Reclassification of Delftia lacustris Jørgensen et al. 2009 as a Later Heterotypic Synonym of Delftia tsuruhatensis Shigematsu et al. 2003

In the present study, the taxonomic position of Delftia lacustris and Delftia tsuruhatensis was evaluated through genome analysis. The genome size of Delftia lacustris DSM 21246ᵀ was 7,267,296 bp with a G+C content of 66.1%, whereas the genome size of Delftia tsuruhatensis NBRC 16741ᵀ was 6,607,932 bp with a G+C content of 66.5%. The 16S rRNA gene sequence extracted from the genome of D. lacustris DSM 21246ᵀ showed 100% similarity to that of D. tsuruhatensis NBRC 16741ᵀ, exceeding the species delineation threshold (98.65%). In the phylogenetic and phylogenomic trees, both clustered within the same clade, indicating close evolutionary relatedness. The average nucleotide identity (ANIb) between the genomes was 97.7%, and the digital DNA–DNA hybridization (dDDH) value was 85.6%, both exceeding the accepted species delineation thresholds (95–96% for ANI and 70% for dDDH). These results support the reclassification of Delftia lacustris Jørgensen et al. 2009 as a later heterotypic synonym of Delftia tsuruhatensis Shigematsu et al. 2003.