Taxonomic rearrangement of Salinibacterium, Leifsonia, Diaminobutyricibacter, Antiquaquibacter, Homoserinimonas and Glaciibacter: refining genus boundaries and proposal of two new genera – Orlajensenia gen. nov. and Leifsonella gen. nov.

The actinobacterial family <i>Microbacteriaceae</i> comprises a diverse group of Gram-positive bacteria with high G+C content and complex taxonomic challenges. Traditional polyphasic approaches, based on 16S rRNA phylogeny and phenotypic traits, have in some instances resulted in polyphyletic taxonomic groupings, necessitating genome-wide methodologies to better resolve evolutionary relationships. This study employs a taxogenomic approach - incorporating 16S rRNA gene sequencing, core protein phylogeny, average amino acid identity and percentage of conserved proteins - to reassess the genera <i>Leifsonia</i>, <i>Salinibacterium</i>, <i>Homoserinimonas</i>, <i>Glaciibacter</i>, <i>Antiquaquibacter</i> and <i>Diaminobutyricibacter</i>. The findings reveal significant polyphyly in <i>Leifsonia</i>, <i>Glaciibacter</i> and <i>Salinibacterium</i>, indicating ecological convergence rather than shared ancestry. Proposed taxonomic revisions include the reclassification of <i>Salinibacterium soli</i> and <i>Salinibacterium metalliresistens</i> into <i>Antiquaquibacter</i>, <i>Salinibacterium hongtaonis</i> and <i>Salinibacterium sedimenticola</i> into <i>Homoserinimonas</i>, and <i>Leifsonia psychrotolerans</i> and <i>Leifsonia kafniensis</i> into <i>Glaciibacter</i>. <i>Diaminobutyricibacter tongyongensis</i> should be incorporated into <i>Leifsonia</i>. Additionally, <i>Leifsonia rubra</i> is reassigned to <i>Salinibacterium</i>. Two new genera were also proposed to encompass "Leifsonia flava" and <i>Glaciibacter flavus</i>, named <i>Orlajensenia</i> gen. nov. and another to encompass <i>Leifsonia bigeumensis</i>, named <i>Leifsonella</i> gen. nov. These genome-based insights provide a refined framework for the taxonomy of <i>Microbacteriaceae</i>, enhancing our understanding of their evolutionary and ecological roles.