title: Agrobacterium tumefaciens ExoR represses succinoglycan biosynthesis and is required for biofilm formation and motility.
abstract: The ubiquitous plant pathogen Agrobacterium tumefaciens attaches efficiently to plant tissues and abiotic surfaces and can form complex biofilms. A genetic screen for mutants unable to form biofilms on PVC identified disruptions in a homologue of the exoR gene. ExoR is a predicted periplasmic protein, originally identified in Sinorhizobium meliloti, but widely conserved among alphaproteobacteria. Disruptions in the A. tumefaciens exoR gene result in severely compromised attachment to abiotic surfaces under static and flow conditions, and to plant tissues. These mutants are hypermucoid due to elevated production of the exopolysaccharide succinoglycan, via derepression of the exo genes that direct succinoglycan synthesis. In addition, exoR mutants have lost flagellar motility, do not synthesize detectable flagellin and are diminished in flagellar gene expression. The attachment deficiency is, however, complex and not solely attributable to succinoglycan overproduction or motility disruption. A. tumefaciens ExoR can function independently of the ChvG-ChvI two component system, implicated in ExoR-dependent regulation in S. meliloti. Mutations that suppress the exoR motility defect suggest a branched regulatory pathway controlling succinoglycan synthesis, motility and biofilm formation.
authors.affiliation: Department of Biology, Indiana University, Bloomington, IN 47405, USA.
authors.forename: Amelia D
authors.initials: AD
authors.lastname: Tomlinson
authors.affiliation: Department of Biology, Indiana University, Bloomington, IN 47405, USA.
authors.forename: Bronwyn
authors.initials: B
authors.lastname: Ramey-Hartung
authors.affiliation: Department of Biology, Indiana University, Bloomington, IN 47405, USA.
authors.forename: Travis W
authors.initials: TW
authors.lastname: Day
authors.affiliation: Department of Biology, Indiana University, Bloomington, IN 47405, USA.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Merritt
authors.affiliation: Department of Biology, Indiana University, Bloomington, IN 47405, USA.
authors.forename: Clay
authors.initials: C
authors.lastname: Fuqua
mesh_terms: D016960:Agrobacterium tumefaciens / Q000235:genetics / Q000502:physiology*; D017360:Arabidopsis / Q000382:microbiology; D001422:Bacterial Adhesion; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D018441:Biofilms; D015536:Down-Regulation; D015964:Gene Expression Regulation, Bacterial; D018517:Plant Roots / Q000382:microbiology; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis*
chemical_list: D001426:Bacterial Proteins; D011135:Polysaccharides, Bacterial; C056779:succinoglycan