Prevotella -dominated dysbiosis and predicted suppression of sulfur biosynthesis pathways associated with halitosis in Korean adults

ABSTRACT Halitosis affects a substantial proportion of adults worldwide, yet the compositional and functional basis of the oral microbiome in halitosis remains incompletely understood, particularly in East Asian populations. We performed 16S rRNA gene amplicon sequencing of oral gargle samples from 45 individuals with halitosis and 45 healthy controls in South Korea, generating approximately 4,600 amplicon sequence variants. Beta diversity analysis revealed significant community-level separation (PERMANOVA, P = 0.001) and an elevated Firmicutes/Bacteroidota ratio in halitosis, although alpha diversity did not differ between groups. Because the halitosis group was significantly older than controls, age-adjusted PERMANOVA and age-matched sensitivity analyses confirmed that separation persisted independent of age (age-adjusted R ² = 0.030, P = 0.003). Halitosis-associated microbiomes were enriched for Prevotella melaninogenica and Peptostreptococcus stomatis , whereas healthy microbiomes were distinguished by Haemophilus parainfluenzae and Veillonella rogosae (LEfSe). Functional profiling using PICRUSt2 revealed a counterintuitive, predicted suppression of sulfur metabolism in halitosis: pathways for sulfate assimilation, cysteine, and methionine biosynthesis were predicted to be significantly reduced relative to healthy controls. This predicted shift was significantly inversely correlated with directly measured volatile sulfur compounds (H₂S and methyl mercaptan; Spearman ρ = −0.54 and −0.64, both P < 0.0001), providing phenotypic support for the predicted signature. These findings suggest healthy oral microbiomes efficiently channel sulfur into anabolic pathways, whereas dysbiotic microbiomes may lose this capacity, allowing volatile sulfur compounds to accumulate. Our study provides a species-resolved, functionally annotated reference framework for halitosis-associated oral dysbiosis in a Korean cohort, and identifies candidate targets for diagnosis and intervention. IMPORTANCE Halitosis (bad breath) affects up to 30% of adults worldwide and is caused by volatile sulfur compounds (VSCs) produced by oral bacteria, yet the underlying microbial mechanisms remain poorly understood. Our study of 90 Korean adults reveals that halitosis is associated not only with an overgrowth of Prevotella species but also with a predicted, paradoxical suppression of the microbial community’s capacity to assimilate sulfur into anabolic biosynthetic pathways. This predicted “sulfur assimilation failure” was associated with elevated VSC accumulation, supporting a reframing of halitosis as a community-level metabolic dysfunction rather than simple bacterial overproduction. These findings have direct clinical implications: the identified Prevotella -dominated dysbiosis and associated sulfur pathway signatures represent candidate biomarkers for objective halitosis diagnosis, and the restoration of microbial sulfur-channeling capacity offers a rational target for probiotic and prebiotic interventions. This work also contributes a well-characterized oral microbiome reference data set from an underrepresented East Asian population.