So R B, Ladha J K, Young J P
Division of Soil & Water Sciences, International Rice Research Institute, Manila, Philippines.
Int J Syst Bacteriol. 1994 Jul;44(3):392-403. doi: 10.1099/00207713-44-3-392.
The relationship between photosynthetic rhizobia that nodulate 10 Aeschynomene species (Aeschynomene afraspera, Aeschynomene denticulata, Aeschynomene evenia, Aeschynomene indica, Aeschynomene nilotica, Aeschynomene pratensis, Aeschynomene rudis, Aeschynomene scabra, Aeschynomene schimperi, and Aeschynomene sensitiva) and reference strains of the genera Bradyrhizobium, Rhizobium, and Azorhizobium was investigated by analyzing cellular fatty acid methyl esters (FAME) and 16S rRNA sequences. The members of each genus produced very distinct FAME patterns, and the photosynthetic rhizobia formed a subcluster in the Bradyrhizobium cluster. The absence of the cyc C19:0 type of fatty acid in all of the photosynthetic rhizobium strains isolated from 10 Aeschynomene species distinguished these microorganisms from other known rhizobia, including strain BTAi 1, a photosynthetic symbiont of A. indica. We sequenced a 264-base segment of the 16S rRNA genes of selected strains after amplification by the PCR and compared the results with previously published sequences for species of rhizobia and related photosynthetic bacteria. Photosynthetic strains IRBG 2 (from A. afraspera), IRBG 230 (from A. nilotica), and ORS 322 (from A. afraspera) had identical sequences but were distinct from strain BTAi (from A. indica) and from strain IRBG 231 (from A. denticulata), which is similar to the type strain (DNA homology group Ia) of Bradyrhizobium japonicum. Nonphotosynthetic strain IRBG 274 (from A. afraspera) was closely related to Bradyrhizobium elkanii (DNA homology group II). All of the photosynthetic rhizobia clearly fell into the Bradyrhizobium cluster. Although the results of the FAME and 16S rRNA analyses were in excellent agreement, our placement of the photosynthetic rhizobia is in apparent conflict with phenotypic data, as determined by numerical taxonomy (Ladha and So, Int. J. Syst. Bacteriol., in press) which placed the photosynthetic rhizobia in a coherent cluster that is as far from the genus Bradyrhizobium as the genera Rhizobium and Azorhizobium are. While the FAME and 16S rRNA data probably provide a more reliable indication of phylogeny, the degree of phenotypic divergence observed raises questions concerning the polyphasic approach to bacterial systematics.
通过分析细胞脂肪酸甲酯（FAME）和16S rRNA序列，研究了能使10种合萌属植物（非洲合萌、具齿合萌、埃文斯合萌、印度合萌、尼罗合萌、草地合萌、粗状合萌、粗糙合萌、施氏合萌和敏感合萌）结瘤的光合根瘤菌与慢生根瘤菌属、根瘤菌属和固氮根瘤菌属参考菌株之间的关系。每个属的成员产生非常不同的FAME模式，并且光合根瘤菌在慢生根瘤菌簇中形成一个亚簇。从10种合萌属植物中分离出的所有光合根瘤菌菌株中均不存在cyc C19:0型脂肪酸，这使这些微生物与其他已知根瘤菌区分开来，包括印度合萌的光合共生体BTAi 1菌株。我们通过PCR扩增后对选定菌株的16S rRNA基因的264个碱基片段进行了测序，并将结果与先前发表的根瘤菌和相关光合细菌物种的序列进行了比较。光合菌株IRBG 2（来自非洲合萌）、IRBG 230（来自尼罗合萌）和ORS 322（来自非洲合萌）具有相同的序列，但与BTAi菌株（来自印度合萌）和IRBG 231菌株（来自具齿合萌）不同，后者与日本慢生根瘤菌的模式菌株（DNA同源群Ia）相似。非光合菌株IRBG 274（来自非洲合萌）与埃尔卡尼慢生根瘤菌（DNA同源群II）密切相关。所有光合根瘤菌明显属于慢生根瘤菌簇。尽管FAME和16S rRNA分析结果高度一致，但我们对光合根瘤菌的分类与表型数据明显冲突，根据数值分类法（Ladha和So，《国际系统细菌学杂志》，即将发表），光合根瘤菌形成一个连贯的簇，与慢生根瘤菌属的距离与根瘤菌属和固氮根瘤菌属的距离一样远。虽然FAME和16S rRNA数据可能提供了更可靠的系统发育指示，但观察到的表型差异程度引发了关于细菌系统分类多相方法的问题。
