buckling of the hook of these bacteria is one of the smallest examples in nature of structural failure
|Contact: Denise Brehm|
Massachusetts Institute of Technology