The Vibrio H-Ring Facilitates the Outer Membrane Penetration of the Polar Sheathed Flagellum

Abstract

The bacterial flagellum has evolved as one of the most remarkable nanomachines in nature. It provides swimming and swarming motilities that are often essential for the bacterial life cycle and pathogenesis. Many bacteria such as and species use flagella as an external propeller to move to favorable environments, whereas spirochetes utilize internal periplasmic flagella to drive a serpentine movement of the cell bodies through tissues. Here, we use cryo-electron tomography to visualize the polar sheathed flagellum of with particular focus on a-specific feature, the H-ring. We characterized the H-ring by identifying its two components FlgT and FlgO. We found that the majority of flagella are located within the periplasmic space in the absence of the H-ring, which are different from those of external flagella in wild-type cells. Our results not only indicate the H-ring has a novel function in facilitating the penetration of the outer membrane and the assembly of the external sheathed flagella but also are consistent with the notion that the flagella have evolved to adapt highly diverse needs by receiving or removing accessary genes. Flagellum is the major organelle for motility in many bacterial species. While most bacteria possess external flagella, such as the multiple peritrichous flagella found in and or the single polar sheathed flagellum in spp., spirochetes uniquely assemble periplasmic flagella, which are embedded between their inner and outer membranes. Here, we show for the first time that the external flagella in can be changed as periplasmic flagella by deleting two flagellar genes. The discovery here may provide new insights into the molecular basis underlying assembly, diversity, and evolution of flagella.

In Situ Structures of Polar and Lateral Flagella Revealed by Cryo-Electron Tomography

“…The Vibrio T-ring is composed of two proteins, MotY and MotX, while FlgT is a component of the H-ring (31)(32)(33). Homologs of MotX and FlgT are not identified in P. aeruginosa, but a MotY (PA3526) homolog is encoded (21).…”

Phylogenetic Distribution, Ultrastructure, and Function of Bacterial Flagellar Sheaths

“…One such embellishment is the H-ring, which is closely associated with the L-ring/P-ring complex and in close proximity to the outer membrane in Vibrio species [30,33]. The H-ring is located on the periplasmic side of the outer membrane, and the proteins that comprise the H-ring (FlgO and FlgT) have been identified [30,83,84]. Zhu and co-workers demonstrated that deletion of flgO or flgT in V. alginolyticus disrupted formation of the H-ring and resulted in a many of the flagella being located in the periplasm [84].…”

“…The H-ring is located on the periplasmic side of the outer membrane, and the proteins that comprise the H-ring (FlgO and FlgT) have been identified [30,83,84]. Zhu and co-workers demonstrated that deletion of flgO or flgT in V. alginolyticus disrupted formation of the H-ring and resulted in a many of the flagella being located in the periplasm [84]. About 80% of the flagella in the flgT mutant were located in the periplasm, compared with about 10% of the flagella in the flgO mutant and none of the flagella in the parental strain having a periplasmic location [84].…”

The flagellar motor ofVibrio alginolyticusundergoes major structural remodeling during rotational switching

“…Sample Preparation. The methods of sample preparation, data collection, data processing and subtomogram analysis were followed as described previously (Zhu et al, 2018). V. alginolyticus cells were cultured overnight at 30°C on VC medium and diluted 100 X with fresh VPG medium and cultured at 30°C.…”

“…Different from E. coli and Salmonella, Vibrio alginolyticus possesses several Vibrio-specific features: H, T, and O-rings. The O-ring is located on the outside of the outer membrane (Zhu et al, 2017), the H-ring facilitates the outer membrane penetration of the flagellum (Terashima et al, 2010;Zhu et al, 2018), and the Tring contacts the H-ring and stators, presumably acting as a scaffold to hold the stators Zhu et al, 2019). Flagellar rotation is powered by an electrochemical gradient across the cell membrane that drives ion flow through the stator complex (Berg, 2003;Kojima and Blair, 2004;Li et al, 2011;Terashima et al, 2008).…”