Sulfur metabolism and immune-microbial networks across oral niches in periodontal disease.

Volatile sulfur compounds (VSCs) integrate microbial metabolism with local inflammation in periodontal disease. We profiled five oral niches (saliva, tongue, subgingival, supragingival, and interdental plaque) across clinical health, gingivitis, and periodontitis by combining direct VSC measurements (subgingival and oral headspace H2S/CH3SH), functional cysteine/methionine degradation assays, 16S rRNA profiling, gingival crevicular fluid cytokines, and targeted qPCR. Subgingival H2S concentrations were significantly elevated in periodontitis after adjusting for age, sex, plaque index, and subgingival bacterial load (β = 1.24, P = 0.03), and tracked shifts in community composition and the cytokine milieu. Oral headspace CH3SH increased with disease, whereas headspace H2S showed a bimodal pattern (health and periodontitis). In cysteine assays, subgingival and tongue biofilms were the most efficient H2S producers per mg protein; this ranking was preserved after normalization to total bacteria by qPCR. Metagenome predictions indicated enhanced sulfur metabolism in disease, particularly in subgingival plaque, with relative enrichment of SAM-cycle/methionine biosynthesis pathways in health. Methionine degradation to CH3SH increased with disease severity, shifting from subgingival sites in health to interdental/supragingival plaque in disease, and occurring most frequently in saliva. Correlation networks revealed niche- and diagnosis-specific coupling among VSCs, cytokines, and taxa, including associations of Capnocytophaga, Fusobacterium, Prevotella, and Corynebacterium, with IL-1β, IL-4, IL-8, and MCP-1. Together, these data identify the subgingival crevice as a disproportionate source of sulfide and show that sulfur metabolism is spatially organized and disease-responsive. We show that subgingival H2S as a functional marker that integrates microbial dysbiosis and inflammation.IMPORTANCEWe asked how metabolism, microbes, and immunity fit together during gum disease. Using a systems approach across five oral sites, we combined sulfur metabolite measurements, functional assays, microbiome profiling, and cytokine data, and analyzed them as one network. The result is a comprehensive map showing that sulfur metabolism is spatially organized, disease-responsive, and tightly coupled to local immune signals, with the subgingival niche playing an outsized role. Further, this integrated readout turns sulfur metabolism into a useful window on dysbiosis and inflammation and offers a path toward simple monitoring of periodontal disease, such as point-of-care sensors detecting subgingival hydrogen sulfide or methanethiol, or functional assays in which a methionine rinse is followed by measurement of oral headspace gases to assess microbial sulfur metabolism.