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Journal of Bacteriology, November 1998, p. 5978-5983, Vol. 180, No. 22
School of Biology, Georgia Institute of
Technology, Atlanta, Georgia 30332-0230
Received 5 June 1998/Accepted 10 September 1998
Data on the shapes of 218 genera of free-floating or free-swimming
bacteria reveal groupings around spherical shapes and around rod-like
shapes of axial ratio about 3. Motile genera are less likely to be
spherical and have larger axial ratios than nonmotile genera. The
effects of shape on seven possible components of biological fitness
were determined, and actual fitness landscapes in phenotype space are
presented. Ellipsoidal shapes were used as models, since their
hydrodynamic drag coefficients can be rigorously calculated in the
world of low Reynolds number, where bacteria live. Comparing various
shapes of the same volume, and assuming that departures from spherical
have a cost that varies with the minimum radius of curvature, led to
the following conclusions. Spherical shapes have the largest random
dispersal by Brownian motion. Increased surface area occurs in oblate
ellipsoids (disk-like), which rarely occur. Elongation into prolate
ellipsoids (rod-like) reduces sinking speed, and this may explain why
some nonmotile genera are rod-like. Elongation also favors swimming
efficiency (to a limited extent) and the ability to detect stimulus
gradients by any of three mechanisms. By far the largest effect
(several hundred-fold) is on temporal detection of stimulus gradients,
and this explains why rod-like shapes and this mechanism of chemotaxis
are common.
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Fitness Landscapes for Effects of Shape on
Chemotaxis and Other Behaviors of Bacteria
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Mailing address: School of Biology, Georgia Institute
of Technology, Atlanta, GA 30332-0230. Phone: (404) 894-8426. Fax:
(404) 894-0519. E-mail:
david.dusenbery{at}biology.gatech.edu.
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