(584s) Dynamics of Mechanosensing in the Bacterial Flagellar Motor | AIChE

(584s) Dynamics of Mechanosensing in the Bacterial Flagellar Motor


Lele, P. - Presenter, Texas A&M Engineering Experiment Station
Berg, H. C., Harvard University
Hosu, B., Harvard University

Mechanosensing by the flagellum is thought to trigger bacterial swarmer-cell differentiation, an important step in pathogenesis. How the flagellar motor senses mechanical stimuli is not known. To study this problem, we suddenly increased the viscous drag on single motors, by using optical tweezers to attach latex beads to the flagellum. From the initial speed (after the load change), we inferred that motors running at very low loads are driven by 1 or at most 2 force-generating units. Following the load change, motors gradually adapted by increasing their speeds in a stepwise manner (over a period of a few minutes). Single-motor TIRF imaging of YFP-MotB (part of a stator force-generating unit) confirmed that the response to sudden increments in load occurred by the addition of new force-generating units.  We estimate that 6-11 force-generating units drive motors at high loads.  Wild-type motors and motors locked in the CW or CCW state behaved in a similar manner, as did motors in cells deleted for fliL or for genes in the chemotaxis signaling pathway.  Thus it appears that stators themselves act as dynamic mechanosensors. This is a rare example of a biological motor employing a variable number of force generating units to tailor its response to varying external viscous loads.