Rhizobium azibense sp nov., a nitrogen fixing bacterium isolated from root-nodules of Phaseolus vulgaris

Three microbial strains isolated from common beans, 23C2T (Tunisia), Gr42 (Spain) and 1E4868 (Mexico), which have been identified previously as representing a genomic group closely related to Rhizobium gallicum, are further studied here. Their 16S rRNA genes showed 98.5-99% similarity with Rhizobium loessense CCBAU 719OBT, R. gallicum R602sp(T), Rhizobium mongolense USDA 1844T and Rhizobium yanglingense CCBAU 71623(T). Phylogenetic analysis based on recA, atpD, dnaK and thrC sequences showed that the novel strains were closely related and could be distinguished from the four type strains of the closely related species. Strains 23C2(T), Gr42 and 1E4868 could be also differentiated from their closest phylogenetic neighbours by their phenotypic and physiological properties and their fatty acid contents. All three strains harboured symbiotic genes specific to biovar gallicum. Levels of DNA DNA relatedness between strain 23C2(T) and the type strains of R. loessense, R. mongolense, R. gallicum and R. yanglingense ranged from 58.1 to 61.5 Wo. The DNA Gd-C content of the genomic DNA of strain 23C2(T) was 59.52%. On the basis of these data, strains 2302(T), Gr42 and 1E4868 were considered to represent a novel species of the genus Rhizobium for which the name Rhizobium azibense is proposed. Strain 23C2(T) (=CCBAU 101087(T)=HAMB13541(T)) was designated as the type strain.