Biofilms, flagella, and mechanosensing of surfaces by bacteria

•Bacterial flagella serve as mechanosensors responding to surface contact. •Flagellar stators (MotAB) play a critical role in flagellum-mediated surface-sensing. •Perturbation of proton motive force or ion flow through the stators appears to be important in response to a surface. •One of the major outcomes of flagellar mechanosensing is control of the flagellar master regulator. Formation of a bacterial biofilm is a developmental process that begins when a cell attaches to a surface, but how does a bacterial cell know it is on or near a surface in the first place? The phase of this ‘swim-or-stick’ switch is determined by a sensory transduction mechanism referred to as surface sensing, which involves the rotating bacterial flagellum. This review explores six bacterial species as models of flagellar mechanosensing of surfaces to understand the current state of our knowledge and the challenges that lie ahead. A common link between these bacteria is a requirement for the proper function of the flagellar motor stators that channel ions into the cell to drive flagellar rotation. Conditions that affect ion flow act as a signal that, ultimately, controls the master transcriptional regulatory circuits controlling the flagellar hierarchy and biofilm formation. Formation of a bacterial biofilm is a developmental process that begins when a cell attaches to a surface, but how does a bacterial cell know it is on or near a surface in the first place? The phase of this ‘swim-or-stick’ switch is determined by a sensory transduction mechanism referred to as surface sensing, which involves the rotating bacterial flagellum. This review explores six bacterial species as models of flagellar mechanosensing of surfaces to understand the current state of our knowledge and the challenges that lie ahead. A common link between these bacteria is a requirement for the proper function of the flagellar motor stators that channel ions into the cell to drive flagellar rotation. Conditions that affect ion flow act as a signal that, ultimately, controls the master transcriptional regulatory circuits controlling the flagellar hierarchy and biofilm formation. a secondary messenger used by many bacteria to regulate biofilm formation. High levels of c-di-GMP promote biofilms, whereas low levels of c-di-GMP promote motility. protein subunit that comprises the flagellar filament. flagella that are used for swarming, and that are distributed around the surface of the cell in some bacteria that also possess polar flagella. Lateral and polar flagella are encoded by different sets of genes. an organelle, a biological complex, or individual protein that detects and responds to physical forces exerted by the local environment and transduces this signal to control the transcriptional machinery. the potential (electrical charge) across a bacterial membrane relative to the fluid outside of the concentration of potassium, sodium, chloride, and other diffusible ions. ΔΨ is one component of proton motive force. (The second is ΔpH.) flagella used for swimming, and localized to one or both ends of a rod-shaped bacterium. energy that is generated by the transfer of protons across a membrane that can be used for a variety of purposes, including synthesizing ATP. It is composed of the difference in proton concentration (ΔpH) and the electrical charge (ΔΨ) across a membrane. is a bacterial flagella-dependent motile behavior that allows cells to move over surfaces in a coordinated manner and expand the population to new locations. The process of swarming is distinct from swimming in that swarming is a multicellular process that occurs on solid surfaces or in viscous liquids, and requires differentiation of a vegetative swimmer cell into a specialized cell type called a swarmer cell. morphological change of some bacteria from a planktonic or vegetative form that moves by swimming in liquid medium to a form in which the cells move across solid surfaces. Swarmer cell differentiation results in an increased number of flagella per cell and, in some bacteria, an alteration in how the flagella are distributed around the cell surface, as well as a significant elongation of the swarmer cells due to an inhibition of septation. in its simplest form, composed of a membrane-bound sensor histidine kinase protein that senses specific environmental stimuli and its cognate response regulator protein that mediates the response, frequently through direct binding to DNA and subsequent differential expression of target gene transcription.