Phylogenomic analysis of the duo: approaches to the origin of periodontitis.

is an oral human pathogen associated with the onset and progression of periodontitis, a chronic immune-inflammatory disease characterized by the destruction of the teeth-supporting tissue. belongs to the genus which is characterized by being composed of Gram-negative, asaccharolytic, non-spore-forming, non-motile, obligatory anaerobic species, inhabiting niches such as the oral cavity, urogenital tract, gastrointestinal tract and infected wound from different mammals including humans. Among the genus, stands out for its specificity in colonizing the human oral cavity and its keystone pathogen role in periodontitis pathogenesis. To understand the evolutionary process behind in the context of the genus, in this study, we performed a comparative genomics study with publicly available genomes, focused on four main objectives: (A) to confirm the phylogenetic position of in the genus by phylogenomic analysis; (B) the definition and comparison of the pangenomes of and its relative ; and (C) the evaluation of the gene family gain/loss events during the divergence of and ; (D) the evaluation of the evolutionary pressure (represented by the calculation of Tajima-D values and dN/dS ratios) comparing gene families of and . Our analysis found 84 high-quality assemblies representing and 14 strains (from a total of 233 genomes). Phylogenomic analysis confirmed that and are highly related lineages, close to . Both organisms harbored open pangenomes, with a strong core-to-accessory ratio for housekeeping genes and a negative ratio for unknown function genes. Our analyses also characterized the gene set differentiating from , mainly associated with unknown functions. Relevant virulence factors, such as the FimA, Mfa1, and the hemagglutinins, are conserved in and , suggesting that the origin of those factors occurred previous to the - divergence. These results suggest an unexpected evolutionary relationship between the duo and , showing more clues about the origin of the role of those organisms in periodontitis.