Diverse genomic species and evidences of symbiotic gene lateral transfer detected among the rhizobia associated with Astragalus species grown in the temperate regions of China

Abstract

Based on the analyses of ribosomal DNA and housekeeping genes, a total of 118 bacterial isolates obtained from 13 Astragalus species grown in the temperate region of China were identified as 19 genomic species of Mesorhizobium, Rhizobium, Sinorhizobium and Bradyrhizobium, two of them being putatively new species. Phylogenetic comparison of symbiotic genes (nodC and nifH) and housekeeping genes showed that the symbiotic genes of the Astragalus rhizobia were maintained by both vertical and horizontal transfer. The results demonstrated that the Astragalus species were very promiscuous hosts for rhizobia and that their rhizobia had very diverse genomic and symbiotic gene backgrounds.