The genus Micromonospora has been identified in nodules of many legumes and some new species of this genus have been isolated from these plant organs. In this study we analysed the taxonomic diversity of Micromonospora strains isolated from alfalfa nodules in Spain and Australia on the basis of 3 phylogenetic markers, the rrs and gyrB genes and 16S-23S intergenic spacer (ITS). The genome evaluation of chosen strains representative of distinct clusters or lineages identified soon after rrs, gyrB and ITS analyses confirmed the benefits obtained with these phylogenetic markers. They showed that the analysed strains belong to at least 18 Micromonospora species which includes previously described ones, such as Micromonospora noduli, Micromonospora ureilytica, Micromonospora taraxaci, Micromonospora zamorensis, Micromonospora aurantiaca and Micromonospora tulbaghiae. Most of these strains belong to undescribed species of Micromonospora displaying the higher taxonomic diversity of strains from this genus inhabiting alfalfa nodules. Even though Micromonospora strains are not in a position to induce the formation of these nodules, and it appears that they do not contribute to repair atmospheric nitrogen, they could play a part connected with the mechanisms of plant development promotion and pathogen protection presented by Micromonospora strains isolated from legume nodules.
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