(190am) Modulation of Ultrasensitive Signaling in Bacteria By Mechanical Forces

Mechanical forces are known to influence signaling in several biological systems. In recent years, various mechanosensitive proteins have been implicated in bacterial colonization and pathogenesis. Our earlier work showed that the bacterial flagellar motor, an organelle made up of several transmembrane proteins, is an adaptive mechanosensor (Lele et al., PNAS, 2013). Recent results suggest that the mechanosensitive torque-generating units within the flagellar motor are activated through a catch-bond type mechanism (Chawla et al., Sci Rep, 2017). We have found additional mechanosensitive functions in the flagellar motor: a molecular switch, which facilitates reversals between counterclockwise (CCW) and clockwise (CW) directions of flagellar rotation, is also modulated by mechanical signals. Such modulation is likely important for chemotaxis and bacterial swarming, but the molecular mechanisms remain unknown. Here, we examined how viscous loads (mechanical forces) modulate the activity of the flagellar switch by controlling its ultrasensitive response to an allosteric response regulator, CheY-P. We employed the tethered-bead approach as well as tethered cell techniques to apply varying magnitudes of mechanical forces on individual motors. Next, we measured the switch activities in a large population of cells and determined the dose-response relations (motor activity-[CheY-P]) as a function of load following a previous approach (Lele et al., Sci Adv, 2015). Our preliminary observations suggest that modulation either occurs through the control of the flagellar switch structure or via the mechanosensitive response of stator-units involved in motor rotation. It is likely that the ultrasensitive switch behavior is modulated in the first few minutes following a mechanical stimulus, followed by adaptation to its pre-stimulus response.

Keywords: Signaling, Mechanical Force, Bacterial Motors