RESUMO
AIMS: To assess the phenotypic, symbiotic and genotypic diversity scope of Mesorhizobium spp. strains associated with Acacia seyal (Del.) isolated from different agro-ecological zones in Senegal, and uses of susceptible microbial inoculum in a reafforestation process. METHODS AND RESULTS: A polyphasic approach including phenotypic and genotypic techniques was used to study the diversity and their relationships with other biovars and species of rhizobia. The geographical origins of the strains have limited effect on their phylogenetic and phenotypic classification. Nodulation tests indicated promiscuity of the strains studied, because they were capable of nodulating six woody legume species (Acacia auriculiformis, Acacia senegal, A. seyal, Acacia tortilis ssp. raddiana, Leucaena leucocephala and Prosopis juliflora). Sequencing and phylogenetic analyses of nodA, nodC and nifH genes pointed out that in contrast to nodA gene, the phylogenies of nodC and nifH genes were not consistent with that of 16S rRNA, indicating that these genes of the A. seyal-nodulating rhizobia might have different origins. Microbial inoculation on nonsterile soil had significant effect on the nodules number and the growth of the seedlings, indicating that these strains of rhizobia might be used as inoculum. CONCLUSIONS: The results indicated that A. seyal is a nonselective host that can establish effective symbiosis with Mesorhizobium spp. strains from diverse genomic backgrounds and that the selected A. seyal-nodulating rhizobia could enhance plant growth. SIGNIFICANCE AND IMPACT OF THE STUDY: These results showed the important role that A. seyal could play in the improvement of reafforestation process as a promiscuous host, which can establish effective symbiosis with rhizobia from diverse genomic backgrounds.
Assuntos
Acacia/microbiologia , Alphaproteobacteria/genética , Filogenia , Microbiologia do Solo , Simbiose/genética , Alphaproteobacteria/classificação , Alphaproteobacteria/isolamento & purificação , Genes Bacterianos , Genes de RNAr , Genótipo , Fenótipo , Rhizobium/classificação , Rhizobium/genética , Nódulos Radiculares de Plantas/microbiologia , SenegalRESUMO
We isolated and characterized nodA genes from photosynthetic and non-photosynthetic rhizobia nodulating the legume genus Aeschynomene, and found that the nodA sequence from photosynthetic stem-nodulating bacteria was phylogenetically distant from the other already described nodA genes. Characterization of the photosynthetic strain ORS285 common nod gene cluster (nodABC) showed, upstream of nodA, the presence of a new insertion sequence element belonging to the IS3 family and specific to a group of photosynthetic strains from Aeschynomene.
Assuntos
Aciltransferases/genética , Bradyrhizobium/genética , Elementos de DNA Transponíveis , Genes Bacterianos , Fixação de Nitrogênio/genética , Fotossíntese/fisiologia , Proteínas de Bactérias , Bradyrhizobium/fisiologia , Fabaceae/microbiologia , Biblioteca Genômica , Dados de Sequência Molecular , Família Multigênica , Filogenia , Plantas Medicinais , Reação em Cadeia da Polimerase , Análise de Sequência de DNARESUMO
We investigated the presence of endophytic rhizobia within the roots of the wetland wild rice Oryza breviligulata, which is the ancestor of the African cultivated rice Oryza glaberrima. This primitive rice species grows in the same wetland sites as Aeschynomene sensitiva, an aquatic stem-nodulated legume associated with photosynthetic strains of Bradyrhizobium. Twenty endophytic and aquatic isolates were obtained at three different sites in West Africa (Senegal and Guinea) from nodal roots of O. breviligulata and surrounding water by using A. sensitiva as a trap legume. Most endophytic and aquatic isolates were photosynthetic and belonged to the same phylogenetic Bradyrhizobium/Blastobacter subgroup as the typical photosynthetic Bradyrhizobium strains previously isolated from Aeschynomene stem nodules. Nitrogen-fixing activity, measured by acetylene reduction, was detected in rice plants inoculated with endophytic isolates. A 20% increase in the shoot growth and grain yield of O. breviligulata grown in a greenhouse was also observed upon inoculation with one endophytic strain and one Aeschynomene photosynthetic strain. The photosynthetic Bradyrhizobium sp. strain ORS278 extensively colonized the root surface, followed by intercellular, and rarely intracellular, bacterial invasion of the rice roots, which was determined with a lacZ-tagged mutant of ORS278. The discovery that photosynthetic Bradyrhizobium strains, which are usually known to induce nitrogen-fixing nodules on stems of the legume Aeschynomene, are also natural true endophytes of the primitive rice O. breviligulata could significantly enhance cultivated rice production.
Assuntos
Bradyrhizobium/isolamento & purificação , Oryza/microbiologia , Sequência de Bases , Bradyrhizobium/genética , Bradyrhizobium/metabolismo , Primers do DNA/genética , Genes Bacterianos , Guiné , Dados de Sequência Molecular , Fixação de Nitrogênio , Oryza/metabolismo , Fotossíntese , Filogenia , Raízes de Plantas/microbiologia , RNA Bacteriano/genética , RNA Ribossômico 16S/genética , Senegal , Simbiose , Microbiologia da ÁguaRESUMO
A carotenoid biosynthesis gene cluster involved in canthaxanthin production was isolated from the photosynthetic Bradyrhizobium sp. strain ORS278. This cluster includes five genes identified as crtE, crtY, crtI, crtB, and crtW that are organized in at least two operons. The functional assignment of each open reading frame was confirmed by complementation studies.