Table 1.
Bacterial strains and plasmids.
Table 2.
PCR Primers.
Fig 1.
Rhamnolipids production of various B. glumae strains.
Bacteria were grown in liquid swarming medium for 24 hours at 34°C. The mutant rhlA- is not capable of producing rhamnolipids. While the production of rhamnolipids by the tofI- mutant is almost abrogated, near wild-type production level are restored upon exogenous addition of 8 μM C8-HSL. The C8-HSL addition to wild-type does not significantly modify its rhamnolipid production. The error bars indicate the standard deviation of the mean for three independent cultures.
Fig 2.
Swarming motilities of various B. glumae strains.
Plates were incubated for 18 hours at 34°C. (a) Wild-type strain BGR1. (b) rhlA- mutant which is not capable to produce rhamnolipids completely loses its swarming phenotype. (c) Swarming of quorum sensing signal negative tofI- mutant is essentially abolished. (d) Wild-type strain (right) and rhlA- mutant (left) were placed on the same plate separated by a 2 cm distance between the inoculation points. The rhlA- mutant, which is incapable of swarming by itself, recovers its swarming phenotype by using the rhamnolipids diffusing from the wild-type strain colony. (e) Swarming motility of the tofI- mutant is recovered by exogenous addition of 8 μM C8-HSL to the swarming medium. (f) The rhlA- mutant recovers its swarming following exogenous supply of rhamnolipids, applied as a 5 μl drop of a 100 mg/ml rhamnolipids methanol solution on the surface of the swarming medium prior from inoculation at a 1 cm distance. (g) The addition of rhamnolipids to the swarming medium was performed like in (f), and similarly promotes the swarming of the tofI- mutant.
Fig 3.
Expression from the rhl operon promoter in wild-type and tofI- strains carrying a chromosomal rhlA’-lux transcriptional reporter.
Cultures were performed in liquid swarming medium cultures at 34°C for 10 h. The activity of rhlA-lux is significantly lower in the tofI- mutant than the wild-type strain and increases with the addition of 8 μM C8-HSL to the culture medium. The error bars indicate the standard deviation of the mean for three independent experiments.
Fig 4.
Swarming motility of tofI- mutant at 28°C and 37°C.
(a) Wild-type strain BGR1 exhibits swarming at both temperatures, however it has larger/less defined tendrils than at 34°C. (b) No swarming of the tofI- mutant is observed at 37°C, and at 28°C it is nearly abolished, like at 34°C (Fig 2c). (c) While the tofI- mutant recovers its swarming upon exogenous addition of rhamnolipids at 28°C, the complementation is not achieved at 37°C.
Fig 5.
Swimming motility of B. glumae strains.
Motility capacity was measured by diameter of motility zone on swimming agar plates at 34°C. The error bars indicate the standard deviation of the mean for three independent experiments.