Phylogenetic Distribution, Ultrastructure, and Function of Bacterial Flagellar Sheaths

Abstract

A number of Gram-negative bacteria have a membrane surrounding their flagella, referred to as the flagellar sheath, which is continuous with the outer membrane. The flagellar sheath was initially described in Vibrio metschnikovii in the early 1950s as an extension of the outer cell wall layer that completely surrounded the flagellar filament. Subsequent studies identified other bacteria that possess flagellar sheaths, most of which are restricted to a few genera of the phylum Proteobacteria. Biochemical analysis of the flagellar sheaths from a few bacterial species revealed the presence of lipopolysaccharide, phospholipids, and outer membrane proteins in the sheath. Some proteins localize preferentially to the flagellar sheath, indicating mechanisms exist for protein partitioning to the sheath. Recent cryo-electron tomography studies have yielded high resolution images of the flagellar sheath and other structures closely associated with the sheath, which has generated insights and new hypotheses for how the flagellar sheath is synthesized. Various functions have been proposed for the flagellar sheath, including preventing disassociation of the flagellin subunits in the presence of gastric acid, avoiding activation of the host innate immune response by flagellin, activating the host immune response, adherence to host cells, and protecting the bacterium from bacteriophages.

Lipopolysaccharide From E. coli Increases Glutamate-Induced Disturbances of Calcium Homeostasis, the Functional State of Mitochondria, and the Death of Cultured Cortical Neurons

“…Endotoxins, lipopolysaccharides (LPS) of the outer membrane and the flagellar sheath of gram-negative bacteria, are important virulence factors in bacterial infection ( Mook-Kanamori et al, 2011 ; Chu et al, 2020 ). LPS is commonly used both in the neuroinflammation in vitro models and in the LPS-induced neuroinflammation, depression and the LPS-evoked changes in absence epileptic activity in vivo ( Kovács et al, 2019 ; Ali et al, 2020 ).…”

Recent Advances in the Bacterial Flagellar Motor Study

“…All review articles provide both expert and non-expert readers with advances in understanding the structures and functions of the bacterial flagellum. They highlight the most recent observations and illustrate perspectives for future research [4][5][6][7][8][9][10][11][12][13].…”

“…The scope of this Special Issue is to cover recent advances in our understanding of the structures and functions of the bacterial flagellar motor derived from different bacterial species. This Special Issue includes ten review articles [ 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ] and eleven original research papers [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ] from well-known experts in the field.…”

Achievements in bacterial flagellar research with focus on Vibrio species

“…is covered by a sheath connected to the outer membrane. 114 Furthermore, the two ring structures, called the H-ring and T-ring, exist outside the LP-ring structure (Figure 7). The major component proteins of the H-ring were shown to be FlgT and FlgO; when the H-ring is absent, the flagellar filaments do not push up against the outer membrane to form a sheathed flagellum, but instead the filaments are built up periplasmically, as in the flagellum of spirochetes.…”