根瘤菌新类群代表菌株的16S rDNA全序列测定及其系统发育地位

SEQUENCING THE 16S rDNA OF REPRESENTATIVE STRAIN OF NEW RHIZOBIAL GROUP AND DETERMINING OF ITS PHYLOGENETIC RELATIONSHIP

用双脱氧法测定了一个根瘤菌新类群代表菌株SH2672的16S rDNA全序列,将此全序列与根瘤菌各已知种及相关种的16S rDNA全序列进行了比较及聚类分析,得到系统发育树状图。在系统发育树状图中,菌株SH2672与百脉根中慢生根瘤菌(Mesorhizobium loti),华癸中慢生根瘤菌(M. huakuii)、天山中慢生根瘤菌(M. tianshanense)、地中海中慢生根瘤菌(M. mediterraneum)、鹰嘴豆中慢生根瘤菌(M. ciceri)共同构成一个分支,与各已知种的模式菌株16S rDNA相似性分别为:96.3％,96.4％,97.2％,95.1％,95.6％,均在95％以上,它们应归属于同一属。且分支内各种间DNA同源性低于70％,表明它们分别为不同的种,菌株SH2672代表着一个新的根瘤菌种。

The full-length 16S rDNA sequence of representative strain SH2672 were sequenced by the dideoxy-mediated chain-termination method. This sequence was compared with that of type strains of all known rhizobia and related bacteria. An unrooted phylogenetic tree was produced. In this tree, strain SH2672, Mesorhizobium loti, M. huakuii, M. tianshanense, M. mediterraneum, and M. ciceri constituted a branch. Within this branch, the similarity values of 16S rDNA sequences between strain SH2672 and M. loti, M. huakuii, M. tianshanense, M. mediterraneum and M ciceri were 96.3%, 96.4%, 97.2%, 95.1% and 95.6% respectively. All similarity values was more than 95%, this indicated that these species should belong to the same genus. The values of DNA-DNA homology between type strains of these species were less than 70%, which showed that strain SH2672 (representative strain of new group) represented a new rhizobial species.