A mechanical signal transmitted by the flagellum controls signalling in Bacillus subtilis

Abstract

In the natural environment bacteria predominantly live adhered to a surface as part of a biofilm. While many of the components needed for biofilm assembly are known, the mechanism by which microbes sense and respond to contact with a surface is poorly understood. Bacillus subtilis is a Gram-positive model for biofilm formation. The DegS–DegU two-component system controls several multicellular behaviours in B. subtilis, including biofilm formation. Here we identify the B. subtilis flagellum as a mechanosensor that activates the DegS–DegU regulatory pathway. Inhibition of flagellar rotation by deletion or mutation of the flagellar stator gene, motB, results in an increase in both degU transcription and DegU∼P driven processes, namely exoprotease production and poly-γ-dl-glutamic acid biosynthesis. Similarly, inhibition of flagellar rotation by engaging the flagellar clutch or by tethering the flagella with antibodies also promotes an increase in degU transcription that is reflective of increased DegU∼P levels in the cell. Collectively, these findings strongly indicate that inhibition of flagellar rotation acts as a mechanical trigger to activate the DegS–DegU two-component signal transduction system. We postulate that inhibition of flagellar rotation could function as a mechanical trigger to activate bacterial signal transduction cascades in many motile bacteria upon contact with a surface.

Loss of FliL Alters Proteus mirabilis Surface Sensing and Temperature-Dependent Swarming

“…Many studies emphasize a role of the flagellum in mechanosensing of surfaces (2,8,64,65), and the present results demonstrate the importance of FliL in the surface-sensing sensory transduction pathway. To summarize our present results, the data reveal that loss of FliL alters the sensitivity of P. mirabilis cells to viscosity by lowering the low-viscosity threshold of the surfacesensing response without affecting the cell's high-viscosity response.…”

Adaptor-mediated Lon proteolysis restrictsBacillus subtilishyperflagellation

“…Surface sensing is poorly understood but seems to integrate information from cell surface appendages such as the adhesion of pili or the impedance of flagellar rotation (28,30,40,42,43). Transduction of the surface signal is also poorly understood and the signal transduction components that have been discovered may be species specific (34,43,45,46). In B. subtilis, the mechanism of surface recognition is unknown, but here we demonstrate that signal transduction is mediated by Lon-dependent proteolysis of a master regulator and the physiological output is an increase in flagellar density.…”

The Matrix Reloaded: How Sensing the Extracellular Matrix Synchronizes Bacterial Communities

“…The same phenotype was achieved by other methods that hampered flagellar rotation, such as (i) mutations in MotB that disrupted proton flux through the motor, (ii) addition of specific antibodies against the flagellar filament, and (iii) overexpression of EpsE, which can function as a molecular clutch that separates the flagellar stator and rotor compartments (155,156). Overproduction of ␥-PGA required the presence of DegU and DegS (150), as well as of proteins involved in flagellar filament assembly (151). The results of the studies presented here suggest that hampering the rotation of the flagella during initial attachment results in altered gene expression.…”

“…B. subtilis biofilm development requires the activation of three transcriptional regulators: ComA, Spo0A, and DegU (38). Recent studies showed that the disruption of flagellar rotation increased the DegUϳP level (150,151). Phosphorylated DegU triggers the biosynthesis of ␥-polyglutamic acid (␥-PGA), a unique ECM polymer composed of glutamic acid and produced by the pgs operon (152)(153)(154).…”

“…Psl in P. aeruginosa, and the B. subtilis exopolysaccharide, are specifically sensed by each of these bacteria and are used as a signal to increase ECM production, demonstrating a positive-feedback loop (114,148). Another example is B. subtilis, which uses its flagella as mechanosensory organelles that might sense the ECM viscous environment; halting the flagellum leads to the induction of ECM production (150,151).…”