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 sequ ence analyses, DNA-DNA hybridization, restriction patterns of nodDAB and ni fH genes, and symbiotic properties. Based on the results of numerical taxon omy, 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 am orphae and Agrobacterium tumefaciens, respectively, based on their high DNA homologies with the reference strains for these species, their 16S rRNA ge ne analysis and their phenotypic features. Results of 16S rDNA PCR-RFLP ana lysis showed that cluster 9 belonged to Rhizobium. Clusters 14 and 15 were identified as Mesorhizobium based on their moderately slow-growing, acid-pr oducing characters and the high similarity of their 16S rDNA PCR-RFLP patte rns to those of Mesorhizobium species, These two clusters were genomic spec ies distinct from all described species based on analysis of DNA relatednes s within this genus. The isolates in cluster 12 (Agrobacterium tumefaciens) failed to nodulate their original host and other selected hosts and they d id not hybridize to nif or nod gene probes. The possibility of opportunisti c 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 produ ced different nodDAB RFLP patterns, but similar nifH RFLP patterns appeared tone band for each isolate). Different patterns were observed among differ ent clusters from both the nod and nif gene hybridization studies. Cross-no dulation was recorded among the isolates and the host plants in the same cl uster and promiscuous properties were found among some of the hosts tested.