Borrelia burgdorferi periplasmic flagella have both skeletal and motility functions

Abstract

Bacterial shape usually is dictated by the peptidoglycan layer of the cell wall. In this paper, we show that the morphology of the Lyme disease spirochete Borrelia burgdorferi is the result of a complex interaction between the cell cylinder and the internal periplasmic flagella. B. burgdorferi has a bundle of 7-11 helically shaped periplasmic flagella attached at each end of the cell cylinder and has a flat-wave cell morphology. Backward moving, propagating waves enable these bacteria to swim in both low viscosity media and highly viscous gel-like media. Using targeted mutagenesis, we inactivated the gene encoding the major periplasmic flagellar filament protein FlaB. The resulting flaB mutants not only were nonmotile, but were rod-shaped. Western blot analysis indicated that FlaB was no longer synthesized, and electron microscopy revealed that the mutants were completely deficient in periplasmic flagella. Wild-type cells poisoned with the protonophore carbonyl cyanide-m-chlorophenylhydrazone retained their flat-wave morphology, indicating that the periplasmic flagella do not need to be energized for the cell to maintain this shape. Our results indicate that the periplasmic flagella of B. burgdorferi have a skeletal function. These organelles dynamically interact with the rodshaped cell cylinder to enable the cell to swim, and to confer in part its flat-wave morphology.spirochete ͉ Lyme disease ͉ allelic exchange ͉ morphology S pirochetes have a unique position among the bacteria. These motile bacteria are one of the few bacterial phyla that can be identified by both 16S ribosomal RNA sequence analysis and morphology (1). Outermost is a membrane sheath, and within this sheath are the cell cylinder and periplasmic flagella. A given periplasmic flagellum is attached subterminally at only one end of the cell cylinder, and it resides within the periplasmic space (2). Depending on the species, the cell morphology is either a helix, a flat wave, or an irregularly shaped helix (2-4). The size of the spirochete, the number of periplasmic flagella attached at each end, and whether the filaments overlap at the center of the cell varies from species to species (2, 5). This phylum contains many medically important bacteria including Treponema pallidum (syphilis), several Borrelia species (relapsing fever), Borrelia burgdorferi (Lyme disease), Leptospira interrogans (leptospirosis), Brachyspira sp. (human diarrheal disease, swine dysentery), and oral treponemes associated with periodontal disease (5-8).The periplasmic flagella of spirochetes have been characterized in detail. Genetic evidence, including targeted mutagenesis studies in Treponema denticola and Brachyspira hyodysenteriae, have shown that these organelles are directly involved in motility (9, 10) (C. Li and N.W.C., unpublished observations). By analyzing protruding periplasmic flagella from certain motility mutants of T. phagedenis, and from stationary-phase cells of several spirochete species, these organelles have been shown to rotate in a manner similar to th...

Overexpression of CsrA (BB0184) Alters the Morphology and Antigen Profiles ofBorrelia burgdorferi

“…This differential regulation could be significant in microenvironments such as the skin of a mammalian host where increased expression of adhesins such as DbpA or BBK32 may facilitate greater colonization capability in conjunction with reduced motility. The reduced levels of CsrA, favoring increased expression of FlaB, may provide an added advantage to the spirochetes under conditions requiring increased motility with a concomitant decrease in adherence (56,57). This initial characterization of the role of CsrA in regu-lating gene expression will help facilitate a better understanding of the mechanism and role of this potential global regulator in controlling the levels of pathophysiological determinants of B. burgdorferi that contribute to its survival and virulence in diverse hosts.…”

Borrelia burgdorferi Uniquely Regulates Its Motility Genes and Has an Intricate Flagellar Hook-Basal Body Structure

“…These PFs extend inward along the cell cylinder beneath an outer membrane sheath (6,24,28,46). B. burgdorferi PFs have a structure similar to that of flagella of other bacteria; a PF is composed of a basal body, a hook, and a filament containing a single major flagellin (FlaB) and a minor flagellin (FlaA) (6,21,28).…”

“…The location of FlaA in B. burgdorferi is unknown, but preliminary evidence indicates that this protein is on the surface of a PF proximal to the basal body (S. Satoshi, M. Motaleb, S. Aizawa, and N. W. Charon, unpublished data). Not only are the PFs essential for motility, but these structures are also critical in providing the characteristic flat-wave morphology of the intact spirochete (46,59). Rotation of the PF bundles in opposite directions, as viewed along a PF from its distal end to where it inserts into the cell cylinder, generates backward-moving waves along the cell body that propel the cell forward (12,24,25,38).…”

“…Recently, Motaleb et al described a targeted mutant with a mutation in the major flagellin gene flaB that did not synthesize PFs, was nonmotile, and was rod shaped (46). The only putative motility and chemotaxis protein that did not accumulate at wild-type levels in this mutant was the minor filament protein FlaA; the decrease in the level of FlaA, however, in the flaB mutant was found to occur at the posttranscriptional level (49).…”

Characterization of secA-sod operon in Borrellia burgdorferi.

“…Motility in spirochetes is achieved by internal organelles called endoflagella that are inserted at each pole and wrap around the protoplasmic cylinder (Holt, 1978;Motaleb et al, 2000). Endoflagella are structurally similar to the external flagella found in other eubacteria.…”