Genome sequencing of the Mesorhizobium prunaredense type strain STM4891T, nodulating the legume Anthyllis vulneraria

The taxonomic position of rhizobia, like those of bacteria and archaea, is based on the notion of species which is a central concept in biology for the understanding of bacterial biodiversity and its role in ecology. In bacteriology, it relies in large part on the DNA-DNA hybridization criterion which considers that 2 bacterial strains belong to the same species if this threshold is greater than 70%. A new approach based on the comparison of the genomes of the type strains (central strains that represent the species) has been proposed to replace and consolidate the definition of a bacterial species. It is based on the estimation of indexes independent of the nomenclature and which make it possible to measure the divergence between 2 genomes. Two indices have been validated: (i) ANI (average nucleotide identity) and (ii) DDH (DNA-DNA hybridization carried out in silico). We tested this approach to define new mesorhizobial species nodulating the legume Anthyllis, with the type strain of Mesorhizobium prunaredense STM4891T.