Effect of the host plant on the genetic diversity of a natural population of Sinorhizobium meliloti.

摘要

Soil samples were isolated from two field sites located in the European-Siberian alfalfa (Medicago sativa) gene centre. Samples were isolated from each field site in Siberia, Russia, after cultivation of wild alfalfa (M. varia) and melilot Melilotusofficinalis. Soil extracts were used to inoculate alfalfa plants. From the nodules formed after inoculation, 56 bacterial strains were isolated. Based on the data of analysis of restriction fragment length polymorphism (RFLP) of the 16S rRNA gene, thesestrains were assigned to the Sinorhizobium meliloti species. The genetic diversity of strains was characterized by means of RELP analysis using probes for symbiotic genes (nodD1 and nodABC), for symbiosis-affecting genes (leu and the cluster of exp genes), and for the recA gene. Strains isolated from different field sites and those isolated from the soil under different host plants were compared with respect to the frequency of RELP types. Statistical analysis demonstrated that the host plant is the main factor affecting the genetic diversity of nodule bacteria. Bacterial strains isolated from the soil under melilot and alfalfa differed markedly from each other in the structural organization of the symbiotic region of megaplasmid 1, which contains thenodD1ABC genes, but did not differ significantly in the structural organization of the region that contains the nodD2 gene.