title: Novel mixed-linkage β-glucan activated by c-di-GMP in Sinorhizobium meliloti.
abstract: An artificial increase of cyclic diguanylate (c-di-GMP) levels in Sinorhizobium meliloti 8530, a bacterium that does not carry known cellulose synthesis genes, leads to overproduction of a substance that binds the dyes Congo red and calcofluor. Sugar composition and methylation analyses and NMR studies identified this compound as a linear mixed-linkage (1 → 3)(1 → 4)-β-D-glucan (ML β-glucan), not previously described in bacteria but resembling ML β-glucans found in plants and lichens. This unique polymer is hydrolyzed by the specific endoglucanase lichenase, but, unlike lichenan and barley glucan, it generates a disaccharidic → 4)-β-D-Glcp-(1 → 3)-β-D-Glcp-(1 → repeating unit. A two-gene operon bgsBA required for production of this ML β-glucan is conserved among several genera within the order Rhizobiales, where bgsA encodes a glycosyl transferase with domain resemblance and phylogenetic relationship to curdlan synthases and to bacterial cellulose synthases. ML β-glucan synthesis is subjected to both transcriptional and posttranslational regulation. bgsBA transcription is dependent on the exopolysaccharide/quorum sensing ExpR/SinI regulatory system, and posttranslational regulation seems to involve allosteric activation of the ML β-glucan synthase BgsA by c-di-GMP binding to its C-terminal domain. To our knowledge, this is the first report on a linear mixed-linkage (1 → 3)(1 → 4)-β-glucan produced by a bacterium. The S. meliloti ML β-glucan participates in bacterial aggregation and biofilm formation and is required for efficient attachment to the roots of a host plant, resembling the biological role of cellulose in other bacteria.
authors: Departamento Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, 18008 Granada, Spain;
authors: Daniel
authors: D
authors: Pérez-Mendoza
authors: Departamento Química Orgánica, Facultad de Química, Universidad de Sevilla, 41001 Sevilla, Spain; and.
authors: Miguel Ángel
authors: MÁ
authors: Rodríguez-Carvajal
authors: Departamento Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, 18008 Granada, Spain;
authors: Lorena
authors: L
authors: Romero-Jiménez
authors: Departamento Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, 18008 Granada, Spain;
authors: Gabriela de Araujo
authors: Gde A
authors: Farias
authors: Departamento Biología, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 Madrid, Spain.
authors: Javier
authors: J
authors: Lloret
authors: Departamento Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, 18008 Granada, Spain;
authors: María Trinidad
authors: MT
authors: Gallegos
authors: Departamento Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, 18008 Granada, Spain; Juan.Sanjuan@eez.csic.es.
authors: Juan
authors: J
authors: Sanjuán
mesh_terms: D002240:Carbohydrate Sequence; D002855:Chromatography, Thin Layer; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000378:metabolism; D000455:Medicago sativa / Q000382:microbiology; D008969:Molecular Sequence Data; D009876:Operon; D010802:Phylogeny; D018517:Plant Roots / Q000382:microbiology; D016133:Polymerase Chain Reaction; D011509:Proteoglycans / Q000737:chemistry / Q000378:metabolism*; D018125:Receptors, Transforming Growth Factor beta / Q000737:chemistry / Q000378:metabolism*; D016962:Sinorhizobium meliloti / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D011509:Proteoglycans; D018125:Receptors, Transforming Growth Factor beta; C071736:betaglycan; C062025:bis(3',5')-cyclic diguanylic acid; D006152:Cyclic GMP
keywords: cyclic diguanylate; exopolysaccharides; plant–microbe interactions
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