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J. Bacteriol., Nov 1996, 6539-6545, Vol 178, No. 22
SF Goldstein, KF Buttle and NW Charon
Spirochetes are an evolutionary and structurally unique group of bacteria.
Outermost is a membrane sheath (OS), and within this sheath are the
protoplasmic cell cylinder (PC) and periplasmic flagella (PFs). The PFs are
attached at each end of the PC and, depending on the species, may or may
not overlap in the center of the cell. The precise location of the PFs
within the spirochetal cells is unknown. The PFs could lie along the cell
axis. Alternatively, the PFs could wrap around the PC in either a right- or
a left-handed sense. To understand the factors that cause the PFs to
influence cell shape and allow the cells to swim, we determined the precise
location of the PFs in the Leptospiraceae (Leptonema illini) and Borrelia
burgdorferi. Our approach was to use high-voltage electron microscopy and
analyze the three-dimensional images obtained from thick sections of
embedded cells. We found that a single PF in L. illini is located in a
central channel 29 nm in diameter running along the helix axis of the
right- handed PC. The presence of the PFs is associated with the end being
hook shaped. The results obtained agree with the current model of
Leptospiraceae motility. In B. burgdorferi, which forms a flattened wave,
the relationship between the PFs and the PC is more complicated. A
multistrand ridge 67 nm in diameter, which was shown to be composed of PFs
by cross-sectional and mutant analysis, was found to extend along the
entire length of the cell. We found that the PFs wrapped around the PC in a
right-handed sense. However, the PFs formed a left- handed helix in space.
The wavelength of the cell body and the helix pitch of the PFs were found
to be identical (2.83 microm). The results obtained were used to propose a
model of B. burgdorferi motility whereby backward-propagating waves, which
gyrate counterclockwise as viewed from the back of the cell, are generated
by the counterclockwise rotation of the internal PFs. Concomitant with this
motion, the cell is believed to rotate clockwise about the body axis as
shown for the Leptospiraceae.
Copyright © 1996, American Society for Microbiology
Structural analysis of the Leptospiraceae and Borrelia burgdorferi by high-voltage electron microscopy
Department of Genetics and Cell Biology, University of Minnesota, St. Paul 55108, USA.
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