Caracterização fenotípica, genotípica e simbiótica de Azorhizobium sp. de Sesbania virgata (Caz.) Pers.

Abstract

Thirty rhizobia strains with cultural characteristics on YMA similar to Azorhizobium caulinodans (alcalinization, few EPS "extracelular polissacaride production") isolated from the native leguminous species Sesbania virgata in different regions at south east Brazil (Minas Gerais and Rio de Janeiro states) were studied. Genetic, phenotypic and symbiotic characteristics were performed, including cultural and physiological tests, polyacrilamide gel electrophoresis (SDS-PAGE) of total proteins, restriction fragment length polymorphism (RFLP) of Polimerase Chain reaction (PCR) amplified 16S rDNA and intergenic space between 16S and 23S rDNA and the total sequence of bases of 16S rDNA. In Ali isolates of Azorhizobium sp. were able to fíx nitrogen in the free- living state in solid and semi-solid médium. The nitrogenase activity mesured by acetylene reduction activity was smaller than that of the strain ORS 571T of Azorhizobium caulinodans. SDS-PAGE of total proteins of all strains were relatively similar, but, small difíerences discriminated these strains into three groups. Analysis of RFLP showed differences between Azorhizobium sp. and Azorhizobium caulinodans. Total sequence of 16S rDNA shows difíerences in twenty nine different bases in BR 5401T of Azorhizobium sp. in relation to the most similar published sequence, ORS 571T Azorhizobium caulinodans. Plant infection tests to study the symbiotic relationships among Azorhizobium sp. nov BR 5401T and Sesbania virgata (Caz.) Pers with others partners were carried out in Leonardjars. When diverse legume species were inoculated with BR 5401 , only S. virgata nodulated efficiently. When Sesbania virgata was inoculated with type or reference strains of species belonging to the genera Rhizobium, Bradyrhizobium, Sinorhizobium, Mezorhizobium and Azorhizobium, nodulation occurred only with the inoculation of the homologue strain BR 5401 . It was demonstrated that this group is phenotypically and phylogenetically different from Azorhizobium caulinodans and other rhizobiaspecies described. It was also found that there is a high specific relationship, mainly concerning to nitrogen fixation, between Azorhizobium sp. BR5401T and Sesbania virgata.