Wang E T, van Berkum P, Beyene D, Sui X H, Dorado O, Chen W X, Martínez-Romero E
Departmento de Genética Molecular, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico.
Int J Syst Bacteriol. 1998 Jul;48 Pt 3:687-99. doi: 10.1099/00207713-48-3-687.
The nitrogen-fixing rhizobial symbionts of Sesbania herbacea growing in the nature reserve at the Sierra de Huautla, Mexico, were isolated and characterized. All 104 isolates together with the type strain for Rhizobium galegae, HAMBI 540T, had similar 16S rRNA genes as revealed by PCR-RFLP analysis. Similarity in the sequences of the 16S rRNA genes placed the isolates on a phylogenetic branch shared with R. galegae. Among 66 randomly selected isolates, three closely related electrophoretic alloenzyme types (ETs) were identified, which were distinct from 10 ETs distinguished among 23 strains of R. galegae. A new species Rhizobium huautlense, represented by the Sesbania isolate SO2T, is proposed based upon low estimates of DNA relatedness between our chosen type strain and the type strains for the other species, the dissimilarity of the nucleotide sequence of the 16S rRNA genes, and their distinct ETs compared with R. galegae. The description of R. huautlense is significant because in the reconstruction of the phylogeny at R. huautlense there was a shift in the node of the branch of Agrobacterium vitis relative to that of R. galegae. The revised phylogenetic tree would tend to indicate common ancestry between R. galegae and Rhizobium leguminosarum.
对生长在墨西哥瓦特拉山脉自然保护区的草本田菁固氮根瘤菌共生体进行了分离和鉴定。通过PCR-RFLP分析发现，所有104株分离物与山羊豆根瘤菌模式菌株HAMBI 540T具有相似的16S rRNA基因。16S rRNA基因序列的相似性将这些分离物置于与山羊豆根瘤菌共有的系统发育分支上。在随机选择的66株分离物中，鉴定出三种密切相关的电泳同工酶类型（ETs），它们与在23株山羊豆根瘤菌中区分出的10种ETs不同。基于我们选择的模式菌株与其他物种模式菌株之间较低的DNA相关性估计、16S rRNA基因核苷酸序列的差异以及与山羊豆根瘤菌相比它们独特的ETs，提出了一个以田菁分离物SO2T为代表的新物种——瓦特拉根瘤菌。瓦特拉根瘤菌的描述具有重要意义，因为在重建瓦特拉根瘤菌的系统发育时，葡萄土壤杆菌分支的节点相对于山羊豆根瘤菌发生了偏移。修订后的系统发育树倾向于表明山羊豆根瘤菌和豌豆根瘤菌之间有共同的祖先。
