Award for Outstanding Doctoral Thesis Research in Biological Physics Talk: Mechanics and energetics of the bacterial flagellar motor

The bacterial flagellar motor (BFM) is an ion-powered nanomachine that drives swimming in many bacteria. This protein complex is comprised of several transmembrane rings connected to a long flagellar filament by a flexible hook. Rotation is known to occur via an interaction between one or more membrane-embedded “stator” units, and protein spokes on the periphery of the spinning “rotor” ring. In this talk, I will touch on three features of the motor: (1) its fundamental mechanochemical cycle, (2) the dynamic remodelling of motor structure in response to its environment, and (3) the efficiency of the motor. First, taking into account all the structural and dynamic biophysical experimental evidence to date, we present a mechanically-specific, testable model of the motor’s mechanism of torque generation. We validate this theoretical model of the BFM’s mechanochemical cycle against experiments done on motors with a single stator. Second, we extend this base model to consider the behavior of multi-stator motors. Stator units have been shown to dynamically bind and leave the motor. We present several recent experiments that shine light on the nature of this complex process, which is influenced by several factors, including the ion gradient, external load, and motor speed. Finally, we also discuss experiments directly measuring the relationship between ion flux through the membrane and motor speed, towards answering the question of whether the motor is loosely or tightly coupled to ion flux — that is, whether each ion passage constitutes a fully efficient power stroke.