Rotating Bacteria on Solid Surfaces Without Tethering

Bacterial motion is strongly affected by the presence of a surface. One of the hallmarks of swimming near a surface is a defined curvature of bacterial trajectories, underlining the importance of counter rotations of the cell-body and flagellum for locomotion of the microorganism. We find that there is another mode of bacterial motion on solid surfaces, i.e., self trapping due to fluid flows created by a rotating flagellum perpendicular to the surface. For a rod-like bacterium, such as Escherichia coli, this creates a peculiar situation in that the bacterium appears to swim along a minor axis of the cell body and is pressed against the surface.

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