Swarming of Pseudomonas aeruginosa Is Dependent on Cell-to-Cell Signaling and Requires Flagella and Pili

Abstract

We describe swarming in Pseudomonas aeruginosa as a third mode of surface translocation in addition to the previously described swimming and twitching motilities. Swarming in P. aeruginosa is induced on semisolid surfaces (0.5 to 0.7% agar) under conditions of nitrogen limitation and in response to certain amino acids. Glutamate, aspartate, histidine, or proline, when provided as the sole source of nitrogen, induced swarming, while arginine, asparagine, and glutamine, among other amino acids, did not sustain swarming. Cells from the edge of the swarm were about twice as long as cells from the swarm center. In both instances, bacteria possessing two polar flagella were observed by light and electron microscopy. While a fliC mutant of P. aeruginosa displayed slightly diminished swarming, a pilR and a pilA mutant, both deficient in type IV pili, were unable to swarm. Furthermore, cells with mutations in the las cell-to-cell signaling system showed diminished swarming behavior, while rhl mutants were completely unable to swarm. Evidence is presented for rhamnolipids being the actual surfactant involved in swarming motility, which explains the involvement of the cell-to-cell signaling circuitry of P. aeruginosa in this type of surface motility.Pseudomonas aeruginosa is a gram-negative bacterium living in soil and aqueous environments, where it survives due to its extraordinary metabolic abilities. P. aeruginosa is also a typical opportunistic pathogen which colonizes the lungs of cystic fibrosis patients and causes severe infections in immunocompromised hosts. Due to its notorious elevated intrinsic resistance to antimicrobial agents and its ability to attach to and to form biofilms on medical devices (9), P. aeruginosa is difficult to eradicate in the hospital environment.P. aeruginosa has a single polar flagellum which enables the cell to swim in aqueous environments and in low-agar (Ͻ0.4%) medium. The flagellum and the chemotaxis system, consisting of chemoreceptors (11, 49) and a signal relay system similar to that of Escherichia coli (25,31), allow the bacterium to respond to attractants and repellents. In addition, P. aeruginosa is able to propagate at surface interfaces by twitching motility, which is mediated by type IV pili (5,12,53). Twitching motility is believed to result from the extension and retraction of the pilus filament, which propels the cells across a surface. Pilus synthesis and assembly require at least 40 genes which are located in several unlinked regions on the chromosome (22). The nature of the environmental signal that triggers the expression of pili is not known. Pili are important for attachment to epithelial cells (8, 17) and contribute to the virulence of P. aeruginosa in animal models (19,50,51). Furthermore, twitching motility and, hence, type IV pili are required for the formation of biofilms on abiotic surfaces (38).Besides swimming and twitching, several gram-negative bacteria are able to propagate on semisolid surfaces (i.e., 0.4 to 1.0% agar) in a coordinated manner by swarming ...

Branched swarming patterns on a synthetic medium formed by wild-type Bacillus subtilis strain 3610: detection of different cellular morphologies and constellations of cells as the complex architecture develops

“…As expected with the cells growing more slowly on glycerol, swarming was slower but the final results were essentially the same (data not shown). This is in contrast to swarming in E. coli (Harshey & Matsuyama, 1994) or Pseudomonas aeruginosa (Kohler et al, 2000), which is abolished by growth on glycerol. In the presence or absence of tryptophan or lysine, the swarming rate and patterns obtained were indistinguishable.…”

The Pseudomonas aeruginosa oxidative stress regulator OxyR influences production of pyocyanin and rhamnolipids: protective role of pyocyanin

“…Swarming is dependent on the combination of the polar flagellum, type IV pili and rhamnolipid production (Caiazza et al, 2005;Kohler et al, 2000). This type of motility is almost completely absent in the oxyR mutant grown on CAA medium (Fig.…”

A Homologue of the 3-Oxoacyl-(Acyl Carrier Protein) Synthase III Gene Located in the Glycosylation Island of Pseudomonas syringae pv. tabaci Regulates Virulence Factors via N -Acyl Homoserine Lactone and Fatty Acid Synthesis

“…Previously, it was reported that swarming motility is enhanced by the addition of biosurfactants and that mutants of Serratia liquefaciens defective in biosurfactant production have no swarming ability (19,21). Indeed, swarming motility in the ⌬orf3 mutant was enhanced in both SWM and MMMF plates with 0.5% agar (Fig.…”