The tongue biofilm metatranscriptome identifies metabolic pathways associated with the presence or absence of halitosis suggests a recent study published in the NPJ Biofilms Microbiomes.
In the present study, researchers analyzed the composition and gene expression of the active tongue microbiota in halitosis-free individuals and halitosis patients using a metatranscriptomic approach. As this condition is the consequence of VSCs production, we measured the concentration of these gases and placed volunteers in four groups based on their VSC profiles. Independently of the group, the composition of the tongue microbiota detected in this study presented similarities to previously reported tongue communities by other authors.

Halitosis is a highly prevalent condition characterized by oral malodor. A Swedish study with more than 800 participants showed a 2% prevalence, while in a Chinese population with 2500 participants the estimated proportion increased up to 27.5%. A recent systematic revision estimated a 31.8% prevalence of halitosis after examining 548 publications. Depending on the origin of the oral malodor, halitosis can be differentiated into intra-oral (90% of cases), extra-oral and transient halitosis
Intra-oral halitosis usually results from the production of volatile sulfur compounds, such as methyl mercaptan and hydrogen sulfide, by the tongue microbiota. There are currently no reports on the microbial gene-expression profiles of the tongue microbiota in halitosis. In this study, we performed RNAseq of tongue coating samples from individuals with and without halitosis.
The activity of Streptococcus (including S. parasanguinis), Veillonella (including V. dispar) and Rothia (including R. mucilaginosa) was associated with halitosis-free individuals while Prevotella (including P. shahi), Fusobacterium (including F. nucleatum) and Leptotrichia were associated with halitosis. Interestingly, the metatranscriptome of patients that only had halitosis levels of methyl mercaptan was similar to that of halitosis-free individuals.
Finally, gene expression profiles showed a significant over-expression of genes involved in L-cysteine and L-homocysteine synthesis, as well as nitrate reduction genes, in halitosis-free individuals and an over-expression of genes responsible for cysteine degradation into hydrogen sulfide in halitosis patients.
Reference:
Carda-Diéguez, M., Rosier, B., Lloret, S. et al. The tongue biofilm metatranscriptome identifies metabolic pathways associated with the presence or absence of halitosis. npj Biofilms Microbiomes 8, 100 (2022). https://doi.org/10.1038/s41522-022-00364-2