Abstract—Aiming at accurately and rapidly identifying our heavy metal resistant rhizobial strains, genomic average nucleotide identity (ANI) and core genome analyses were performed to investigate the phylogenetic relationships among 45 strains in the families of Rhizobiaceae and Bradyrhizobiaceae. The results showed that both of the ANI and core-genome phylogenetic trees revealed similar relationship. In ANI analysis, the 90%, 75% and 70% ANI values could be the thresholds for species, genus and family, respectively. Analyzing the genomes using multi-dimensional scaling and scatter plot showed highly consistent with the ANI and core-genome phylogenetic results. With these thresholds, the 45 strains were divided into 24 genomic species within the genera Agrobacterium, Allorhizobium, Bradyrhizobium, Sinorhizobium and a putative novel genus represented by Ag. albertimagni AOL15. The ten arsenite-oxidizing and antimonite tolerant strains were identified as Ag. radiobacter, and two Sinorhizobium genomic species differing from S. fredii. In addition, the description of Pararhizobium is questioned because ANI values greater than 75% were detected between P. giardinii H152T and Sinorhizobium strains. Also, reversion of the species definition for several strains in R. etli and R. leguminosarum was suggested. Our results demonstrate that analyses of ANI and core-genome are rapid and confident methods to identify the rhizobial strains, and it will be also convenient when more genome data are accumulated.
Keywords—Antimonite tolerance, arsenite-oxidation, genome, phylogeny, Rhizobia.
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