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Category: Bacterial Pathogenesis
Architecture and Assembly of Periplasmic Flagellum, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781683670285/9781683670278_Chap16-1.gif /docserver/preview/fulltext/10.1128/9781683670285/9781683670278_Chap16-2.gifAbstract:
The flagellum is a major organelle for motility in many bacterial species. It confers locomotion and is often associated with virulence of bacterial pathogens. Flagella from different species share a conserved core but also exhibit profound variations in flagellar structure, flagellar number, and placement ( 1 , 2 ), resulting in distinct flagella that appear to be adapted to the specific environments that the bacteria encounter. While many bacteria possess multiple peritrichous flagella, such as those found in Escherichia coli and Salmonella enterica, other bacteria, such as Vibrio spp. and Pseudomonas aeruginosa, normally have a single flagellum at one cell pole ( Fig. 1 ). Spirochetes uniquely assemble flagella that are embedded in periplasmic space between their inner and outer membranes, thus called periplasmic flagella ( 3 ). Although the flagella of E. coli and Salmonella have been extensively studied for several decades, periplasmic flagella are less understood, despite their profound impact on the distinctive morphology and motility of spirochetes. In this chapter, many aspects of periplasmic flagella are discussed, with particular focus on their structure and assembly.
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Distinctive placement of bacterial flagellum. (A) Bacteria with flagella distributed all over the cell (e.g., Escherichia coli) are peritrichous. (B) Monotrichous bacteria, such as Vibrio cholerae, Pseudomonas aeruginosa, and Caulobacter crescentus, have a single flagellum present at one end of the cell. (C) Spirochetes, including species of Borrelia, Treponema, and Leptospira, possess specialized flagella located within the periplasmic space. The rotation of the periplasmic flagella allows the bacterium to swim forward in a corkscrew-like motion.
Comparison of motor structures from E. coli, Vibrio, H. pylori, and Borrelia. (A) A central section of an E. coli flagellar motor. (B) A central section from a nonsheathed Vibrio flagellar motor. (C) A central section from a sheathed Vibrio flagellar motor. (D) A central section from a sheathed flagellar motor of H. pylori. (E) A central section from a Borrelia flagellar motor. (F to J) Schematic models derived from the central sections shown in panels A to E, respectively. Adapted from prior publications ( 16 , 50 , 51 ), with permission.
Characterization of the unique features in periplasmic flagella, as examined through mutational analysis. (A) Central section from a mutant lacking FlbB. (B) Central section from a mutant lacking BB0236. (C) Central section from a class average of a mutant lacking FliL. (D) Central section from another class average of a mutant lacking FliL. (E) A central section from wild-type flagellar motor. (F to J) Schematic models derived from panels A to E, respectively. Adapted from a prior publication ( 17 ), with permission.
Comparison of the fT3SS from B. burgdorferi and the vT3SS from Salmonella. (A) A central section from the B. burgdorferi motor. (B) The fT3SS in the spirochete motor includes the ATPase complex (orange) and the export apparatus (purple) underneath the MS ring. (C and D) The vT3SS from the Salmonella injectisome is modeled in a similar color scheme. The difference between the two T3SSs is striking in a comparison of the cross sections of their ATPase complexes. Note that the C ring from the B. burgdorferi motor is a continuous ring with ∼46 copies of FliN tetramer. There are 23 visible FliH spokes (E and F). There are six pods in the Salmonella injectisome. Only six spokes of the FliH homolog OrgB connect the ATPase complex to the SpaO molecules that compose the pod of the injectisome. Adapted from a prior publication ( 52 ), with permission.