Characterization of swarming motility in Rhizobium leguminosarum bv. viciae

Abstract

We have characterized swarming motility in Rhizobium leguminosarum strains 3841 and VF39SM. Swarming was dependent on growth on energy-rich media, and both agar concentration and incubation temperature were critical parameters for surface migration. A cell density-dependent lag period was observed before swarming motility was 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 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.

Regulation of flagellar, motility and chemotaxis genes in Rhizobium leguminosarum by the VisN/R-Rem cascade

“…The roles of these regulators in the expression of flagellar and chemotaxis genes in R. leguminosarum were determined by cloning the orthologous genes from the sequenced strain 3841 and our laboratory strain VF39SM. We used both strains because these strains exhibit differences in the pattern of flagellation (Tambalo et al, 2010) and also in swarming motility (Tambalo et al, 2010). Strain VF39SM is peritrichously flagellated, while 3841 has one to two subpolar flagella.…”

“…We performed the studies using strains 3841 and VF39SM because the two strains exhibit substantial differences in pattern of flagellation and swarming motility (Tambalo et al, 2010). Using transcriptional fusions to a large number of genes involved in chemotaxis and motility, we demonstrate that only a subset of these genes is regulated by the VisN/R cascade.…”

Legume seed exudates and Physcomitrella patens extracts influence swarming behavior in Rhizobium leguminosarum

“…viciae VF39SM (Priefer 1989) and a R. leguminosarum VF39SM strain containing a flagellin A (flaA)-gusA transcriptional fusion (Tambalo et al 2010b). The strains were routinely grown in TY (tryptoneyeast extract) broth (Beringer 1974) or swarm medium (Tambalo et al 2010c) using the following antibiotic concentrations: streptomycin, 500 g·mL −1 ; and tetracycline, 5 g·mL −1 . The basal swarm medium contained the following: 0.01% K 2 HPO 4 , 0.01% NaCl, 0.02% MgSO 4 ·7H 2 O, 0.04% KH 2 PO 4 , 0.4% yeast extract, 0.2% glycerol, and 0.7% Difco Bacto agar.…”

“…Swarming in R. leguminosarum (Tambalo et al 2010c) and the closely related species Rhizobium etli (Daniels et al 2006) have recently been reported and partially characterized. In R. leguminosarum bv.…”

“…In R. leguminosarum bv. viciae, swarming was characterized in the closely related strains VF39SM and 3841 (Tambalo et al 2010c). The swarmer cells were shown to be hyperflagellated and had increased resistance to antibiotics relative to vegetative cells; however, specific genetic determinants and regulation of swarming behavior in R. leguminosarum bv.…”