Phylogenetic position of Mesorhizobium huakuii subsp rengei, a symbiont ofAstragalus sinicus cv. Japan

The phylogenetic position of Rhizobium huakuii bv. renge, a symbiont of Ast ragalus sinicus cv. Japan (renge-sou), was studied. The following phylogene tic approaches were used: restriction fragment length polymorphism (RFLP)-p olymerase chain reaction (PCR) analysis of a full-length 16S rDNA fragment, 16S rDNA analysis of the first 300-bp sequence, bacteriophage typing, and amplification of the genomic region by random primer. All the data suggest that strains of R. huakuii by. renge should be classified into subspecies o f the new genus Mesorhizobium (Jarvis et al., Inter. J. System. Bacteriol., 47, 895-898, 1997) and renamed M. huakuii subsp. rengei. All the strains f ell into a tight cluster which included M. loti and M. huakuii. The strains isolated from root nodules on A. sinicus were divided into three groups as follows: group I, M. huakuii subsp. rengei B3, M. huakuii subsp. rengei My 6, M. huakuii subsp. rengei My7, M. huakuii subsp. rengei My3, and M. huaku ii subsp. rengei OUT30020; group II, M. huakuii subsp. huakuii CCBAU103(T), M. huakuii subsp. huakuii ACCC13005, M. huakuii subsp. huakuii 7653R, and Mesorhizobium sp. N-1; group In, Mesorhizobium sp. OUT30019. All the strain s isolated in Japan except strains N-1 and OUT30019 were classified into gr oup I. Strains in group I were sensitive to bacteriophage H1 which was isol ated from rice-paddy soil in Japan. Strains in groups II and III except for M. huakuii subsp. huakuii 7653R were resistant to phage H1. Rhizobium sp. ACMP18, a native symbiont of Astragalus cicer that forms nodules on A. sini cus, showed close similarity to M. huakuii subsp. huakuii CCBAU103T, and sh ould thus be classified as a Mesorhizobium sp. Taken together, the results of the analyses indicate that M. huakuii subsp. rengei forms a subgroup whi ch is distinct from M. huakuii subsp. huakuii strains isolated in China and that strain B3 is the type strain.