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Journal of Bacteriology, January 1999, p. 600-609, Vol. 181, No. 2
Departments of Molecular and Cellular
Biology1 and
Mathematics,2 University of Arizona,
Tucson, Arizona 85721-0106
Received 22 July 1998/Accepted 27 October 1998
The swimming motions of cells within Bacillus subtilis
colonies, as well as the associated fluid flows, were analyzed from video films produced during colony growth and expansion on wet agar
surfaces. Individual cells in very wet dense populations moved at rates
between 76 and 116 µm/s. Swimming cells were organized into patterns
of whirls, each approximately 1,000 µm2, and jets of
about 95 by 12 µm. Whirls and jets were short-lived, lasting
only about 0.25 s. Patterns within given areas constantly repeated
with a periodicity of approximately 1 s. Whirls of a given
direction became disorganized and then re-formed, usually into whirls
moving in the opposite direction. Pattern elements were also organized
with respect to one another in the colony. Neighboring whirls
usually turned in opposite directions. This correlation decreased as a
function of distance between whirls. Fluid flows associated with
whirls and jets were measured by observing the movement of marker latex
spheres added to colonies. The average velocity of markers traveling in
whirls was 19 µm/s, whereas those traveling in jets moved at 27 µm/s. The paths followed by markers were aligned with the direction
of cell motion, suggesting that cells create flows moving with them
into whirls and along jets. When colonies became dry, swimming motions
ceased except in regions close to the periphery and in isolated islands
where cells traveled in slow whirls at about 4 µm/s. The addition of
water resulted in immediate though transient rapid swimming (> 80 µm/s) in characteristic whirl and jet patterns. The rate of swimming
decreased to 13 µm/s within 2 min, however, as the water diffused
into the agar. Organized swimming patterns were nevertheless preserved
throughout this period. These findings show that cell swimming in
colonies is highly organized.
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Organized Cell Swimming Motions in Bacillus
subtilis Colonies: Patterns of Short-Lived Whirls and
Jets
*
Corresponding author. Mailing address: Department of
Molecular and Cellular Biology, University of Arizona, Life Sciences South Building, P.O. Box 210106, Tucson, AZ 85721-0106. Phone: (520)
621-3617. Fax: (520) 621-3709. E-mail:
nhm{at}u.arizona.edu.
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