Abstract：
As a legume crop widely cultured in the world, faba bean (Vicia faba L.) forms root nodules with diverse Rhizobium species in different regions. However, the symbionts associated with this plant in Mexico have not been studied. To investigate the diversity and species/symbiovar affiliations of rhizobia associated with faba bean in Mexico, rhizobia were isolated from this plant grown in two Mexican sites in the present study. Based upon the analysis of recA gene phylogeny, two genotypes were distinguished among a total of 35 isolates, and they were identified as Rhizobium hidalgonense and Rhizobium redzepovicii, respectively, by the whole genomic sequence analysis. Both the species harbored identical nod gene cluster and the same phylogenetic positions of nodC and nifH. So, all of them were identified into the symbiovar viciae. As a minor group, R. hidalgonense was only isolated from slightly acid soil and R. redzepovicii was the dominant group in both the acid and neutral soils. In addition, several genes related to resistance to metals (zinc, copper etc.) and metalloids (arsenic) were detected in genomes of the reference isolates, which might offer them some adaptation benefits. As conclusion, the community composition of faba bean rhizobia in Mexico was different from those reported in other regions. Furthermore, our study identified sv. viciae as the second symbiovar in the species R. redzepovicii. These results added novel evidence about the co-evolution, diversification and biogeographic patterns of rhizobia in association with their host legumes in distinct geographic regions.
摘要：
作为世界上广泛种植的豆类作物，蚕豆（ViciafabaL.）在不同地区形成具有不同根瘤菌种类的根瘤。然而,与墨西哥这种植物相关的共生体尚未被研究。为了调查墨西哥与蚕豆相关的根瘤菌的多样性和物种/共生关系，在本研究中，根瘤菌是从生长在两个墨西哥地点的该植物中分离出来的。基于recA基因系统发育分析，在总共35个分离株中区分了两种基因型，它们被鉴定为根瘤菌和红根瘤菌，分别,通过全基因组序列分析。这两个物种都具有相同的nod基因簇以及nodC和nifH的相同系统发育位置。所以,它们都被鉴定为共生体。作为一个小团体，R.hidalgonense仅从弱酸性土壤中分离出来，而R.redzepovicii是酸性和中性土壤中的优势群。此外,几个与金属抗性相关的基因(锌，铜等)和类金属(砷)在参考分离株的基因组中检测到，这可能会给他们带来一些适应的好处。作为结论，墨西哥蚕豆根瘤菌的群落组成与其他地区报道的不同。此外，我们的研究确定了sv。viciae是R.redzepovicii物种中的第二个共生生物。这些结果增加了关于共同进化的新证据，根瘤菌的多样化和生物地理模式及其在不同地理区域的寄主豆科植物。
