New insights into the relationship between the average nucleotide identity and the digital DNA-DNA hybridization values in the genus and sp. nov., a novel actinobacterium from the rhizosphere soil of , and proposal of as a synonym of based on comparative genomic analysis.

At present, it is widely believed that a 95-96% average nucleotide identity (ANI) value is equivalent to a 70% digital DNA-DNA hybridization (dDDH) value in the prokaryotic taxonomy. However, in the present study, comparative genome analysis of 29 pairs of type strains revealed that a 70% dDDH value did not correspond to a 95-96% ANI based on the MuMmer ultra-rapid aligning tool (ANIm) but approximately corresponded to a 96.6% ANIm value in the genus . Based on this corresponding relationship, phenotypic and chemotaxonomical characteristics, as well as phylogenetic analysis, an actinobacterial strain HUAS 11-8 isolated from the rhizosphere soil of , was subjected to a polyphasic taxonomic characterization. Based on EzBioCloud alignment, it was found that strain HUAS11-8 had the 16S rRNA gene similarities of 99.78% with JCM 32589, 97.8% with YIM 75904, and < 97.8% sequence similarities to other species. Phylogenetic analysis of 16S rRNA gene sequences and whole-genome sequences revealed that strain HUAS 11-8 was closely related to JCM 32589. ANIm and dDDH values between strains HUAS 11-8 and JCM 32589 were 96.3 and 68.5%, respectively, lower than the 96.6 and 70% thresholds recommended for the delineation of a novel species. Consequently, strain HUAS 11-8 should represent a novel species, for which the name sp. nov. (type strain HUAS 11-8 = MCCC 1K08337 = JCM 35980) is proposed. Furthermore, based on comparative genomic analysis and rule 42 of the Prokaryotic Code, we propose that is a later heterotypic synonym of .