Revision of the taxonomic status of type strains of Mesorhizobium loti and reclassification of strain USDA 3471T as the type strain of Mesorhizobium erdmanii sp. nov. and ATCC 33669T as the type strain of Mesorhizobium jarvisii sp. nov.

The species Mesorhizobim loti was isolated from nodules of Lotus corniculatus and its type strain deposited in several collections. Some of these type strains, such as those deposited in the USDA and ATCC collections before 1990, are not coincident with the original strain, NZP 2213T, deposited in the NZP culture collection. The analysis of the 16S rRNA gene showed that strains USDA 3471T and ATCC 33669T formed independent branches from that occupied by Mesorhizobium loti NZP 2213T and related to those occupied by Mesorhizobium opportunistum WSM2075T and Mesorhizobium huakuii IFO 15243T, respectively, with 99.9 % similarity in both cases. However, the analysis of concatenated recA, atpD and glnII genes with similarities lower than 96, 98 and 94 %, respectively, between strains USDA 3471T and M. opportunistum WSM2075T and between strains ATCC 33669T and M. huakuii IFO 15243T, indicated that the strains USDA 3471T and ATCC 33669T represent different species of the genus Mesorhizobium. These results were confirmed by DNA-DNA hybridization experiments and phenotypic characterization. Therefore, the two strains were reclassified as representatives of the two species Mesorhizobium erdmanii sp. nov. (type strain USDA 3471T = CECT 8631T = LMG 17826t2T) and Mesorhizobium jarvisii sp. nov. (type strain ATCC 33669T = CECT 8632T = LMG 28313T).