Résumé
Eight mesorhizobial symbiotic strains isolated from Anthyllis vulneraria root-nodules were studied and compared taxonomically with defined Mesorhizobium species. All strains presented identical 165 rDNA sequences but can be differentiated by multilocus sequence analysis of housekeeping genes (recA, atpD, glnll and dnaK). Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry analyses separate these strains in two groups and a separate strain. Levels of DNA-DNA relatedness were less than 55% between representative strains and their closest Mesorhizobium reference relatives. The two groups containing four and three strains, respectively, originating from border mine and non-mining areas in Cevennes, were further phenotypically characterized. Groupings were further supported by average nucleotide identity values based on genome sequencing, which ranged from 80 to 92% with their close relatives and with each other, confirming these groups represent new Mesorhizobium species. Therefore, two novel species Mesorhizobium delmotii sp. nov. (type strain STM4623(T) = LMG 296401(T)= CFBP 84361(T) ) and Mesorhizobium prunaredense sp. nov. (type strain STM4891(T) = LMG 29641(T) = CFBP 8437(T)) are proposed. Type strains of the two proposed species share accessory common nodulation genes within the new symbiovar anthyllidis as found in the Mesorhizobium metallidurans type strain.