[Analysis of 16S rDNA sequence and DNA-DNA hybridization of rhizobia isolated from Indigofera sp].

Based on the previous studies on numerical taxonomy and SDS-PAGE of whole-cell protein, the rhizobia strains isolated from Indigofera sp. in loess plateau area of North-west China constituted a new cluster, the 16S rDNA sequence of representative strain SHL042 was tested, and the phylogenetic tree was produced. In this tree, the strain SHL042, R. tropici A, R. tropici B, R. leguminosarum, R. etli, R. hananesis, R. mongolense and R. gallicum constituted a branch of phylogenetic. Within this branch, the similarity values of 16S rDNA sequences were 95.4%, 95.5%, 96.3%, 95.8%, 96.3%, 97.9% and 97.7% respectively. The values were more than 95%. This indicated that these species should belong to the same genus. The values of DNA homology in the new cluster were all more than 80%, but the values between SHL042 and the strains of these species were less than 50%. Thus, the strain SH714 represented a new rhizobia species.

[Study on intergenera fusion of protoplasts from Rhizobium leguminosorum and Sinorhizobium xinjiangnesis].

Penicillin and chloromycetin were regarded as the sign of resistance to antibodies of R. leguminosorum USDA2370 and S. xinjiangnesis CCBAU110 respectively. Using the protoplast fusion technique, USDA2370 and CCBAU110 were successfully fused. Fusion hybrid can inoculate in the leguminous of parental strains respectively. There were apparent differences between parents and fusion hybrid in cell morphology, colony and pattern of whole-cell protein. The values of DNA homology between fusion hybrid and USDA2370 and CCBAU110 were 56.6% and 10.2% respectively.

Characterization of bacteria isolated from wild legumes in the north-western regions of China.

Nodule isolates from 11 species of wild legumes in north-western China were characterized by numerical taxonomy, PCR-based 16S rRNA gene RFLP and sequence analyses, DNA-DNA hybridization, restriction patterns of nodDAB and nifH genes, and symbiotic properties. Based on the results of numerical taxonomy, most of the 35 new isolates were grouped into five clusters (clusters 7, 9, 12, 14 and 15). Clusters 7 and 12 were identified as Mesorhizobium amorphae and Agrobacterium tumefaciens, respectively, based on their high DNA homologies with the reference strains for these species, their 16S rRNA gene analysis and their phenotypic features. Results of 16S rDNA PCR-RFLP analysis showed that cluster 9 belonged to Rhizobium. Clusters 14 and 15 were identified as Mesorhizobium based on their moderately slow-growing, acid-producing characters and the high similarity of their 16S rDNA PCR-RFLP patterns to those of Mesorhizobium species. These two clusters were genomic species distinct from all described species based on analysis of DNA relatedness within this genus. The isolates in cluster 12 (Agrobacterium tumefaciens) failed to nodulate their original host and other selected hosts and they did not hybridize to nif or nod gene probes. The possibility of opportunistic nodulation of these isolates is discussed. Identical restriction patterns were obtained in the nif or nod gene hybridization studies from the three isolates within cluster 15, which were isolated from the same host species. The isolates from different host plants in each of clusters 9 and 14 produced different nodDAB RFLP patterns, but similar nifH RFLP patterns appeared (one band for each isolate). Different patterns were observed among different clusters from both the nod and nif gene hybridization studies. Crossnodulation was recorded among the isolates and the host plants in the same cluster and promiscuous properties were found among some of the hosts tested.