Intact structures of the bacterial flagella have been observed for different bacterial species by electron cryotomography and subtomogram averaging.

The combination of experimental and mathematical evidence demonstrates that a simple, injection-diffusion mechanism controls bacterial flagella growth outside the cell.

Wheels as far as I know have never evolved in, well, one possible exception which is the bacterium, the bacterial flagella.

Accordingly, bacterial flagella and T4P represent attractive targets for novel antivirulence drugs interfering with synthesis, assembly, and function of these motility structures.

Bacterial flagella contain a specialized secretion apparatus that functions to deliver the protein subunits that form the filament and other structures to outside the membrane.