A Screw-like Mechanism of Bacterial Motion

BPJ_111_5.c1.inddBacterial gliding is defined as steady movement of bacteria that have neither flagella nor pili, over a surface. It is an active process that requires a constant influx of energy. Using a mobile adhesin, SprB, and a powerful rotary motor that is fuelled by a proton motive force, gliding bacteria can move over surfaces with speeds reaching about 2 µm/s.

Adhesion to a surface and gliding motility are important during the development of some early biofilms. Gliding bacteria form biofilms over diverse surfaces. The human oral cavity (gingival region), scales of fishes, and plant roots are examples of environmental niches where some gliding bacteria colonize. The exact mechanism of gliding is not clear. To help understand gliding, we tracked both the motion of SprB and of a gliding bacterium in three-dimensional (3D) space.

Our cover image for the September 6 issue of Biophysical Journal shows the 3D track of SprB moving along the surface of a cell. A gold nanoparticle was coated with anti-SprB antibody and was attached to SprB. The nanoparticle was imaged using an evanescent field. An arrow and a dot represent the beginning and end of the track, respectively. As is evident from the track, SprB moves along an irregular right-handed spiral. The color of the track represents the position of SprB along the long axis of the cell. The track was plotted using MATLAB and was converted to an image file. Further, we showed that the spiral motion of SprB resulted in the screw-like motion of a gliding bacterium (i.e., cells rolled along their long axis as they moved forward). This information was used to propose a mechanism for gliding. While we need to learn more about the molecular details that govern gliding, we now know by 3D tracking that an adhesive external thread, which is localized as a right-handed spiral on the surface of a gliding cell, enables the movement of the cell in a screw-like fashion.

– Abhishek Shrivastava, Thibault Roland, Howard C. Berg

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