title: Controlled synthesis of the DSF cell-cell signal is required for biofilm formation and virulence in Xanthomonas campestris.
abstract: Virulence of the black rot pathogen Xanthomonas campestris pv. campestris (Xcc) is regulated by cell-cell signalling involving the diffusible signal factor DSF. Synthesis and perception of DSF require products of genes within the rpf cluster (for regulation of pathogenicity factors). RpfF directs DSF synthesis whereas RpfC and RpfG are involved in DSF perception. Here we have examined the role of the rpf/DSF system in biofilm formation in minimal medium using confocal laser-scanning microscopy of GFP-labelled bacteria. Wild-type Xcc formed microcolonies that developed into a structured biofilm. In contrast, an rpfF mutant (DSF-minus) and an rpfC mutant (DSF overproducer) formed only unstructured arrangements of bacteria. A gumB mutant, defective in xanthan biosynthesis, was also unable to develop the typical wild-type biofilm. Mixed cultures of gumB and rpfF mutants formed a typical biofilm in vitro. In contrast, in mixed cultures the rpfC mutant prevented the formation of the structured biofilm by the wild-type and did not restore wild-type biofilm phenotypes to gumB or rpfF mutants. These effects on structured biofilm formation were correlated with growth and disease development by Xcc strains in Nicotiana benthamiana leaves. These findings suggest that DSF signalling is finely balanced during both biofilm formation and virulence.
authors.affiliation: Fundación Pablo Cassará, Centro de Ciencia y Tecnología Dr César Milstein and Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Saladillo 2468 C1440FFX, Ciudad de Buenos Aires, Argentina.
authors.forename: Pablo S
authors.initials: PS
authors.lastname: Torres
authors.forename: Florencia
authors.initials: F
authors.lastname: Malamud
authors.forename: Luciano A
authors.initials: LA
authors.lastname: Rigano
authors.forename: Daniela M
authors.initials: DM
authors.lastname: Russo
authors.forename: María Rosa
authors.initials: MR
authors.lastname: Marano
authors.forename: Atilio P
authors.initials: AP
authors.lastname: Castagnaro
authors.forename: Angeles
authors.initials: A
authors.lastname: Zorreguieta
authors.forename: Kamal
authors.initials: K
authors.lastname: Bouarab
authors.forename: John Maxwell
authors.initials: JM
authors.lastname: Dow
authors.forename: Adrián A
authors.initials: AA
authors.lastname: Vojnov
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D018441:Biofilms / Q000254:growth & development; D018613:Microscopy, Confocal; D009154:Mutation; D010935:Plant Diseases / Q000382:microbiology*; D018515:Plant Leaves / Q000382:microbiology; D053038:Quorum Sensing; D014026:Nicotiana / Q000382:microbiology*; D014774:Virulence; D016959:Xanthomonas campestris / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins