  Recent experiments on the bacterial flagellar motor have shown that the
structure of this nanomachine, which drives locomotion in a wide range of
bacterial species, is more dynamic than previously believed. Specifically, the
number of active torque-generating units (stators) was shown to vary across
applied loads. This finding invalidates the experimental evidence reporting
that limiting (zero-torque) speed is independent of the number of active
stators. Here, we propose that, contrary to previous assumptions, the maximum
speed of the motor is not universal, but rather increases as additional
torque-generators are recruited. This result arises from our assumption that
stators disengage from the motor for a significant portion of their
mechanochemical cycles at low loads. We show that this assumption is consistent
with current experimental evidence and consolidate our predictions with
arguments that a processive motor must have a high duty ratio at high loads.
