Different Mesorhizobium species sharing the same symbiotic genes nodulate the shrub legume Anagyris latifolia

The isolation and characterization of six rhizobial strains isolated from Anagyris latifolia, a shrub legume endemic to the Canary Islands, is reported in this study. The isolates were characterized by 16S-ARDRA, and sequencing of the ribosomal 16S rRNA gene, the 16S-23S rDNA intergenic spacer region, and the housekeeping gene for glutamine synthetase II (glnII). The phylogenies based on the three types of sequences matched, showing that the isolates belonged to three distinct lineages within the genus Mesorhizobium that could represent different species. However, the ribosomal and glnII phylogenies revealed some discrepancies in the relationships between the isolates and the named species in this genus. Despite their different taxonomic affiliation, all the isolates showed identical nodC sequences which were closely related (95% similarity) to that of the Mesorhizobium tianshanense type strain, indicating that they must have acquired the nodulation genes by a phenomenon of lateral gene transfer.