Reclassification of strains MAFF 303099T and R7A into Mesorhizobium japonicum sp nov.

In this work we revise the taxonomic status of the Lotus-nodulating strains MAFF 303099(T) and R7A isolated in Japan and New Zealand, respectively. Their 16S rRNA gene sequences are identical and show 98.0, 99.7, 99.8 and 99.9% similarity values with respect to Mesorhizobium loti NZP 2213(T), M. jarvisii ATCC 33669(T), M. huakuii USDA 4779(T) (=CCBAU 2609(T)) and M. erdmanii USDA 3471(T), respectively. The analysis of recA and glnll gene sequeces showed that M. jarvisii ATCC 33669(T) and M. huakuii USDA 4779T (=CCBAU 2609(T)) are the most closely related strains to MAFF 303099(T) and R7A, with similarity values suggesting that these two strains belong to a different species for which MAFF 303099T is selected as the type strain. The DNA DNA relatedness values between strain MAFF 303099T and its closest phylogenetic relatives ranged from 53 to 60% in average. Strains MAFF 303099(T) and R7A presented slight differences in the proportions of C-18:1 omega 7c11-methyl and C-19:0 cyclo omega 8c fatty acids with respect to M. jarvisii ATCC 33669(T) and M. huakuii USDA 4779(T), and also in several phenotypic characteristics. Therefore, we propose the reclassification of these two strains into a novel species named Mesorhizobium japonicum sp. nov., with the type strain being MAFF 303099T (=LMG 29417(T)=CECT 9101(T)).