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J. Bacteriol. doi:10.1128/JB.01288-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The flat ribbon configuration of the periplasmic flagella of Borrelia burgdorferi and its relationship to motility and morphology

Department of Microbiology, Immunology and Cell Biology, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, WV 26506-9177; Department of Genetics, Cell Biology, and Development, 6-160 Jackson Hall, University of Minnesota, Minneapolis MN 55455; Resource for Visualization of Biological Complexity, Wadsworth Center, Empire State Plaza, Albany, NY 12201-0509; New York State Department of Health, Wadsworth Center, David Axelrod Institute, 120 New Scotland Avenue, Albany, NY 12208; Department of Microbiology and Immunology, Brody School of Medicine, East Carolina University, Greenville, NC 27834; Department of Cell Biology, University of Connecticut Health Center, Farmington, CT 06030-3505; Supercomputer Institute, 599 Walter Library, University of Minnesota, Minneapolis MN 55455

^* To whom correspondence should be addressed. Email: ncharon{at}hsc.wvu.edu.

	Abstract

Electron cryotomography was used to analyze the structure of the Lyme disease spirochete Borrelia burgdorferi. This methodology offers a new means for studying the native architecture of bacteria by eliminating the chemical fixing, dehydration, and staining steps of conventional electron microscopy. Using electron cryotomography, we noted membrane blebs formed at the ends of the cells. These blebs may be precursors to vesicles that are released from cells grown in vivo and in vitro. We found that the periplasmic space of B. burgdorferi was quite narrow (16.0 nm) compared that of Escherichia coli and Pseudomonas aeruginosa. However, in the vicinity of the periplasmic flagella, this space is considerably widened (42.3 nm). In contrast to previous results, the periplasmic flagella did not form a bundle, but rather a tight-fitting ribbon that wraps around the protoplasmic cell cylinder in a right-handed sense. We show how the ribbon configuration of the assembled periplasmic flagella is more advantageous than a bundle for both swimming and forming the flat-wave morphology. Previous results indicate that B. burgdorferi motility is dependent on the rotation of the periplasmic flagella in generating backward-moving waves along the length of the cell. This swimming requires that the rotation of the flagella exerts force on the cell cylinder. Accordingly, a ribbon is more beneficial than a bundle, as this configuration allows each periplasmic flagellum to have direct contact with the cell cylinder in order to exert that force, and it minimizes interference between the rotating filaments.