Buckling up to turn
Bacteria swim by rotating the helical, hairlike flagella that extend from their unicellular bodies. Some bacteria, including the Escherichia coli (E. coli) living in the human gut, have multiple flagella that rotate as a bundle to move the cell forward. These cells turn somewhat acrobatically by unbundling their flagella, causing the cell to tumble, reorient and strike out in another direction.But many microbes, including 90 percent of motile marine bacteria, have only a single rigid flagellum; they are able to swim both forward and backward by rotating this flagellum either counterclockwise or clockwise. These microbes change direction with a sideways “flick” of their lone flagellum — a flick first documented in 2011 as a unique swimming stroke whose mechanism has remained a mystery. Now, using high-speed video to record individual swimming bacteria at up to 1,000 frames per second, researchers at MIT have seen that the flick occurs when the...