It is believed that swarming click here motility in P. mirabilis facilitates ascending colonization of the urinary tract (Allison et al., 1994). A study involving phenotypic variants of Pseudomonas fluorescens F113 also suggests a role of swarming in the colonization
of the alfalfa rhizosphere. These P. fluorescens F113 phenotypic variants demonstrated increased swimming motility and swarmed under conditions that did not allow swarming of the wild-type strain. Additionally, these variants preferentially colonized distal parts of the roots that are not easily reached by the wild type (Sánchez-Contreras et al., 2002). Swarming motility is currently not well characterized in nitrogen-fixing bacteria. The first report on surface migration
in rhizobia was on a Sinorhizobium meliloti strain with a mutation in fadD, a gene involved in fatty acid metabolism (Soto et al., 2002). Rhizobium etli has also been demonstrated to have a quorum-sensing-regulated swarming behavior (Daniels et al., 2006). Rhizobium leguminosarum bv. viciae is a symbiont of plant species belonging to the Tribe Vicieae, which includes the genera Vicia, Lathyrus, Pisum, and Lens. In this paper, we describe the optimized conditions for swarming motility in R. leguminosarum bv. viciae, the development of the swarming phenotype, the morphology of the swarmer cells, the antibiotic resistance profile, and the expression of flagellar genes under swarming conditions. CYC202 concentration The bacterial strains used in this study are listed in Table 1. Rhizobium leguminosarum strains
were grown in tryptone–yeast (TY) medium (Beringer, 1974) and were used as inoculum for the swarm assays. The basal medium used for the swarm assays contained the following: 0.01% K2HPO4; 0.01% NaCl; 0.02% MgSO4· 7H2O; 0.04% KH2PO4; 0.4% yeast extract; and 0.7% Bacto agar. The swarm medium was composed of the basal medium and a supplementary carbon source (-)-p-Bromotetramisole Oxalate (0.1% of any of the following: glycerol, mannitol, rhamnose, and erythritol). Agar plates containing 30 mL of the swarm medium were air-dried with the lid on, on the bench, for 24 h. The strains used to inoculate the swarm plates were grown in TY broth for 24 h. The cell density (OD600 nm) was adjusted to a range of 1.2–1.8. A 1.5 μL culture suspension was inoculated at the center of the swarm plate and then the plate was wrapped with parafilm. The plates were incubated at 22 °C for 3–4 weeks. The effect of temperature on swarming was determined by incubating the swarm plates at 30 and at 22 °C. Cultures with different cell densities (OD600 nm) were also used to determine the effect of inoculum size on swarming. To determine whether swarming motility is dependent on the type of carbon source present, the following sugars were supplemented to the basal swarm medium at a final concentration of 0.1%: erythritol, rhamnose, mannitol, and glycerol.