Flagellar Systems in Bacterial Pathogenicity

Bacterial flagellar systems are intricate supramolecular machines that impart motility and serve multifaceted roles in infection. Each flagellum comprises a membrane-embedded basal body, a flexible hook acting as a universal joint and a helical filament built from flagellin subunits. Rotation of the basal body, driven by ion gradients, transmits torque through the hook to the filament, enabling propulsion and directional switching. Beyond locomotion, flagella mediate adhesion to host tissues, secrete virulence factors, contribute to biofilm formation and trigger host immune responses. Post-translational modifications such as methylation and glycosylation modulate surface hydrophobicity, adhesion strength and immune evasion. High-resolution structural studies and biochemical analyses have revealed inter-domain connectivity, dynamic assembly mechanisms and even enzymatic functions of flagella, underscoring their evolutionary adaptation to diverse host environments. The potent immunogenicity of flagellin underpins its application as a vaccine adjuvant, while unique assembly pathways and modification enzymes represent promising targets for novel antimicrobials. Insights into flagellar architecture and regulation are thus central to understanding bacterial pathogenicity and devising global strategies for infection control.

Research from Nature Portfolio

Studies of flagellin methylation in Salmonella Typhimurium have shown that lysine methylation by the FliB methylase increases filament surface hydrophobicity, enhances adhesion to epithelial cells and phosphatidylcholine vesicles, and improves gut colonisation efficiency in vivo. Discovery of a proteolytic flagellin family bearing metallopeptidase insertions has revealed that certain Clostridium species assemble flagellar filaments with extracellular protease activity, facilitating host-protein degradation and tissue invasion. High-resolution cryo-EM of the native supercoiled hook has elucidated how alternating compression and extension of 11 protofilaments confer bending flexibility and torsional rigidity, enabling efficient torque transmission and directional control essential for bacterial swimming and host penetration.

Flagellar Systems in Bacterial Pathogenicity publication trend

The graph below shows the total number of articles in flagellar systems in bacterial pathogenicity across all publications each year (not limited to Nature Index journals).

Technical terms

Flagellum: A multi-protein motility organelle comprising a basal body, hook and filament that enables bacterial propulsion.

Basal body: The membrane-embedded rotary motor and export apparatus anchoring the flagellum to the cell envelope.

Hook: A short, curved structure acting as a universal joint to transmit torque between the basal body and filament.

Filament: A helical propeller formed by polymerised flagellin subunits, responsible for thrust generation.

Flagellin: The principal protein building block of the filament, often immunogenic and subject to post-translational modification.

Type III export system: A specialised secretion machinery that orchestrates the ordered export and assembly of flagellar components.

Post-translational modification: Chemical alterations of proteins after synthesis, such as methylation or glycosylation, affecting function and interactions.

Flagellinolysin: A class of flagellin proteins containing metallopeptidase domains that confer extracellular proteolytic activity.

Protofilament: A longitudinal chain of flagellin subunits within the filament, whose conformational shifts govern filament supercoiling.

References

1. Methylation of Salmonella Typhimurium flagella promotes bacterial adhesion and host cell invasion. Nature Communications (2020).
2. Discovery of a proteolytic flagellin family in diverse bacterial phyla that assembles enzymatically active flagella. Nature Communications (2017).
3. Structure of the native supercoiled flagellar hook as a universal joint. Nature Communications (2019).
4. An unbroken network of interactions connecting flagellin domains is required for motility in viscous environments. PLOS Pathogens (2023).
5. Bacterial Flagellar Filament: A Supramolecular Multifunctional Nanostructure. International Journal of Molecular Sciences (2021).
6. Structural and Functional Comparison of Salmonella Flagellar Filaments Composed of FljB and FliC. Biomolecules (2020).