RHIZOBIUM-GALLICUM SP. NOV. AND RHIZOBIUM-GIARDINII SP. NOV., FROM PHASEOLUS-VULGARIS NODULES

Thirty-one strains of two new genomic species (genomic species 1 and 2 ) of rhizobia isolated from root nodules of Phaseolus vulgaris is and originating from various locations in Prance were compared with refere nce strains of rhizobia by performing a numerical analysis of 64 pheno typic features, Each genomic species formed a distinct phenon and was separated from the other rhizobial species. A comparison of the comple te 16S rRNA gene sequences of a representative of genomic species 1 (s train R602sp(T)) and a representative of genomic species 2 (strain H15 2(T)) with the sequences of other. rhizobia and related bacteria revea led that each genomic species formed a lineage independent of the line ages formed by the previously recognized species of rhizobia, Genomic species 1 clustered with the species that include the bean-nodulating rhizobia, Rhizobium leguminosarum, Rhizobium etli, and Rhizobium tropi ci, and branched with unclassified rhizobial strain OK50, which was is olated from root nodules of Pterocarpus klemmei in Japan. Genomic spec ies 2 was distantly related to all other Rhizobium species and related taxa, and the most closely related organisms were Rhizobium galegae a nd several Agrobacterium species, On the basis of tile results of phen otypic and phylogenetic analyses and genotypic data previously publish ed and reviewed in this paper, two new species of the genus Rhizobium, Rhizobium gallicum and rhizobium giardinii, are proposed for genomic species 1 and 2, respectively, Each species could be divided in two su bgroups on the basis of symbiotic characteristics, as shown by phenoty pic (host range and nitrogen fixation effectiveness) and genotypic dat a, Far each species, one subgroup had the same symbiotic characteristi cs as R. leguminosarum biovar phaseoli and R. etli biovar phaseoli. Th e other subgroup had a species-specific symbiotic phenotype and genoty pe. Therefore, we propose that each species should be subdivided into two biovars, as follows: R, gallicum biovar gallicum and R, gallicum b iovar phaseoli; and R, giardinii biovar giardinii and R. giardinii bio var phaseoli.