Modulation of Ultrasensitive Signaling in Bacteria by Viscous Load on Flagellar Motor
Jyot Antani (1), Pushkar Lele (1)
1. Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, TX 77843, USA.
Mechanical forces are known to influence signaling in several biological systems. In recent years, several mechanosensitive proteins have been implicated in bacterial colonization and pathogenesis. Our earlier work showed that the bacterial flagellum, an appendage that enables motility, is an adaptive mechanosensor (Lele et al., PNAS, 2013). Recent results from our lab suggest that the mechanosensitive force-generators within the flagellar motor are activated through a catch-bond type mechanism (Chawla et al., Sci Rep, 2017). We have found additional mechanosensitive functions of the flagellar motor: a molecular flagellar switch, which enables reversals between clockwise (CW) and counterclockwise (CCW) directions of rotation, is also modulated by mechanical signals. This modulation is likely important for chemotaxis and bacterial swarming (Lele et al., Sci Adv, 2016), but the molecular mechanisms remain unknown. Here, we determined 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 popular tethered-bead assays as well as tethered cell techniques to apply varying magnitudes of viscous loads on individual motors. Next, we measured the switch activities in a large population of cells and employed a statistical distribution technique to determine the dose-response relations (CWbias-[CheY-P]) as a function of load. 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.
Keywords: Mechanosensing, clockwise bias, CheY, Eschericia coli