Nandasena Kemanthi G, O'Hara Graham W, Tiwari Ravi P, Willems Anne, Howieson John G
Centre for Rhizobium Studies, Murdoch University, Murdoch, Western Australia 6160, Australia.
Int J Syst Evol Microbiol. 2009 Sep;59(Pt 9):2140-7. doi: 10.1099/ijs.0.005728-0. Epub 2009 Jul 15.
Biserrula pelecinus L. is a pasture legume that was introduced to Australia from the Mediterranean basin in 1993. Although the native rhizobial population could not nodulate B. pelecinus at the time of its introduction, recent research has shown the emergence of a diversity of strains (novel isolates) that are able to do so. Three novel isolates, WSM2073T, WSM2074 and WSM2076, had nearly identical 16S rRNA gene sequences, and clustered separately with all recognized species of the genus Mesorhizobium. Conversely, the novel isolate WSM2075T had >23 nt mismatches with the above three isolates. All four novel isolates shared 97-99% 16S rRNA gene sequence similarity with the type strains of all recognized Mesorhizobium species. However, strains WSM2073T, WSM2074 and WSM2076 showed <95.2% dnaK gene sequence similarity to the type strains of recognized Mesorhizobium species, and <92.9% to WSM2075T (which also shared <95.5% dnaK gene sequence similarity to the type strains of recognized Mesorhizobium species). Results for GSII gene sequencing were consistent with those for the dnaK gene. The fatty acid profiles of the novel isolates were diagnostic of root-nodule bacteria, but did not match those of recognized bacterial species. Strain WSM2075T had a significantly different fatty acid profile from the other three isolates. The above results indicated that strains WSM2073T, WSM2074 and WSM2076 represent the same species. Strain WSM2073T showed <45% DNA-DNA relatedness and WSM2075T<5% DNA-DNA relatedness with the type strains of recognized Mesorhizobium species; these two novel isolates shared 59% DNA-DNA relatedness. Collectively, these data indicate that strains WSM2073T, WSM2074 and WSM2076, and strain WSM2075T belong to two novel species of the genus Mesorhizobium, for which the names Mesorhizobium australicum sp. nov. and Mesorhizobium opportunistum sp. nov. are proposed, respectively. The type strain of Mesorhizobium australicum sp. nov. is WSM2073T (=LMG 24608T=HAMBI 3006T) and the type strain of Mesorhizobium opportunistum sp. nov. is WSM2075T (=LMG 24607T=HAMBI 3007T).
双节豆（Biserrula pelecinus L.）是一种豆科牧草，于1993年从地中海盆地引入澳大利亚。引入时，当地的根瘤菌种群无法使双节豆结瘤，但最近的研究表明出现了多种能够结瘤的菌株（新分离株）。三个新分离株WSM2073T、WSM2074和WSM2076具有几乎相同的16S rRNA基因序列，并与中生根瘤菌属的所有已知物种分别聚类。相反，新分离株WSM2075T与上述三个分离株有>23个核苷酸错配。所有四个新分离株与中生根瘤菌属所有已知物种的模式菌株的16S rRNA基因序列相似性为97 - 99%。然而，菌株WSM2073T、WSM2074和WSM2076与中生根瘤菌属已知物种模式菌株的dnaK基因序列相似性<95.2%，与WSM2075T的相似性<92.9%（WSM2075T与中生根瘤菌属已知物种模式菌株的dnaK基因序列相似性也<95.5%）。GSII基因测序结果与dnaK基因的结果一致。新分离株的脂肪酸谱可诊断为根瘤菌，但与已知细菌物种的脂肪酸谱不匹配。菌株WSM2075T的脂肪酸谱与其他三个分离株有显著差异。上述结果表明菌株WSM2073T、WSM2074和WSM2076代表同一物种。菌株WSM2073T与中生根瘤菌属已知物种模式菌株的DNA - DNA相关性<45%，WSM2075T<5%；这两个新分离株的DNA - DNA相关性为59%。总体而言，这些数据表明菌株WSM2073T、WSM2074和WSM2076以及菌株WSM2075T属于中生根瘤菌属的两个新物种，分别提议将其命名为澳大利亚中生根瘤菌（Mesorhizobium australicum sp. nov.）和机会主义中生根瘤菌（Mesorhizobium opportunistum sp. nov.）。澳大利亚中生根瘤菌的模式菌株是WSM2073T（=LMG 24608T=HAMBI 3006T），机会主义中生根瘤菌的模式菌株是WSM2075T（=LMG 24607T=HAMBI 3007T）。
