Type IV pili mechanochemically regulate virulence factors in Pseudomonas aeruginosa

Abstract

Bacteria have evolved a wide range of sensing systems to appropriately respond to environmental signals. Here we demonstrate that the opportunistic pathogen Pseudomonas aeruginosa detects contact with surfaces on short timescales using the mechanical activity of its type IV pili, a major surface adhesin. This signal transduction mechanism requires attachment of type IV pili to a solid surface, followed by pilus retraction and signal transduction through the Chp chemosensory system, a chemotaxis-like sensory system that regulates cAMP production and transcription of hundreds of genes, including key virulence factors. Like other chemotaxis pathways, pili-mediated surface sensing results in a transient response amplified by a positive feedback that increases type IV pili activity, thereby promoting long-term surface attachment that can stimulate additional virulence and biofilm-inducing pathways. The methyl-accepting chemotaxis protein-like chemosensor PilJ directly interacts with the major pilin subunit PilA. Our results thus support a mechanochemical model where a chemosensory system measures the mechanically induced conformational changes in stretched type IV pili. These findings demonstrate that P. aeruginosa not only uses type IV pili for surface-specific twitching motility, but also as a sensor regulating surface-induced gene expression and pathogenicity.surface sensing | mechanotransduction | type IV pili | virulence N umerous bacterial species exhibit a range of behaviors that are specific to life on surfaces. For many pathogens, surfacespecific phenotypes are often associated with virulent activity, because many infection strategies require contact with a host (1). For example, in Pseudomonas aeruginosa, the type III secretion system, which infects by injecting toxins, requires attachment of individual cells to host-cell membranes (2). The genetic pathways that regulate P. aeruginosa secretion systems have been well characterized (3), but the environmental signals that activate these pathways remain poorly defined (4). Given the requirement for host-cell contact for efficient infection, P. aeruginosa could leverage surface contact as a signal to properly activate and coordinate pathogenicity. Indeed, our laboratory recently demonstrated that prolonged association with a solid surface contributes to P. aeruginosa pathogenicity when bacteria and host cells are forced together (5). Here we address the fundamental question of how bacteria rapidly sense surface contact and transduce this input into a cellular response over short timescales.Surface-specific behaviors require intimate contact between cells and substrate. In P. aeruginosa, contact is mediated by several adhesins, particularly type IV pili (TFP). TFP are long, motorized fimbriae that also provide cells with surface-specific twitching motility and are essential to virulence and biofilm formation (6, 7). Successive TFP extension, attachment, and retraction promote intimate association with surfaces and motility along them. Because TFP dynamically int...

Asymmetric distribution of type IV pili triggered by directional light in unicellular cyanobacteria

“…We also visualized the retraction of T4P by tracking a fluorescent bead that attached to the edge of a single pilus. This assay could contribute to quantification of the dynamic properties of T4P, which may be common in other bacteria such as Neisseria gonorrheae (6,32) or Pseudomonas aeruginosa (33). The combination of our experimental system and mutants that lack other receptors or key proteins in various species will reveal more detailed mechanisms in the near future.…”

Phosphoryl Group Flow within the Pseudomonas aeruginosa Pil-Chp Chemosensory System

“…In addition to regulating twitching motility, the P. aeruginosa Pil-Chp chemosensory system also regulates intracellular levels of cAMP (21), a second messenger that activates Vfr, a master transcriptional regulator of genes involved in P. aeruginosa pathogenesis (22). The relationship between Pil-Chp regulation of cAMP levels and twitching motility has yet to be fully elucidated (21,23); however, it has been recently proposed that Pil-Chp regulation of twitching motility and cAMP synthesis is linked to mechanical tension resulting from surface attachment of T4P (24).…”

Role of Cyclic Di-GMP and Exopolysaccharide in Type IV Pilus Dynamics

“…For Pseudomonas aeruginosa, a role for T4P as surface sensors is emerging (2); in particular, active T4P retraction has been proposed to be required (3,4). It is currently unclear, however, how T4P dynamics affect the earliest stages of biofilm formation.…”