Mesorhizobial strains nodulating Anagyris latifolia and Lotus berthelotii in Tamadaya ravine (Tenerife, Canary Islands) are two symbiovars of the same species, Mesorhizobium tamadayense sp. nov.

Barranco de Tamadaya is a deep ravine located in southern Tenerife, which is included within a protected area where several endemic plants grow. Among them, two legumes are catalogued as critically endangered, Anagyris latifolia and Lotus berthelotii. Rhizobial strains isolated from their root nodules grown in soil samples from this ravine harboured symbiotic genes belonging to two distant symbiovars, but they shared identical 16S rRNA gene sequences (rrs). The phylogeny based on the rrs sequences placed these isolates in a separate subbranch that did not include any of the currently recognised Mesorhizobium species, but the resolution of the ribosomal tree did not permit further taxonomic conclusions. Nevertheless, multilocus sequence analysis (MLSA) of four housekeeping genes (atpD, recA, glnII and dnaK) and the rrs gene generated a highly supported Bayesian phylogeny, identifying these isolates as a new Mesorhizobium lineage. DNA-DNA hybridisation homology percentages were lower than 30% compared to type strains of the closest related species, and supported the phylogenetic data. Phenotypic characterisation also distinguished this lineage from the other closest Mesorhizobium species. The polyphasic approach thus confirmed that the isolates represented a novel species for which we propose the name Mesorhizobium tamadayense sp. nov. The type strain is Ala-3(T) (CECT 8040(T), LMG 26736(T)).