RESUMEN
Members of the genus Bradyrhizobium are well-known as nitrogen-fixing microsymbionts of a wide variety of leguminous species, but they have also been found in different environments, notably as endophytes in non-legumes such as sugarcane. This study presents a detailed polyphasic characterization of four Bradyrhizobium strains (type strain BR 10280T), previously isolated from roots of sugarcane in Brazil. 16S rRNA sequence analysis, multilocus sequence analysis (MLSA) and analysis of the 16S-23S rRNA internal transcribed spacer showed that these strains form a novel clade close to, but different from B. huanghuaihaiense strain CCBAU 23303T. Average nucleotide identity (ANI) analyses confirmed that BR 10280T represents a novel species. Phylogenetic analysis based on nodC gene sequences also placed the strains close to CCBAU 23303T, but different from this latter strain, the sugarcane strains did not nodulate soybean, although they effectively nodulated Vigna unguiculata, Cajanus cajan and Macroptilium atropurpureum. Physiological traits are in agreement with the placement of the strains in the genus Bradyrhizobium as a novel species for which the name Bradyrhizobium sacchari sp. nov. is proposed.
Asunto(s)
Bradyrhizobium , Fabaceae/microbiología , Nódulos de las Raíces de las Plantas/microbiología , Técnicas de Tipificación Bacteriana , Composición de Base/genética , Bradyrhizobium/clasificación , Bradyrhizobium/genética , Bradyrhizobium/aislamiento & purificación , Brasil , Cajanus/microbiología , ADN Bacteriano/genética , Ácidos Grasos/análisis , Genes Bacterianos/genética , Tipificación de Secuencias Multilocus , Fijación del Nitrógeno/fisiología , Hibridación de Ácido Nucleico , Phaseolus/microbiología , Filogenia , ARN Ribosómico 16S/genética , Saccharum/microbiología , Análisis de Secuencia de ADN , Glycine max/microbiología , Simbiosis , Vigna/microbiologíaRESUMEN
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.