Mechanosensing of shear by Pseudomonas aeruginosa leads to increased levels of the cyclic-di-GMP signal initiating biofilm development

Abstract

Biofilms are communities of sessile microbes that are phenotypically distinct from their genetically identical, free-swimming counterparts. Biofilms initiate when bacteria attach to a solid surface. Attachment triggers intracellular signaling to change gene expression from the planktonic to the biofilm phenotype. For , it has long been known that intracellular levels of the signal cyclic-di-GMP increase upon surface adhesion and that this is required to begin biofilm development. However, what cue is sensed to notify bacteria that they are attached to the surface has not been known. Here, we show that mechanical shear acts as a cue for surface adhesion and activates cyclic-di-GMP signaling. The magnitude of the shear force, and thereby the corresponding activation of cyclic-di-GMP signaling, can be adjusted both by varying the strength of the adhesion that binds bacteria to the surface and by varying the rate of fluid flow over surface-bound bacteria. We show that the envelope protein PilY1 and functional type IV pili are required mechanosensory elements. An analytic model that accounts for the feedback between mechanosensors, cyclic-di-GMP signaling, and production of adhesive polysaccharides describes our data well.

Clustering of bacteria with heterogeneous motility

“…The model is built at the particle scale and its parameters stand for unknown processes at a molecular scale. While it is clear that the type IV pili play a key role in bacterial adhesion [29][30][31][32], their complex interactions with surfaces and with other bacteria deserve to be studied extensively with, for example, mutant of variable number of pili or surfaces of controlled structure. The description proposed here does not, however, rely upon explicit cell-substrate or cell-cell adhesion mechanisms.…”

Mechanical stress compromises multicomponent efflux complexes in bacteria

“…Much less is known about the importance of mechanical forces to prokaryotic organisms. Bacteria have long been known to respond to mechanical stresses associated with changes in osmotic pressure and hydrostatic pressure, but recent findings indicate that mechanical stresses caused during locomotion 3 , surface adhesion 4,5 , and cell division 2 also regulate bacterial physiology.…”

“… Physical forces have long been recognized for their effects on the growth, morphology, locomotion, and survival of eukaryotic organisms 1 . Recently, mechanical forces have been shown to regulate processes in bacteria, including cell division 2 , motility 3 , virulence 4 , biofilm initiation 5,6 , and cell shape 7,8 , although it remains unclear how mechanical forces in the cell envelope lead to changes in molecular processes. In Gram-negative bacteria, multicomponent protein complexes that form rigid links across the cell envelope directly experience physical forces and mechanical stresses applied to the cell.…”

Assaying how the success of phagocytosis depends on the mechanics of a large viscoelastic target

“…Timelapse videos were obtained using an inverted phase contrast microscope with 60X objective (both from Olympus), QImaging Exi Blue CCD camera, and QCapture Pro 6 software. As described in our previous work, the stage region of this microscope is enclosed in an incubator chamber 45,48,49 . During image acquisition the microscope stage incubator was set to 37 °C, which is human body temperature.…”