(460a) Motility, Surface-Sensing and Signaling in Bacteria

Surface-colonization by bacteria is often the first step towards bacterial community-development. For colonization to occur, cells must approach a surface and detect its presence. The molecular mechanisms of surface-detection are unknown but there is consensus that surface-dependent mechanical signals likely trigger gene-expression and biochemical signaling that promote colonization. Due to incessant Brownian motion, cells continually experience mechanical forces even when they are far from surfaces. In order to prevent premature turning-on of mechanosensitive genes, cells must be able to discriminate between mechanical forces that arise in the bulk fluid and those that emerge near a surface. I will discuss how motile cells likely make this distinction by measuring surface-induced increase in drag, and in particular how extracellular appendages assist in this purpose. Our measurements highlighting the role of the flagella (otherwise known to be involved in motility) in sensing of surfaces will be presented. A few sensors such as the flagellum likely aid in circumventing the need for a high concentration of sensors all over the cell body, while at the same time providing high sensitivities to mechanical inputs. I will discuss data that explain how this is likely achieved via the regulation of the sensitivities of actuating protein complexes to the outputs of the sensor modules in a standard two-component signaling pathway. Results further indicate that mutations that inhibit such sensitivities disrupt certain motile phenotypes, such as swarming, which enables bacterial colonies to cover large surfaces and possibly invade host tissues. This suggests an indirect link between the intracellular events and the external hydrodynamic drag. I will then conclude with a brief note on new results that show how similar mechanically-stimulated regulatory events influence a host of important processes such as bacterial competence, which regulates the uptake of extracellular DNA.