Polyphasic Taxonomy Of Rhizobia Isolated From Hedysarum Spp. And Lotus Spp. Grown In Some Regions Of China

This thesis reviewed the historical development, the current taxonomic status and the phylogeny of rhizobia, and main methods applied in rhizobial polyphasic taxonomy. 42 rhizobia isolated from Hedysarum spp. and Lotus spp. in various geographical regions of China were studied together with the reference strains of some recognized rhizobial species by performing polyphasic taxonomy, including numerical taxonomy, 16S rDNA PCR-RFLP, BOX-PCR fingerprinting, DNA base composition and DNA-DNA hybridization.Six groups could be clustered at the similarity level of 83% on the basis of numerical taxonomy. Group 1, 2, 4 and 5 each consisted of one or two known reference strains; however, group 3, 6 didn't contain any known reference strains.The dendrograms derived from PCR-RFLP of 16S rDNA and BOX-PCR fingerprinting were generally agreement with that of numerical analysis of phenotypic characteristics. BOX-PCR fingerprinting is more appropriate using as a method revealing genotypic diversity within a rhizobial species.Full length of 16S rDNA gene of CCBAU 61009 was sequenced and compared with that of the known sequences in GenBank, the result showed that the 16S rDNA sequence of CCBAU 61009 was the same as that of Mesorhizobium amorphae ACCC196651. The results of DNA G+C mol% and DNA-DNA relatedness indicated that group I was Sinorhizobium fredii and group 6 was Mesorhizobium amorphae.The phenotypic characterization of the strains showed that most of the rhizobial strains isolated from Hedysarum spp. had high stress resistance. The resistance of these strains to the reverse conditions might be the results of their adaptation to the environments because these bacteria were obtained from hosts grown in the soils that are dry, alkaline-saline, and poor in organic materials.