The genetic and phylogenetic relationships for strains of Mesorhizobium tianshanense and its relatives were compared by an analysis of the results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDSPAGE) of whole-cell proteins, DNA-DNA hybridization, and full 16s rRNA gene sequencing. The strains of M. tianshanense formed a cluster which was distinct from those of other rhizobium species in the clustering analysis of SDS-PAGE. DNA-DNA relatedness between A-1BS (type strain of M. tianshanense) and the type or eference strains for Mesorhizobium loti, M. huakuii, M. ciceri, M. mediterraneum, and cluster U, an unnamed hizobial group, ranged from 4.4 to 43.8%. The phylogenetic analysis based on the 16s rRNA gene sequences howed that M. tianshunense was closely related to the Mesorhizobium phylogenetic branch and could be istinguished from the other four species in this branch. These results further confirmed that these bacteria onstitute a distinct rhizobial species.

Twenty-nine rhizobial isolates from root nodules of Astragalus and Lespedeza spp. growing in the Loess Plateau of China were characterized by numerical taxonomy, RFLP and sequencing of PCR-amplified 16S rRNA genes, measurement of DNA G+C content, DNA–DNA relatedness and cross-nodulation with selected legume species. Based on the results of numerical taxonomy, the isolates formed two clusters (1 and 2) with some single isolates at a similarity level of 82 %. Cluster 1 contained six isolates from Astragalus and Lespedeza spp. Cluster 2 consisted of nine isolates from Astragalus spp. DNA relatedness was greater than 80% among isolates within cluster 2. Phylogenetic analysis based on 16S rRNA gene sequences showed that CCBAU 7190BT, representing cluster 2, was closely related to Rhizobium galegae and Rhizobium huautlense. DNA–DNA relatedness between CCBAU 7190BT and reference strains of R. galegae, R. huautlense and other related species ranged from 0 to 48?6 %. The cluster 2 isolates could also be differentiated phenotypically from related species. Based on these data, a novel species, Rhizobium loessense sp. nov., is proposed for cluster 2, with the type strain CCBAU 7190BT (=AS1.3401T=LMG 21975T).

Sinorhizobium morelense sp. nov. is described to designate a group of bacteria isolated from root nodules of Leucaena leucocephala. S. morelense shows 98% 16S rRNA gene sequence similarity to some Sinorhizobium species and to Ensifer adhaerens. This novel species is distinguished from other Sinorhizobium species and from E. adhaerens by DNA–DNA hybridization, 16S rRNA gene restriction fragments and sequence and some distinctive phenotypic features. Strains of this species are highly resistant to some antibiotics, such as carbenicillin (1 mg mlN1), kanamycin (500 lgmlN1) and erythromycin (300 lgmlN1). They do not form nodules, but a nodulating strain, Lc57, is closely related to the novel species. Strain Lc04T (=LMG 21331T= CFN E1007T) is designated as the type strain of this novel species.

Eight fast-growing rhizobial isolates from Xinjiang soils were identified as Sinorhizobium xinjiangense by analyses of 16S rRNA gene sequences, SDSPAGE of proteins, intergenic spacer sequences and DNA–DNA hybridization. Based on all of the results, these isolates and the reference strains for S. xinjiangense were a distinct genomic species, although the 16S rRNA genes were closely related to that of Sinorhizobium fredii.

Forty-eight rhizobial isolates from root nodules of Indigofera and Kummerowia, two genera of annual or perennial wild legumes growing in the Loess Plateau in north-western China, were characterized by a polyphasic approach. Two main groups, cluster 1 and cluster 2, were defined based upon the results of numerical taxonomy, SDS-PAGE of whole-cell proteins and DNA relatedness. All the isolates within cluster 1 were isolated from Indigofera and they were identified as Rhizobium strains by 16S rRNA gene analysis. DNA relatedness of 29<5–48<9% was obtained among the cluster 1 isolates and the reference strains for defined Rhizobium species. Cluster 2 consisted of isolates from Kummerowia stipulacea and was identified as belonging to Sinorhizobium by 16S rRNA gene analyses. DNA relatedness varied from 5<2 to 41<7% among the isolates of cluster 2 and reference strains for Sinorhizobium species. Considering the existence of distinctive features among these two groups and related species within the genera Rhizobium and Sinorhizobium, we propose two novel species, Rhizobium indigoferae sp. nov. for cluster 1, with isolate CCBAU 71714T (=AS 1.3046T) as the type strain, and Sinorhizobium kummerowiae sp. nov. for cluster 2, with isolate CCBAU 71042T (=AS 1.3045T) as the type strain.