Buckling of appendage drives tiny two-point turn
K. Son et al/Nature Physics
When headed the wrong way, some bacteria turn by letting their propellers flop.
The newly discovered turning mechanism explains how a marine bacterium can control its direction using only a single flagellum, a stiff, rotating appendage that propels the cell forward. Turning depends on a mechanical characteristic that engineers might consider a failure if the flagellum were human-made: the tendency of flexible materials to buckle under pressure.
A multiflagellated bacterium like Escherichia coli turns by releasing one flagellum from a spinning bundle, which unwinds and sends the cell tumbling in a new direction. But 90 percent of mobile marine bacteria have only one flagellum each. In the past, scientists thought that these one-prop microbes could swim only in a straight line, says coauthor Roman Stocker of MIT. Then in 2011, a team led by Xiao-Lun Wu of the University of Pittsburgh showed that the single-flagellum bacterium Vibrio alginolyticus can make