title: Phosphorus limitation enhances biofilm formation of the plant pathogen Agrobacterium tumefaciens through the PhoR-PhoB regulatory system.
abstract: The plant pathogen Agrobacterium tumefaciens forms architecturally complex biofilms on inert surfaces. Adherence of A. tumefaciens C58 was significantly enhanced under phosphate limitation compared to phosphate-replete conditions, despite slower overall growth under low-phosphate conditions. Replacement of Pi with sn-glycerol-3-phosphate and 2-aminoethylphosphonate yielded similar results. The increase in surface interactions under phosphate limitation was observed in both static culture and continuous-culture flow cells. Statistical analysis of confocal micrographs obtained from the flow cell biofilms revealed that phosphate limitation increased both the overall attached biomass and the surface coverage, whereas the maximum thickness of the biofilm was not affected. Functions encoded on the two large plasmids of A. tumefaciens C58, pTiC58 and pAtC58, were not required for the observed phosphate effect. The phosphate concentration at which increased attachment was observed triggered the phosphate limitation response, controlled in many bacteria by the two-component regulatory system PhoR-PhoB. The A. tumefaciens phoB and phoR orthologues could only be disrupted in the presence of plasmid-borne copies of the genes, suggesting that this regulatory system might be essential. Expression of the A. tumefaciens phoB gene from a tightly regulated inducible promoter, however, correlated with the amount of biofilm under both phosphate-limiting and nonlimiting conditions, demonstrating that components of the Pho regulon influence A. tumefaciens surface interactions.
authors.affiliation: Department of Biology, 1001 E. 3rd St., Jordan Hall 142, Indiana University, Bloomington, IN 47405-1847, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Danhorn
authors.forename: Morten
authors.initials: M
authors.lastname: Hentzer
authors.forename: Michael
authors.initials: M
authors.lastname: Givskov
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Parsek
authors.forename: Clay
authors.initials: C
authors.lastname: Fuqua
mesh_terms: D016960:Agrobacterium tumefaciens / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D000615:Aminoethylphosphonic Acid / Q000378:metabolism; D001422:Bacterial Adhesion / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D018441:Biofilms / Q000254:growth & development*; D018533:Biomass; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D020043:Genes, Essential; D005816:Genetic Complementation Test; D005994:Glycerophosphates / Q000378:metabolism; D018613:Microscopy, Confocal; D016254:Mutagenesis, Insertional; D009154:Mutation; D010758:Phosphorus / Q000378:metabolism*; D010957:Plasmids; D015398:Signal Transduction / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D005994:Glycerophosphates; C061278:PhoB protein, Bacteria; C061279:PhoR protein, Bacteria; D010758:Phosphorus; D000615:Aminoethylphosphonic Acid