title: The FNR-type transcriptional regulator SinR controls maturation of Agrobacterium tumefaciens biofilms.
abstract: Agrobacterium tumefaciens is a plant pathogen that persists as surface-associated populations on plants or soil particles. A genetic screen for A. tumefaciens mutants deficient for surface interactions identified a mutant that forms thin, sparsely populated biofilms, but is proficient for initial attachment. The mutant is disrupted in a gene designated sinR, encoding a member of the DNR subfamily of FNR-type transcription regulators. SinR is required for normal maturation of A. tumefaciens biofilms on both inert surfaces and plant tissues, and elevated sinR expression results in accelerated biofilm formation. Expression of sinR is increased close to 30-fold in cultures grown in oxygen-limited environments and is also induced within biofilms grown under oxic conditions. A consensus FNR box, the presumptive binding site for FNR-type proteins, is located upstream of the sinR promoter. FnrN, a second A. tumefaciens FNR-like regulator, is required for induction of sinR in oxygen-limited cultures, whereas SinR negatively influences its own expression. FnrN influences biofilm formation, but its effects are less dramatic than those of SinR. We propose a model in which a signal cascade, responsive to oxygen limitation and initiated by FnrN, activates sinR expression in response to decreased oxygen levels, and influences the formation of A. tumefaciens biofilms.
authors.affiliation: Department of Biology, 1001 E. 3rd St., Jordan Hall 142, Indiana University, Bloomington, IN 47405-1847, USA.
authors.forename: Bronwyn E
authors.initials: BE
authors.lastname: Ramey
authors.forename: Ann G
authors.initials: AG
authors.lastname: Matthysse
authors.forename: Clay
authors.initials: C
authors.lastname: Fuqua
mesh_terms: D016960:Agrobacterium tumefaciens / Q000235:genetics / Q000502:physiology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D018441:Biofilms; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D010100:Oxygen / Q000378:metabolism; D010641:Phenotype; D010944:Plants / Q000382:microbiology; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; C095881:FnrN protein, Rhizobium leguminosarum; D012097:Repressor Proteins; D014157:Transcription Factors; C076733:FlaD protein, Bacteria; D010100:Oxygen