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 Microbacteriaceae 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 Leifsonia, Salinibacterium, Homoserinimonas, Glaciibacter, Antiquaquibacter and Diaminobutyricibacter. The findings reveal significant polyphyly in Leifsonia, Glaciibacter and Salinibacterium, indicating ecological convergence rather than shared ancestry. Proposed taxonomic revisions include the reclassification of Salinibacterium soli and Salinibacterium metalliresistens into Antiquaquibacter, Salinibacterium hongtaonis and Salinibacterium sedimenticola into Homoserinimonas, and Leifsonia psychrotolerans and Leifsonia kafniensis into Glaciibacter. Diaminobutyricibacter tongyongensis should be incorporated into Leifsonia. Additionally, Leifsonia rubra is reassigned to Salinibacterium. Two new genera were also proposed to encompass "Leifsonia flava" and Glaciibacter flavus, named Orlajensenia gen. nov. and another to encompass Leifsonia bigeumensis, named Leifsonella gen. nov. These genome-based insights provide a refined framework for the taxonomy of Microbacteriaceae, enhancing our understanding of their evolutionary and ecological roles.