Departamento de Ciencias Naturales, Facultad de Ciencias Exactas, Físico-Químicas y Naturales, Universidad Nacional de Río Cuarto, Córdoba, Argentina.
Microbiol Res. 2010 Aug 20;165(6):505-15. doi: 10.1016/j.micres.2009.08.004. Epub 2009 Oct 23.
In previous works we have characterized the native bacterial diversity associated with root nodules of peanut grown in Córdoba province, Argentina. Studies performed in the isolate Rhizobium sp. NET30 revealed a phylogenetic incongruence between housekeeping and nodulation genes. This discrepancy could be explained by the horizontal transfer of nodulation genes from the native peanut isolate Rhizobium sp. NCHA22, a bacterium that showed high identity percentages with Rhizobium tropici IIB strains in the basic and symbiotic genes analyzed. In this work, we demonstrate that, in R. sp. NCHA22, genes required for nodule formation in common bean (Phaseolus vulgaris L.) are plasmid-borne. A symbiotic plasmid capable of conjugal transfer to different genetic backgrounds was identified in this isolate. The mechanism involved in the plasmidic transfer differs from that described for R. tropici CIAT899 (R. tropici IIB type strain). The transfer of a symbiotic plasmid, and the subsequent homologous recombination of nodulation genes in R. sp. NET30 genetic background could account for the phylogenetic incongruence determined in this isolate. Results are also indicating that the transfer of the R. tropici NCHA22 pSym may be a frequent event in native conditions.
在以前的工作中，我们已经描述了与在阿根廷科尔多瓦省种植的花生根瘤相关的本土细菌多样性。在分离出的 Rhizobium sp. NET30 中进行的研究表明，系统发生学与管家基因和结瘤基因之间存在不一致。这种差异可以通过从本地花生分离株 Rhizobium sp. NCHA22 横向转移结瘤基因来解释，该细菌与分析的基础和共生基因中的 Rhizobium tropici IIB 菌株具有高度相似性。在这项工作中，我们证明了在 Rhizobium sp. NCHA22 中，形成菜豆（Phaseolus vulgaris L.）根瘤所需的基因是质粒携带的。在该分离株中鉴定出了一种能够在不同遗传背景下进行共轭转移的共生质粒。涉及质粒转移的机制与描述的 R. tropici CIAT899（R. tropici IIB 型菌株）不同。共生质粒的转移以及随后在 Rhizobium sp. NET30 遗传背景下结瘤基因的同源重组可能解释了在该分离株中确定的系统发生学不一致。结果还表明，R. tropici NCHA22 pSym 的转移可能是在自然条件下经常发生的事件。
