1.2.1 Motile Fraction
When observing the wild-type Leptospira cells under a microscope,
you will find motile cells and non-motile ones, no matter what
species and serovars. The fraction of motile cells can be assessed
easily just by counting the numbers of motile and non-motile cells,
which is useful as the first quantitative evaluation of motility. Since
directional movements (i.e., swimming and crawling) of leptospires
involve coordination between two PFs, some cells show rotation
without net migration (Fig. 2). Such rotation cells are “non-translation cells” but should be discriminated from non-motile cells.
Thus, whether the cell rotate is a significant evaluation criterion.
1.2.2 Velocity
of Translation
The velocities of swimming and crawling of individual cells are
obtained by tracking the centroid of a cell body. When the cells
are recorded at 30 frames per second (so-called video rate), the cell
is assumed to move straight for 1/30 s.
1.2.3 Reversal
Frequency
Leptospira cells frequently reverse the swimming and crawling
direction. The reversal would be caused by switching of the rotational direction of the flagellar motor between counterclockwise
Fig. 2 Variation of the Leptospira morphology. Spiral-end is a left-handed spiral, generating thrust by
counterclockwise (CCW) gyration when being viewed from hook-end to spiral-end, whereas the right-handed
PC rotate clockwise (CW) for propelling a cell. Cells exhibiting spiral-hook or hook-spiral morphology translate
with the anterior spiral and the posterior hook. Spiral-spiral and hook-hook cells rotate at one position without
translation
Motility assays for Leptospira
141
When observing the wild-type Leptospira cells under a microscope,
you will find motile cells and non-motile ones, no matter what
species and serovars. The fraction of motile cells can be assessed
easily just by counting the numbers of motile and non-motile cells,
which is useful as the first quantitative evaluation of motility. Since
directional movements (i.e., swimming and crawling) of leptospires
involve coordination between two PFs, some cells show rotation
without net migration (Fig. 2). Such rotation cells are “non-translation cells” but should be discriminated from non-motile cells.
Thus, whether the cell rotate is a significant evaluation criterion.
1.2.2 Velocity
of Translation
The velocities of swimming and crawling of individual cells are
obtained by tracking the centroid of a cell body. When the cells
are recorded at 30 frames per second (so-called video rate), the cell
is assumed to move straight for 1/30 s.
1.2.3 Reversal
Frequency
Leptospira cells frequently reverse the swimming and crawling
direction. The reversal would be caused by switching of the rotational direction of the flagellar motor between counterclockwise
Fig. 2 Variation of the Leptospira morphology. Spiral-end is a left-handed spiral, generating thrust by
counterclockwise (CCW) gyration when being viewed from hook-end to spiral-end, whereas the right-handed
PC rotate clockwise (CW) for propelling a cell. Cells exhibiting spiral-hook or hook-spiral morphology translate
with the anterior spiral and the posterior hook. Spiral-spiral and hook-hook cells rotate at one position without
translation
Motility assays for Leptospira
141