Sinorhizobium morelense sp. nov. is described to designate a group of bacteria isolated from root nodules of Leucaena leucocephala. S. morelense shows 98% 16S rRNA gene sequence similarity to some Sinorhizobium species and to Ensifer adhaerens. This novel species is distinguished from other Sinorhizobium species and from E. adhaerens by DNA–DNA hybridization, 16S rRNA gene restriction fragments and sequence and some distinctive phenotypic features. Strains of this species are highly resistant to some antibiotics, such as carbenicillin (1 mg mlN1), kanamycin (500 lgmlN1) and erythromycin (300 lgmlN1). They do not form nodules, but a nodulating strain, Lc57, is closely related to the novel species. Strain Lc04T (=LMG 21331T= CFN E1007T) is designated as the type strain of this novel species.

Forty-eight rhizobial isolates from root nodules of Indigofera and Kummerowia, two genera of annual or perennial wild legumes growing in the Loess Plateau in north-western China, were characterized by a polyphasic approach. Two main groups, cluster 1 and cluster 2, were defined based upon the results of numerical taxonomy, SDS-PAGE of whole-cell proteins and DNA relatedness. All the isolates within cluster 1 were isolated from Indigofera and they were identified as Rhizobium strains by 16S rRNA gene analysis. DNA relatedness of 29<5–48<9% was obtained among the cluster 1 isolates and the reference strains for defined Rhizobium species. Cluster 2 consisted of isolates from Kummerowia stipulacea and was identified as belonging to Sinorhizobium by 16S rRNA gene analyses. DNA relatedness varied from 5<2 to 41<7% among the isolates of cluster 2 and reference strains for Sinorhizobium species. Considering the existence of distinctive features among these two groups and related species within the genera Rhizobium and Sinorhizobium, we propose two novel species, Rhizobium indigoferae sp. nov. for cluster 1, with isolate CCBAU 71714T (=AS 1.3046T) as the type strain, and Sinorhizobium kummerowiae sp. nov. for cluster 2, with isolate CCBAU 71042T (=AS 1.3045T) as the type strain.

糖蜜草（Melinisminutiflora Beauv.）是热带地区的一种优良牧草。采用选择性培养基在厌氧和好氧两种培养条件下，从糖蜜草根、茎中都可分离得到具有较强固氮酶活性的菌株。通过SDS2PAGE全细胞蛋白电泳技术快速聚类分析表明，来源于糖蜜草中的菌株为同一类群。16SrDNA序列分析和总DNA的G+C%含量进一步确定糖蜜草中所分离的菌株属于固氮螺菌属（Azospirillum），与产脂固氮螺菌（Azospirillumlipoferum）亲缘关系较近。BIOLOG板测定结果显示,糖蜜草菌株TMCY243对多种碳源具有很强的适应性,与产脂固氮螺菌（A.lipoferum）的模式菌株DSM1691存在着较大的差异。以上结果表明，糖蜜草内生固氮菌为固氮螺菌属的一个新类群。

采用插入序列指纹图谱分析（IS2PCR）和16SrRNA基因全序列分析，对来源于优良牧草——糖蜜草Melini sminuti flora Beauv。内生固氮菌进行研究。结果表明，糖蜜草中分离的内生固氮菌与产脂固氮螺菌模式菌株DSM1691的插入序列指纹图谱存在着差异;来源于糖蜜草的4株菌紧密地聚在一起，与GenBank中已知产脂固氮螺菌Azospirillum lipo ferum的16SrRNA基因全序列有97%的序列相似性。初步确定糖蜜草中分离的内生固氮菌为一新类群的内生固氮菌。

通过rRNA基因内转录间隔区的碱基序列分析，对中华根瘤菌属Sinorhizobium、慢生根瘤属Bradyrhizobium和中慢生根瘤菌属Mesorhizobium种间亲缘关系十分密切的菌株进行区分。结果表明，rRNA基因间隔区序列能很好地区分种间亲缘关系十分密切的菌株。用rRNA基因间隔区序列构建的系统发育树与rRNA基因序列构建的系统发育树结果十分相似。