title: Genotypic characterization of Azotobacteria isolated from Argentinean soils and plant-growth-promoting traits of selected strains with prospects for biofertilizer production.
abstract: The genetic diversity among 31 putative Azotobacter isolates obtained from agricultural and non-agricultural soils was assessed using rep-PCR genomic fingerprinting and identified to species level by ARDRA and partial 16S rRNA gene sequence analysis. High diversity was found among the isolates, identified as A. chroococcum, A. salinestris, and A. armeniacus. Selected isolates were characterized on the basis of phytohormone biosynthesis, nitrogenase activity, siderophore production, and phosphate solubilization. Indole-3 acetic-acid (IAA), gibberellin (GA3) and zeatin (Z) biosynthesis, nitrogenase activity, and siderophore production were found in all evaluated strains, with variation among them, but no phosphate solubilization was detected. Phytohormones excreted to the culture medium ranged in the following concentrations: 2.2-18.2 μ g IAA mL(-1), 0.3-0.7 μ g GA3 mL(-1), and 0.5-1.2 μ g Z mL(-1). Seed inoculations with further selected Azotobacter strains and treatments with their cell-free cultures increased the number of seminal roots and root hairs in wheat seedlings. This latter effect was mimicked by treatments with IAA-pure solutions, but it was not related to bacterial root colonization. Our survey constitutes a first approach to the knowledge of Azotobacter species inhabiting Argentinean soils in three contrasting geographical regions. Moreover, this phenotypic characterization constitutes an important contribution to the selection of Azotobacter strains for biofertilizer formulations.
authors.affiliation: Instituto de Microbiología y Zoología Agrícola (IMYZA), Instituto Nacional de Tecnología Agropecuaria (INTA), Dr. Nicolás Repetto y De los Reseros s/n, 1686 Hurlingham, Buenos Aires, Argentina.
authors.forename: Esteban Julián
authors.initials: EJ
authors.lastname: Rubio
authors.forename: Marcela Susana
authors.initials: MS
authors.lastname: Montecchia
authors.forename: Micaela
authors.initials: M
authors.lastname: Tosi
authors.forename: Fabricio Darío
authors.initials: FD
authors.lastname: Cassán
authors.forename: Alejandro
authors.initials: A
authors.lastname: Perticari
authors.forename: Olga Susana
authors.initials: OS
authors.lastname: Correa
mesh_terms: D001118:Argentina; D001395:Azotobacter / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D016172:DNA Fingerprinting / Q000379:methods; D005308:Fertilizers / Q000382:microbiology*; D008969:Molecular Sequence Data; D063245:Plant Development; D010937:Plant Growth Regulators / Q000096:biosynthesis; D018517:Plant Roots / Q000254:growth & development; D016133:Polymerase Chain Reaction; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012988:Soil Microbiology; D014908:Triticum / Q000254:growth & development
chemical_list: D005308:Fertilizers; D010937:Plant Growth Regulators; D012336:RNA, Ribosomal, 16S