The bacterial flagellar motor and its structural diversity

•The rotor and stator of the flagellar motor are highly-dynamic structures.•The export components show dynamic interactions with their binding partners.•The assembly mechanism of the core structure of the motor is conserved.•There is structural diversity in the motor across bacterial species.

The bacterial flagellum is a reversible rotary motor powered by an electrochemical-potential difference of specific ions across the cytoplasmic membrane. The H+-driven motor of Salmonella spins at ∼300 Hz, whereas the Na+-driven motor of marine Vibrio spp. can rotate much faster, up to 1700 Hz. A highly conserved motor structure consists of the MS ring, C ring, rod, and export apparatus. The C ring and the export apparatus show dynamic properties for exerting their functional activities. Various additional structures surrounding the conserved motor structure are observed in different bacterial species. In this review we summarize our current understanding of the structure, function, and assembly of the flagellar motor in Salmonella and marine Vibrio.