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Journal of Bacteriology, August 1998, p. 3923-3932, Vol. 180, No. 15
Max-Planck-Institut für Biochemie,
D-82152 Martinsried, Germany
Received 6 March 1998/Accepted 26 May 1998
The sheath of the filamentous, gliding cyanobacterium
Phormidium uncinatum was studied by using light
and electron microscopy. In thin sections and freeze fractures the
sheath was found to be composed of helically arranged
carbohydrate fibrils, 4 to 7 nm in diameter, which showed a substantial
degree of crystallinity. As in all other examined motile cyanobacteria,
the arrangement of the sheath fibrils correlates with the motion
of the filaments during gliding motility; i.e., the
fibrils formed a right-handed helix in clockwise-rotating species and a
left-handed helix in counterclockwise-rotating species and were
radially arranged in nonrotating cyanobacteria. Since sheaths could
only be found in old immotile cultures, the arrangement seems to depend
on the process of formation and attachment of sheath fibrils
to the cell surface rather than on shear forces created by the
locomotion of the filaments. As the sheath in P. uncinatum directly contacts the cell surface via the
previously identified surface fibril forming glycoprotein oscillin (E. Hoiczyk and W. Baumeister, Mol. Microbiol. 26:699-708, 1997), it seems
reasonable that similar surface glycoproteins act as platforms for the
assembly and attachment of the sheaths in cyanobacteria. In
P. uncinatum the sheath makes up
approximately 21% of the total dry weight of old cultures and consists
only of neutral sugars. Staining reactions and X-ray diffraction
analysis suggested that the fibrillar component is a homoglucan that is
very similar but not identical to cellulose which is cross-linked
by the other detected monosaccharides. Both the chemical composition
and the rigid highly ordered structure clearly distinguish the sheaths
from the slime secreted by the filaments during gliding motility.
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Structural and Biochemical Analysis of the Sheath
of Phormidium uncinatum
*
Present address: Laboratory of Cell Biology, The
Rockefeller University, 1230 York Ave., New York, NY 10021. Phone
(212) 327-8181. Fax: (212) 327-7880. E-mail:
Hoiczye{at}rockvax.rockefeller.edu.
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