title: Endophytic occupation of peanut root nodules by opportunistic Gammaproteobacteria.
abstract: Several bacterial isolates were recovered from surface-sterilized root nodules of Arachis hypogaea L. (peanut) plants growing in soils from Córdoba, Argentina. The 16S rDNA sequences of seven fast-growing strains were obtained and the phylogenetic analysis showed that these isolates belonged to the Phylum Proteobacteria, Class Gammaproteobacteria, and included Pseudomonas spp., Enterobacter spp., and Klebsiella spp. After storage, these strains became unable to induce nodule formation in Arachis hypogaea L. plants, but they enhanced plant yield. When the isolates were co-inoculated with an infective Bradyrhizobium strain, they were even found colonizing pre-formed nodules. Analysis of symbiotic genes showed that the nifH gene was only detected for the Klebsiella-like isolates and the nodC gene could not be amplified by PCR or be detected by Southern blotting in any of the isolates. The results obtained support the idea that these isolates are opportunistic bacteria able to colonize nodules induced by rhizobia.
authors.affiliation: Departamento de Ciencias Naturales, Facultad de Ciencias Exactas, Físico-Químicas y Naturales, Universidad Nacional de Río Cuarto. Enlace Rutas 8 y 36, Km 601, 5800 Río Cuarto, Córdoba, Argentina.
authors.forename: Fernando
authors.initials: F
authors.lastname: Ibáñez
authors.forename: Jorge
authors.initials: J
authors.lastname: Angelini
authors.forename: Tania
authors.initials: T
authors.lastname: Taurian
authors.forename: María Laura
authors.initials: ML
authors.lastname: Tonelli
authors.forename: Adriana
authors.initials: A
authors.lastname: Fabra
mesh_terms: D010367:Arachis / Q000254:growth & development / Q000382:microbiology*; D001118:Argentina; D020369:Bradyrhizobium / Q000145:classification / Q000235:genetics / Q000254:growth & development*; D020563:Gammaproteobacteria / Q000145:classification* / Q000235:genetics / Q000254:growth & development*; D008969:Molecular Sequence Data; D010088:Oxidoreductases / Q000235:genetics; D010802:Phylogeny; D055170:Plant Root Nodulation; D053204:Root Nodules, Plant / Q000382:microbiology*; D017422:Sequence Analysis, DNA; D012988:Soil Microbiology
chemical_list: D010088:Oxidoreductases; C029130:nitrogenase reductase