Genome-based reclassification of Sphingobacterium soli Fu et al. 2017 as a later heterotypic synonym of Sphingobacterium cellulitidis Huys et al. 2017 and proposal of Sphingobacterium siyangense subsp. siyangense subsp. nov. and Sphingobacterium siyangense subsp. cladoniae subsp. nov.

Abstract

Sphingobacterium, as the type genus of the family Sphingobacteriaceae, comprises a diverse array of species found in various environments. In this study, we aim to reassess and elucidate the taxonomic relationships of Sphingobacterium species. Based on 16S rRNA gene sequences, the phylogeny of 70 validly published Sphingobacterium species was reconstructed. Of which, 50 species with available genomes were further subjected to overall genome relatedness indices (OGRI) analysis, resulting in the identification of distinct pairs of closely related species. One such pair, consisting of the type strains of Sphingobacterium soli and Sphingobacterium cellulitidis, exhibited an average nucleotide identity (ANI) of 97.7%, a digital DNA-DNA hybridization (dDDH) of 80.1% and an average amino acid identity (AAI) of 98.3%, alongside a 16S rRNA gene sequence similarity of 99.8%. Based on the phylogenetic, OGRI and phenotypical evidence, we propose S. soli as a later heterotypic synonym of S. cellulitidis. Additionally, another pair of type strains, Sphingobacterium siyangense and Sphingobacterium cladoniae, possessed ANI, dDDH, AAI and 16S rRNA gene sequence similarity values of 96.3, 70.1, 96.0 and 99.0%, respectively. These values, together with differences in phenotypic traits, support the proposal of two subspecies within this taxonomic lineage. Thus, we propose the establishment of two new subspecies, S. siyangense subsp. siyangense subsp. nov. and S. siyangense subsp. cladoniae subsp. nov.