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In the present study, a total of 154 bacterial strains isolated from nodules of eighteen Vicia species mainly grown in the temperate Chinese provinces were characterized by ARDRA, ITS PCR-RFLP, BOX-PCR, sequencing of 16S rDNA, nodC, nifH, atpD and glnII, and nodulation tests. The results demonstrated that most of the R. leguminosarum strains were effective microsymbionts of the wild Vicia species, while genomic species related to Rhizobium gallicum, Mesorhizobium huakuii, Ensifer meliloti and Bradyrhizobium spp. were symbiotic bacteria occasionally nodulating with Vicia species. In addition, fourteen strains related to Agrobacterium, Phyllobacterium, Ensifer, Shinella and R. tropici, as well as 22 strains of R. leguminosarum might be nodule endophytes without symbiotic genes. Diverse symbiotic gene lineages were found among the test strains and a strong association was found among the symbiotic gene types and genomic species, indicating the absence of lateral gene transfer. These results greatly enlarged the rhizobial spectrum of Vicia species.

The diversity and taxonomic relationships of 83 bean-nodulating rhizobia indigenous to Ethiopian soils were characterized by PCR-RFLP of the internally transcribed spacer (ITS) region between the 16S and 23S rRNA genes, 16S rRNA gene sequence analysis, multilocus enzyme electrophoresis (MLEE), and amplified fragment-length polymorphism. The isolates fell into 13 distinct genotypes according to PCR-RFLP analysis of the ITS region. Based on MLEE, the majority of these genotypes (70%) was genetically related to the type strain of Rhizobium leguminosarum. However, from analysis of their 16S rRNA genes, the majority was placed with Rhizobium etli. Transfer and recombination of the 16S rRNA gene from presumptively introduced R. etli to local R. leguminosarum is a possible theory to explain these contrasting results. However, it seems unlikely that bean rhizobia originating from the Americas (or Europe) extensively colonized soils of Ethiopia because Rhizobium tropici, Rhizobium gallicum, and Rhizobium giardinii were not detected and only a single ineffective isolate of R. etli that originated from a remote location was identified. Therefore, Ethiopian R. leguminosarum may have acquired the determinants for nodulation of bean from a low number of introduced bean-nodulating rhizobia that either are poor competitors for nodulation of bean or that failed to survive in the Ethiopian environment. Furthermore, it may be concluded from the genetic data presented here that the evidence for separating R. leguminosarum and R. etli into two separate species is inconclusive.

Eighty-eight root-nodule isolates from Lespedeza spp. grown in temperate and subtropical regions of China were characterized by a polyphasic approach. Nine clusters were defined in numerical taxonomy and SDS-PAGE analysis of whole cell proteins. Based upon further characterizations of amplified 16S rDNA restriction analysis (ARDRA), PCR-based restriction fragment length polymorphism of ribosomal IGS, 16S rDNA sequence analysis and DNA-DNA hybridization, these isolates were identified as Bradyrhizobium japonicum, B. elkanii, B. yuanmingense, Mesorhizobium amorphae, M. huakuii, Sinorhizobium meliloti and three genomic species related to B. yuanmingense, Rhizobium gallicum and R. tropici. The Bradyrhizobium species and R. tropici-related rhizobia were mainly isolated from the subtropical region and the species of Mesorhizobium, S. meliloti and R. gallicum-related species were all isolated from the temperate region. Phylogenetic analyses of nifH and nodC indicated that the symbiotic genes of distinct rhizobial species associated with Lespedeza spp. might have different origins and there was no evidence for lateral gene transfer of symbiotic genes. The results obtained in the present study and in a previous report demonstrated that Lespedeza spp. are nodulated by rhizobia with diverse genomic backgrounds and these Lespedeza-nodulating rhizobia were not specific to the host species, but specific to their geographic origins.