Bacterial Flagellar Motor Mechanisms and Dynamics

The bacterial flagellar motor is a sophisticated, membrane-embedded nanomachine that powers the rotary displacement of helical filaments, enabling motility and environmental navigation across diverse bacterial species. It comprises a central rotor–stator assembly in which transmembrane stator units harness proton or sodium ion gradients to generate torque, driving continuous rotation of the rotor ring. This rotor is coupled via a flexible hook acting as a universal joint to the extracellular filament, converting rotary motion into thrust. Directional switching between counterclockwise and clockwise rotation is controlled by the cytoplasmic C ring, formed by FliG, FliM and FliN, which undergoes conformational changes in response to chemotactic signals. Stator units assemble and disassemble dynamically according to mechanical load, while symmetry mismatches between the MS ring and C ring influence torque efficiency and switching behaviour. Advances in high-resolution structural methods have resolved atomic architectures of core components, elucidating mechanisms of ion selectivity, torque generation and directional control. Insights into these processes carry significant implications for antimicrobials targeting motility and the engineering of biomimetic rotary devices. Current research continues to uncover the interplay between structural dynamics, energy transduction and signal integration that underpins flagellar motor function.

Research from Nature Portfolio

Recent studies have determined the structure of sodium-driven stator units by cryo-electron microscopy, revealing precise ion-binding sites and a dynamic helical motif in PomA that regulates stator activation and torque transmission. Electrostatic mapping has shown how hydrophobic residues in PomA prime the stator for unidirectional rotation and integrate the unit into the rotor. Complementary work on the MS ring has demonstrated that full-length FliF subunits assemble into a 34-meric ring with distinct 23- and 11-fold subsymmetries in its inner and middle regions. This symmetry architecture templates C-ring assembly and accommodates variable stator occupancy, clarifying how symmetry mismatch modulates motor performance. Together, these findings advance our mechanistic understanding of ion selectivity, stator–rotor coupling and symmetry-driven regulation in bacterial flagellar motors.

Bacterial Flagellar Motor Mechanisms and Dynamics publication trend

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

Technical terms

Stator: Transmembrane protein complex that couples ion flux to mechanical torque generation.

Rotor: Central ring assembly that rotates within the stator, transmitting torque to the filament.

C ring: Cytoplasmic switch complex composed of FliG, FliM and FliN that mediates directional switching.

Symmetry mismatch: Difference in subunit number between connected rings that modulates motor efficiency and adaptability.

Cryo-electron microscopy: Imaging technique that captures near-atomic structures of macromolecular assemblies at cryogenic temperatures.

References

1. Structural basis of the bacterial flagellar motor rotational switching. Cell Research (2024).
2. Ion selectivity and rotor coupling of the Vibrio flagellar sodium-driven stator unit. Nature Communications (2023).
3. Load-Dependent Assembly of the Bacterial Flagellar Motor. mBio (2013).
4. The flagellar motor of Vibrio alginolyticus undergoes major structural remodeling during rotational switching. eLife (2020).
5. Native flagellar MS ring is formed by 34 subunits with 23-fold and 11-fold subsymmetries. Nature Communications (2021).