Flagellated bacteria are propelled by the rotation of helical flagellar filaments, each with a flagellar motor at its base. Taking Escherichia coli (E. coli) as an example, each cell has 3–7 flagella whose rotation as a helical bundle enables the cell to move smoothly. The flagellar motors are sensitive to the load they drive, generating varied torque at different speeds. The motor torque remains approximately constant within a knee speed, while dropping rapidly above the knee speed.
