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  • Title: [Analysis of DNA homology and 16S rDNA sequence of rhizobia, a new phenotypic subgroup, isolated from Xizang Autonomous Region of China].
    Author: Wang SY, Yang XL, Li HF, Liu J.
    Journal: Wei Sheng Wu Xue Bao; 2006 Feb; 46(1):132-5. PubMed ID: 16579480.
    Abstract:
    Based on the studies of numerical taxonomy, the seven rhizobial strains isolated from the root nodules of leguminous plants Trigonella spp. and Astragalus spp. growing in the Xizang Autonomous Region of China constituted a new phenotypic subgroup, where wide phenotypic and genotypic diversity among legume crops had been reported due to complex terrain and various climate. The new phenotypic subgroup were further identified to clarify its taxonomic position by DNA homology analysis and 16S rDNA gene sequencing. The mol% G + C ratio of the DNA among members of the new subgroup ranged from 59.5 to 63.3 mol% as determined by T (m) assay. The levels of DNA relatedness, determined by using the DNA liquid hybridization method, among the members of the new subgroup were between 74.3% and 92.3%, while level of DNA relatedness between the central strains XZ2-3 of the new subgroup and the type strains of known species of Rhizobium was less than 47.4%. These results indicated that the new phenotypic subgroup is a DNA homological group different from described species of Rhizobium. Therefore, this new phenotypic subgroup was supposed to be a new species in the genus of Rhizobium since the strains in the same species generally exhibit levels of DNA homology ranging from 70 to 100%. A systematic identification method-16S rDNA gene sequence comparison was carried out to determine the phylogenetic relationships of the new subgroup with the described species of Rhizobium. The GenBank accession number for the 16S rDNA sequence of the central strain XZ2-3 of the new subgroup is DQ099745. The full-length 16S rDNA gene sequence were sequenced by chain terminator techniques and analyzed with PHYLIP. The phylogenetic trees were constructed by using the programs DRAWTREE. The phylogenetic analysis indicated that new subgroup occupy a independent sub-branch in phylogenetic tree. The sequence similarities between the center strain XZ2-3 and the closest relatives, strain R. leguminosarum USDA2370T and R. etli CFN42T, were 96.55% and 96.62% respectively. Both the 16S rDNA sequence data and the DNA relatedness data suggested that the new phenotypic subgroup isolated from the root nodules of leguminous plants Trigonella spp. and Astragalus spp. obtained from the Xizang Autonomous Region of China represents a new rhizobial species in the genus of Rhizobium according to the minimal standards for the description of new genera and species of root-and stem-nodulating bacteria.
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