How bacteria swim

Swimming cells of the bacterium Desulfovibrio sapovorans.
Click on the picture to watch a short video clip (AVI file, 265 kB)
Swimming bacteria
Many bacteria are motile. Some (mainly large) bacteria creep along surfaces on a layer of mucus like little snails. Most motile bacteria have one or several flagella. These rotate like propellers in a kind of ball-bearing. Depending on their rotational direction the bacteria are pushed ahead or pulled backwards. At the same time, the bacteria are rotating, too, but slower than the flagella, and the other way around.
The impression of a snake-like movement is not caused by bending of the bacteria. The cells are rigid spirals that screw through the medium. The flagellum of a cell in the upper left corner gets stuck to the ground. After that the cell is turning on the spot.

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