title: Large-scale transposon mutagenesis of photosynthetic Bradyrhizobium sp. strain ORS278 reveals new genetic loci putatively important for nod-independent symbiosis with Aeschynomene indica.
abstract: Photosynthetic Bradyrhizobium strains possess the unusual ability to form nitrogen-fixing nodules on a specific group of legumes in the absence of Nod factors. To obtain insight into the bacterial genes involved in this Nod-independent symbiosis, we screened 15,648 Tn5 mutants of Bradyrhizobium sp. strain ORS278 for clones affected in root symbiosis with Aeschynomene indica. From the 268 isolated mutants, 120 mutants were altered in nodule development (Ndv(-)) and 148 mutants were found to be deficient in nitrogen fixation (Fix(-)). More than 50% of the Ndv(-) mutants were found to be altered in purine biosynthesis, strengthening the previous hypothesis of a symbiotic role of a bacterial purine derivative during the Nod-independent symbiosis. The other Ndv(-) mutants were auxotrophic for pyrimidines and amino acids (leucine, glutamate, and lysine) or impaired in genes encoding proteins of unknown function. The Fix(-) mutants were found to be affected in a wide variety of cellular processes, including both novel (n = 56) and previously identified (n = 31) genes important in symbiosis. Among the novel genes identified, several were involved in the Calvin cycle, suggesting that CO(2) fixation could play an important role during this symbiosis.
authors.affiliation: Laboratoire des Symbioses Tropicales et Méditerranéennes, IRD, UMR-IRD/SupAgro/INRA/UM2/CIRAD, F-34398 Montpellier, France.
authors.forename: Katia
authors.initials: K
authors.lastname: Bonaldi
authors.forename: Benjamin
authors.initials: B
authors.lastname: Gourion
authors.forename: Joel
authors.initials: J
authors.lastname: Fardoux
authors.forename: Laure
authors.initials: L
authors.lastname: Hannibal
authors.forename: Fabienne
authors.initials: F
authors.lastname: Cartieaux
authors.forename: Marc
authors.initials: M
authors.lastname: Boursot
authors.forename: David
authors.initials: D
authors.lastname: Vallenet
authors.forename: Clémence
authors.initials: C
authors.lastname: Chaintreuil
authors.forename: Yves
authors.initials: Y
authors.lastname: Prin
authors.forename: Nico
authors.initials: N
authors.lastname: Nouwen
authors.forename: Eric
authors.initials: E
authors.lastname: Giraud
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D020369:Bradyrhizobium / Q000235:genetics* / Q000378:metabolism*; D050260:Carbohydrate Metabolism; D004734:Energy Metabolism; D007887:Fabaceae / Q000382:microbiology* / Q000502:physiology; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D016254:Mutagenesis, Insertional; D009711:Nucleotides / Q000096:biosynthesis; D010105:Oxygenases / Q000235:genetics / Q000378:metabolism; D010788:Photosynthesis / Q000235:genetics / Q000502:physiology*; D013559:Symbiosis
chemical_list: D001426:Bacterial Proteins; D009711:Nucleotides; D010105:Oxygenases; C114415:nitric oxide dioxygenase