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

Abstract

Borrelia burgdorferi is a flat-wave, motile spirochete that causes Lyme disease. Motility is provided by periplasmic flagella (PFs) located between the cell cylinder and an outer membrane sheath. The structure of these PFs, which are composed of a basal body, a hook, and a filament, is similar to the structure of flagella of other bacteria. To determine if hook formation influences flagellin gene transcription in B. burgdorferi, we inactivated the hook structural gene flgE by targeted mutagenesis. In many bacteria, completion of the hook structure serves as a checkpoint for transcriptional control of flagellum synthesis and other chemotaxis and motility genes. Specifically, the hook allows secretion of the anti-sigma factor FlgM and concomitant late gene transcription promoted by 28 . However, the control of B. burgdorferi PF synthesis differs from the control of flagellum synthesis in other bacteria; the gene encoding 28 is not present in the genome of B. burgdorferi, nor are any 28 promoter recognition sequences associated with the motility genes. We found that B. burgdorferi flgE mutants lacked PFs, were rod shaped, and were nonmotile, which substantiates previous evidence that PFs are involved in both cell morphology and motility. Although most motility and chemotaxis gene products accumulated at wild-type levels in the absence of FlgE, mutant cells had markedly decreased levels of the flagellar filament proteins FlaA and FlaB. Further analyses showed that the reduction in the levels of flagellin proteins in the spirochetes lacking FlgE was mediated at the posttranscriptional level. Taken together, our results indicate that in B. burgdorferi, the completion of the hook does not serve as a checkpoint for transcriptional regulation of flagellum synthesis. In addition, we also present evidence that the hook protein in B. burgdorferi forms a high-molecular-weight complex and that formation of this complex occurs in the periplasmic space.Borrelia burgdorferi, the causative agent of Lyme disease, is a spirochete with a characteristic flat-wave morphology (24, 25; for a review, see reference 12). As a result of their unusual morphology, B. burgdorferi and other spirochete species have a highly specialized ability that allows them to traverse viscous gellike media (8). This unique swimming ability enables these bacteria to penetrate into specific host connective tissues and ecological niches (43). The importance of motility as a virulence factor has been implicated in several spirochete species, including Treponema denticola (42), Brachyspira hyodysenteriae (54), Borrelia garinii (60), and B. burgdorferi (10, 56).Motility in B. burgdorferi is provided by bundles of between 7 and 11 periplasmic flagella (PFs) that are subterminally attached near the cell ends. 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 ...

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

“…at this juncture, it is interesting to speculate that the increased levels of CsrA Bb may downregulate the expression of genes of the flgK motility operon and thereby affect the stability of FlaB at the posttranscriptional levels. It has been previously demonstrated that there is a reduction in the levels of the flagellin proteins in the absence of the gene encoding the hook structural protein FlgE (71). The role of CsrA in motility and morphology has been reported for several other bacterial species.…”

Hypothetical Protein BB0569 Is Essential for Chemotaxis of the Lyme Disease Spirochete Borrelia burgdorferi

“…A protein turnover assay was carried out as previously described (37,38). Briefly, B. burgdorferi strains were grown in BSK-II medium at 34°C.…”

A Single-Domain FlgJ Contributes to Flagellar Hook and Filament Formation in the Lyme Disease Spirochete Borrelia burgdorferi

“…It is believed that motility plays a critical role in the biology of spirochetes and in the processes of diseases caused by pathogenic spirochetes (9,11,16,32,55). Spirochetes swim by means of two rotating bundles of periplasmic flagella (PFs) that reside between the outer membrane and cell cylinder (23,32,38,49). PFs are structurally similar to the flagella of other bacteria, as each consists of a basal body-motor complex, a hook, and a filament (27,33,34,43).…”

“…Approximately 7 to 11 PFs are subterminally attached at each cell end, and these organelles form a tightfitting ribbon that wraps around the cell cylinder (12,34). The PFs have both skeletal and motility functions (32,38,49); aflagellated mutants are nonmotile and rod-shaped, rather than having the flat-wave morphology. Motility is considered to be an important virulence factor of B. burgdorferi since motility-defective mutants fail to invade human tissues and establish mammalian infection (32,48).…”

“…Motility is considered to be an important virulence factor of B. burgdorferi since motility-defective mutants fail to invade human tissues and establish mammalian infection (32,48). Due to its medical importance and recent advances in genetic manipulations of B. burgdorferi (47,52), this organism has recently emerged as a model system to study the genetic regulation, structure, and assembly of PFs, as well as chemotaxis in spirochetes (11,12,32,34,39,41,49,60). In this report, a singledomain FlgJ homolog (FlgJ Bb ) was identified in the genome of B. burgdorferi.…”