Genome-based reclassification within : Liu 2022 as a heterotypic synonym of Xu 2022 and Yang 2023 as a later heterotypic synonym of Liu 2022.

The genus comprises Gram-stain-negative, diazotrophic bacteria associated with soil and plant environments, whose taxonomic classification has not yet been thoroughly investigated. Although 16S rRNA gene-based phylogeny remains a useful preliminary tool, it often lacks the resolution needed for accurate species delineation. In this study, we conducted a comprehensive comparative genomic analysis encompassing all validly published species, integrating whole-genome phylogenomics, average nucleotide identity (ANI), digital DNA-DNA hybridization (dDDH) and other genome-based metrics to refine their classification. Phylogenetic trees constructed from 16S rRNA gene sequences and core genome alignments consistently demonstrated close genomic clustering between Red69ᵀ and RF4ᵀ, as well as between RG17ᵀ and RG2ᵀ. ANI and dDDH values for these strain pairs exceeded species delineation thresholds (>96% ANI and >70 % dDDH), strongly supporting their taxonomic unification. Despite minor phenotypic variations, genomic coherence suggests that Liu 2022 should be reclassified as Xu 2022, and Yang 2023 should be recognized as a later heterotypic synonym of Liu 2022. These findings underscore the necessity of integrating whole-genome analyses into microbial taxonomy to ensure species classifications reflect true genomic relationships.