From the Wiki: > "The bacterial flagellum is driven by a rotary engine (Mot complex) made up of protein, located at the flagellum's anchor point on the inner c

From the Wiki: > "The bacterial flagellum is driven by a rotary engine (Mot complex) made up of protein, located at the flagellum's anchor point on the inner cell membrane. The engine is powered by proton motive force, i.e., by the flow of protons (hydrogen ions) across the bacterial cell membrane... The rotor transports protons across the membrane, and is turned in the process. *The rotor alone can operate at 6,000 to 17,000 rpm*[!], but with the flagellar filament attached usually only reaches 200 to 1000 rpm." Nature never ceases to amaze.