title: Occurrence and diversity of nitrogen-fixing Sphingomonas bacteria associated with rice plants grown in Brazil.
abstract: So far, the occurrence of nitrogen-fixing Sphingomonas bacteria has been restricted to three strains of Sphingomonas azotifigens. In this work, a group of 46 Sphingomonas-like isolates, which originated from two rice varieties grown in two soils in Brazil, were characterized based on morphological, physiological and genetic analyses. The PCR genus specifically applied indicated that all 46 isolates belonged to the Sphingomonas genus and confirmed the results based on the yellow pigment of the colonies grown on potato agar medium and the BIOLOG data. It was also observed that 22 isolates are nitrogen-fixing bacteria as determined by the acetylene reduction method and confirmed by nifH gene detection. The genetic diversity based on the 16S rRNA analysis (amplified rDNA restriction analysis) showed that the isolates formed two distinct groups at a similarity value of 60%. Furthermore, five clusters at 60% similarity were observed with the 16S-23S intergenic space (ribosomal intergenic space analysis) analysis. Sequencing of the 16S rRNA gene and nifH fragments showed that most of the 22 nitrogen-fixing isolates formed clusters apart from that of the S. azotifigens. This is the first report on the occurrence of nitrogen-fixing Sphingomonas bacteria associated with rice grown in Brazil.
authors.affiliation: Instituto de Agronomia, CPGA-CS, Universidade Federal Rural do Rio de Janeiro, Seropédica, RJ, Brazil.
authors.forename: Sandy Sampaio
authors.initials: SS
authors.lastname: Videira
authors.forename: Jean Luiz Simões
authors.initials: JL
authors.lastname: de Araujo
authors.forename: Luciana da Silva
authors.initials: Lda S
authors.lastname: Rodrigues
authors.forename: Vera Lúcia Divan
authors.initials: VL
authors.lastname: Baldani
authors.forename: José Ivo
authors.initials: JI
authors.lastname: Baldani
mesh_terms: D001938:Brazil; D004275:DNA, Ribosomal / Q000032:analysis; D021903:DNA, Ribosomal Spacer / Q000032:analysis; D014644:Genetic Variation; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation; D012275:Oryza / Q000254:growth & development / Q000382:microbiology*; D010088:Oxidoreductases; D016133:Polymerase Chain Reaction / Q000379:methods; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012338:RNA, Ribosomal, 23S / Q000235:genetics; D015183:Restriction Mapping; D017422:Sequence Analysis, DNA; D020578:Sphingomonas / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D004275:DNA, Ribosomal; D021903:DNA, Ribosomal Spacer; D012336:RNA, Ribosomal, 16S; D012338:RNA, Ribosomal, 23S; D010088:Oxidoreductases; C029130:nitrogenase reductase