Site-specialization of human oral Porphyromonas species

Site-specificity within the human oral cavity reflects adaptation mechanisms such as genome divergence and metabolic specialization. Members of the genus Porphyromonas are distributed across oral sites in health and disease, yet the specific distribution of taxa and the functional basis of their site-specificity remain poorly understood. We analyzed 1,242 metagenomes from nine oral sites in healthy individuals and 24 subgingival plaque samples from individuals with periodontitis. Competitive mapping to a dereplicated genus-level pangenome of 84 reference genomes, combined with phylogenomic, gene-level detection, and functional profiling, revealed distinct site-specific distribution patterns, ecotype differentiation, and metabolic specialization across Porphyromonas taxa. Porphyromonas pasteri was the most abundant and widespread taxon in healthy subjects, comprising two ecotypes--one mucosal, one plaque-associated. Porphyromonas gingivalis was rare in healthy subjects but present in periodontal disease, although detected in only half of periodontitis samples. P. gingivalis exhibited the broadest metabolic repertoire, suggestive of a survival strategy adaptive to disparate conditions. In contrast, Porphyromonas catoniae, restricted to healthy dental plaque, lacked biosynthetic pathways for cobalamin, biotin, and serine, implying nutritional dependency on other taxa or the host. Porphyromonas endodontalis, detected in subgingival plaque across both health and disease, also lacked several metabolic pathways. A 44 kb conjugative element identified in P. gingivalis was detected across healthy and periodontitis subgingival plaque microbiomes independently of the P. gingivalis chromosome, indicating horizontal transfer. These findings reveal genomic divergence and complex metabolic specialization among Porphyromonas taxa, refining our understanding of their role in the ecological structure of the human oral microbiome.