| Speaker: | Stuart Goldstein ( Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, Minnesota) | |||
| Title: | The Motility of the Spirochete, Leptonema illni. |
| Abstract: |
Many bacteria swim by means of left-handed helical flagella that are rotated by basal motors embedded in the surface of the cell body. There are variations in the number and arrangement of these flagella among different bacteria. In the rod-shaped bacteria, such as E. coli, the flagella form a rotating bundle behind the cell body. When the flagella rotate counterclockwise (CCW) as seen from behind the cell, the cell swims forward; when they rotate clockwise (CW), the bundle is disrupted and the cell fails to advance. In the spirochetes, the flagella typically wind around the cell body.
Spirochetes have two bundles of flagella. The flagella are located between the cell wall and an outer membrane, in a region called the periplasmic space, and are referred to as periplasmic flagella (PFs). A bundle emerges near each end of the cell body and projects toward the opposite end. Depending on the species, the bundles may be long enough to overlap in the center of the cell or short enough to leave a central region that contains only the cell body. The cell body is helical in many spirochetes. In addition, the helical flagella affect the shape of the regions in which they reside, so that the shape of the cell can be fairly complex.
L. illini has a right-handed helical cell body and a single short PF at each end. The rotations of the cell body and of each flagellum can be observed. The shape of each PF depends on its direction of rotation: if it rotates CCW as seen from the center of the cell, it forms a left-handed helix, or spiral (S); if it rotates CW, it forms a planar hook (H). There are thus three combinations of end shapes: S-S, S-H and H-H. With the first, the cell swims through the medium with the S end leading; with the latter two, the rotations of the two ends cancel and the cell does not advance. In an S-S cell, as viewed from behind the cell, both flagella rotate CCW and the cell body rotates CW. Although qualitative descriptions of these rotations have been reported, there have not been quantitative measurements of rotation rates and swim speeds that could be compared with theoretical predictions. Measurements of these movements and refined descriptions of the geometry of these cells will be presented.
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