Mesorhizobium delmotii and Mesorhizobium prunaredense are two new species containing rhizobial strains within the symbiovar anthyllidis

Roba Mohamad, Anne Willems, Antoine Le Quéré, Géraldine Maynaud, Marjorie Pervent, Maurine Bonabaud, Emeric Dubois, Jean-Claude Cleyet-Marel, Brigitte Brunel

Eight mesorhizobial symbiotic strains isolated from Anthyllis vulneraria root-nodules were studied and compared taxonomically with defined Mesorhizobium species. All strains presented identical 16S rDNA sequences but can be differentiated by multilocus sequence analysis of housekeeping genes (recA, atpD, glnII 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 Cévennes, 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 29640(T)=CFBP 8436(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.