Bacteria swim with flagella, and a clever switching system allows them to aim at a target. New research shows in more detail how the flagellar drive changes direction.

Many species of bacteria have one or more flagella. These long whip-like tails that rotate on their own axis allow them to move around, searching for nutrients in the environment or a victim to infect. The flagellum can quickly change its direction of rotation, which determines the bacterium’s course. Exactly how this switch works has been the subject of research for years.

In fact, flagella are a wonderful example of bio-nanotechnology because each flagellum is attached to a rotor: a ring-shaped, rotating protein complex with dozens of subunits. This enables the bacterial cell to convert the flow of protons via motor proteins into counterclockwise or clockwise rotation. The question is how exactly the rotor changes direction.

Two papers recently published in Nature Microbiology provide a clearer picture. A team led by Susan Lea from the UK and Tina Iverson from the US used an electron microscope to zoom in on the switching mechanism. They show how a small change in the shape of a protein determines the direction of rotation.