In staining experiments, we found no evidence for a hyperflagellated swarmer cell. This is similar to reports using P. aeruginosa in swarming studies, where the cell morphology was elongated, but polar localization of the flagella was maintained [22]. The production of the wetting agent is inhibited when the bacteria are incubated in a humidified chamber (Fig 3), and the swarming rate is reduced under those

conditions (Fig 2). This indicates that the wetting agent is critical for a full swarming response. Some motility is observed in the cultures with inhibitory levels of CR present, which may be consistent with an alternative motility such as sliding motility [18]. The observed branching pattern on plates learn more incubated in a humidified chamber with inhibitory see more concentrations of CR is consistent with an alternative mode of surface movement, driven by increase production of hydrophilic exopolysaccharide, or alternatively by the matrix absorbing water from the air, and thereby increasing the spread of the colony. The observed edge is consistent with increased

colony water content, and the absence of a wetting agent to decrease the surface tension of the agar. Further investigation of this possibility is necessary. Although surfactants such as rhamnolipid [39], serrawettin [42], and surfactin [15] have been identified as critical components of swarming, in at least one case there is evidence that the wetting agent is not a surfactant [43]. We are currently in the process of isolating and identifying the V. paradoxus EPS wetting agent using biochemical and genetic means. The swarms display the

polarity observed in many species, with repellent signals inhibiting the merging of adjacent swarms (Fig 7G). Under certain nutrient conditions, such as use of CAA as sole C and N source, swarms merge readily (not shown). A similar response was seen when tryptophan was used as sole N source, suggesting that this amino acid is involved in the phenotype. An explanation for this response may be related to the production of exopolysaccharides (eps), which may be responsible for the fluid flow in the expanding swarm. The force that drives swarm expansion may be generated by flagellar activity as well as the accumulation of a hydrophilic Amobarbital eps that flows out from the dense center of the swarm. Increased formation of eps may result in “”overflow”" of the swarm, where the edge cannot stop fast enough to prevent the mixing of adjacent swarms. Alternatively, the wetting agent composition may be altered under certain conditions, leading to the observed changes in motility and swarm structure. Recent work has supported the idea that swarms respond to repellent signals based on the detection of specific signals encoded in the ids gene cluster in Proteus mirabilis [44].