A cell density-dependent lag period was observed before swarming motility was MI-503 order initiated. Surface migration began 3–5 days after inoculation and a full swarming phenotype was observed 3 weeks after inoculation. The swarming front was

preceded by a clear extracellular matrix, from which we failed to detect surfactants. The edge of the swarming front formed by VF39SM was characterized by hyperflagellated cells arranged in rafts, whereas the cells at the point of inoculation were indistinguishable from vegetative cells. Swarmer cells formed by 3841, in contrast, showed a minor increase in flagellation, with each swarmer cell exhibiting an average of three flagellar filaments, compared with an average of two flagella per vegetative cell. Reflective of their hyperflagellation, the VF39SM swarmer cells GSK-3 beta pathway demonstrated an increased expression

of flagellar genes. VF39SM swarmed better than 3841 under all the conditions tested, and the additional flagellation in VF39SM swarm cells may contribute to this difference. Metabolism of the supplemented carbon source appeared to be necessary for surface migration as strains incapable of utilizing the carbon source failed to swarm. We also observed that swarmer cells have increased resistance to several antibiotics. Swarming motility refers to the coordinated movement of groups of bacterial cells on semi-solid surfaces (Fraser & Hughes, 1999; Braeken et al., 2008; Verstraeten et al., 2008), and often involves the differentiation of vegetative cells into hyperflagellated swarmer cells (Fraser & Hughes, 1999). The differentiated swarmer cells are organized parallel to their long axis in the form of rafts that rapidly colonize the entire surface of an agar medium (Harshey, 1994; Daniels et al., 2004). The rapid outward migration of the swarmer cells at the edge of the swarming colonies is accompanied by bacterial growth inside the colony (Sharma & Anand, 2003). The swarm front is preceded by a clear layer of slime-like extracellular material that also confers a glistening effect on

the swarming colonies (Harshey, 1994; Fraser & Hughes, 1999; Daniels et al., 2004; Julkowska et al., 2004). Quisqualic acid This extracellular matrix, which serves as a hydrated environment for the swarmer cells, consists of polysaccharides, biosurfactants, peptides, and proteins (Verstraeten et al., 2008). Swarming has been well studied in Proteus mirabilis, Proteus vulgaris, and in some species of Bacillus and Clostridium (Sharma & Anand, 2003). At present, swarming has been demonstrated in a wide range of bacteria including members of Vibrio, Serratia, Chromobacterium, Escherichia, Salmonella, Azospirillum, Pseudomonas, Yersinia, Sinorhizobium, Rhizobium, and Agrobacterium (Hall & Krieg, 1983; Harshey & Matsuyama, 1994; Kohler et al., 2000; Soto et al., 2002; Sharma & Anand, 2003; Kim & Surette, 2005; Daniels et al., 2006; Sule et al., 2009).