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Journal of Bacteriology, August 1999, p. 4825-4833, Vol. 181, No. 16
Microbiology Unit, Department of
Biochemistry, University of Oxford, Oxford OX1 3QU, United
Kingdom1; Rowland Institute of
Science, Cambridge, Massachusetts 021422; and
Department of Chemical Engineering, University of Virginia,
Charlottesville, Virginia 22903-24423
Received 1 March 1999/Accepted 3 June 1999
Rhodobacter sphaeroides is a photosynthetic bacterium
which swims by rotating a single flagellum in one direction,
periodically stopping, and reorienting during these stops.
Free-swimming R. sphaeroides was examined by both
differential interference contrast (DIC) microscopy, which allows the
flagella of swimming cells to be seen in vivo, and tracking microscopy,
which tracks swimming patterns in three dimensions. DIC microscopy
showed that when rotation stopped, the helical flagellum relaxed into a
high-amplitude, short-wavelength coiled form, confirming previous
observations. However, DIC microscopy also revealed that the coiled
filament could rotate slowly, reorienting the cell before a transition back to the functional helix. The time taken to reform a functional helix depended on the rate of rotation of the helix and the length of
the filament. In addition to these coiled and helical forms, a third
conformation was observed: a rapidly rotating, apparently straight
form. This form took shape from the cell body out and was seen to form
directly from flagella that were initially in either the coiled or the
helical conformation. This form was always significantly longer than
the coiled or helical form from which it was derived. The resolution of
DIC microscopy made it impossible to identify whether this form was
genuinely in a straight conformation or was a low-amplitude,
long-wavelength helix. Examination of the three-dimensional swimming
pattern showed that R. sphaeroides changed speed while
swimming, sometimes doubling the swimming speed between stops. The rate
of acceleration out of stops was also variable. The transformations in
waveform are assumed to be torsionally driven and may be related to the
changes in speed measured in free-swimming cells. The roles of and
mechanisms that may be involved in the transformations of filament
conformations and changes in swimming speed are discussed.
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Transformations in Flagellar Structure of
Rhodobacter sphaeroides and Possible Relationship to Changes
in Swimming Speed
*
Corresponding author. Mailing address: Microbiology
Unit, Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom. Phone: 44 1865 275299. Fax: 44 1865 275297. E-mail: armitage{at}bioch.ox.ac.uk.
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