  The bacterial flagellar motor is an ion-powered transmembrane protein complex
which drives swimming in many bacterial species. The motor consists of a
cytoplasmic 'rotor' ring and a number of 'stator' units, which are bound to the
cell wall of the bacterium. Recently, it has been shown that the number of
functional torque-generating stator units in the motor depends on the external
load, and suggested that mechanosensing in the flagellar motor is driven via a
'catch bond' mechanism in the motor's stator units. We present a method that
allows us to measure -- on a single motor -- stator unit dynamics across a
large range of external loads, including near the zero-torque limit. By
attaching superparamagnetic beads to the flagellar hook, we can control the
motor's speed via a rotating magnetic field. We manipulate the motor to four
different speed levels in two different ion-motive force (IMF) conditions. This
framework allows for a deeper exploration into the mechanism behind
load-dependent remodelling by separating out motor properties, such as rotation
speed and energy availability in the form of IMF, that affect the motor torque.
