Evidence of horizontal transfer of symbiotic genes from a Bradyrhizobium japonicum inoculant strain to indigenous diazotrophs Sinorhizobium (Ensifer) fredii and Bradyrhizobium elkanii in a Brazilian Savannah soil
Evidence of horizontal transfer of symbiotic genes from a Bradyrhizobium japonicum inoculant strain to indigenous diazotrophs Sinorhizobium (Ensifer) fredii and Bradyrhizobium elkanii in a Brazilian Savannah soil
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DOI：
10.1128/aem.01823-06
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发表时间：
2007-04-01
影响因子：
4.4
通讯作者：
Hungria, Mariangela
中科院分区：
文献类型：
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作者：
Barcellos, Fernando Gomes;Menna, Pamela;Hungria, Mariangela
强调了水平基因转移（HGT）在细菌进化和物种形成中的重要性；然而，大多数研究都集中在致病基因聚集上，很少有关于共生岛的研究。两种大豆(甘氨酸max [L。] Merrill)和兼容的日本慢根瘤菌和elkanii慢根瘤菌菌株是巴西的外来物种，自20世纪60年代初以来已被大规模引入该国，目前占据了约45%的耕地。在过去的10年里，我们的研究小组已经获得了几个在形态、生理、遗传和共生特性方面与假定的亲本接种菌株具有高度多样性的分离株。在这项研究中，从田间种植的大豆根瘤中分离的亲本菌株和假定的自然变异株进行了遗传特征分析，包括保守基因（通过使用REP和BOX AIR引物的重复基因外回文PCR、PCR-限制性片段长度多态性和16SrRNA基因测序）、根瘤和n -2固定基因（PCR- rflp和nodY-nodA、nodC和nifH基因测序）。遗传变异是由于适应巴西塞拉多的应激环境条件和HGT事件。其中一株（s127）被鉴定为从接种剂日本芽孢杆菌中获得nodC基因的本土elkanii菌株。另一株（CPAC 402）被鉴定为本地Sinorhizobium fredii （Ensifer）菌株，该菌株从日本芽孢杆菌接种菌株中获得了整个共生岛，并保留了原始nih基因的额外拷贝。这些结果强调了细菌可能通常用于获得生态优势的策略，例如获取基因以与外来寄主豆科植物建立有效的共生关系。
The importance of horizontal gene transfer (HGT) in the evolution and speciation of bacteria has been emphasized; however, most studies have focused on genes clustered in pathogenesis and very few on symbiosis islands. Both soybean (Glycine max [L.] Merrill) and compatible Bradyrhizobium japonicum and Bradyrhizobium elkanii strains are exotic to Brazil and have been massively introduced in the country since the early 1960s, occupying today about 45% of the cropped land. For the past 10 years, our group has obtained several isolates showing high diversity in morphological, physiological, genetic, and symbiotic properties in relation to the putative parental inoculant strains. In this study, parental strains and putative natural variants isolated from field-grown soybean nodules were genetically characterized in relation to conserved genes (by repetitive extragenic palindromic PCR using REP and BOX AIR primers, PCR-restriction fragment length polymorphism, and sequencing of the 16SrRNA genes), nodulation, and N-2-fixation genes (PCR-RFLP and sequencing of nodY-nodA, nodC, and nifH genes). Both genetic variability due to adaptation to the stressful environmental conditions of the Brazilian Cerrados and HGT events were confirmed. One strain (S 127) was identified as an indigenous B. elkanii strain that acquired a nodC gene from the inoculant B. Japonicum. Another one (CPAC 402) was identified as an indigenous Sinorhizobium (Ensifer) fredii strain that received the whole symbiotic island from the B. japonicum inoculant strain and maintained an extra copy of the original nifH gene. The results highlight the strategies that bacteria may commonly use to obtain ecological advantages, such as the acquisition of genes to establish effective symbioses with an exotic host legume.