Polyphasic Taxonomy And Phylogeny Of Rhizobia Isolated From Melilotus In Some Regions Of Northwest

Rhizobia isolated from Melilotus,which grew in some regions of northwest, were studied by performing numerical analysis and genetic analysis such as numerical taxonomy, 16S rDNA PCR-RFLP, nodA,nifH PCR RFLP and phylogenic study (the total sequences analysis of 16S rDNA).The physiological and chemical characteristics of all isolates were tested and the results indicated all strains could use most of carbon and nitrogen. All strains have the excellent anti character to antibiotics and dye. All the test isolates were clustered into 2 branchs at the level of 92.5% by numerical taxonomy. The branchâ… consist of 56 test strains and the type strain of Rhizobium. The branchâ…¡included CCNWSX0003-1, CCNWSX0003-2, CCNWGS0008, CCNWGS0001-2, CCNWNX0025-1, type strains of S. medica and S. arboris.CCNWSX004-1 clustered with the type strain of R. leguminosarum at the level of 88%. The branchâ… was divided into 4 groups at the level of 91%. The main host plant of 23 strains was Melilotus suaveolens in group 1, that of 17 strains was M. dentatus in group 2 and that of 6 strains was M. albus in group 3. And group 4 included 3 strains from two M. dentatus and one M. suaveolens.The results showed that there were 2 genetic patterns among 63 tested strains based on analysis of 16S rDNA PCR RFLP. The typeâ… included CCNWSX0003-1,CCNWSX0003-2 and CCNWSX0004-1, which were isolates from Melilotus in the Tangzang town of Fengxian in Shaanxi. 60 strains of typeâ…¡were isolates from M. suaveolens, M. albus, M. dentatus in the regions of Shaanxi, Gansu and Ningxia, respectively.The phylogenetic positions of representative strains symbiotic with Melilotus were revealed by 16S rDNA gene sequence. It indicated that all strains separated into Rhizobium and Sinorhizobium. The representative strain CCNWSX0003-1 of type I, which fell into Rhizobium, shared 99.8% sequence homology with R. leguminosarum USDA2370. The strain CCNWGS0006 of typeâ…¡was highly related to S. meliloti at the similarity level of 100% and thus belonged to Sinorhizobium.The nodulation gene and nitrogen fixing gene were analyzed by PCR RFLP, the result showed that there were 3 and 5 different genotypes. The nodA gene of CCNWGS0006 shared 99% sequence homology with that of S. meliloti, which was the same with 16S rDNA gene sequences. And the phylogenetic positions constructed by the sequences of nifH gene had some consistency and difference with 16S rDNA gene sequences.