Genomic and experimental analysis of S. dentisani 7746 demonstrates pH buffering capacity.
In the last years, microbial arginine metabolism has been extensively investigated to develop novel anti-caries strategies. Such approaches are based on the ammonia-generating capacity of some oral bacterial species to cope with the acidification cycles that continuously occur in the oral environment. Streptococcus dentisani strain 7746 was proposed as a promising probiotic against tooth decay because it is able to inhibit the growth of major oral pathogens through the production of bacteriocins, efficiently colonizes human dental plaque, and it improves several clinical features associated with oral health,  including neutralization of organic acids. In the current manuscript, we have fully sequenced and closed the genome of the probiotic strain 7746 and we have located and annotated the genes involved in arginine and agmatine degradation  We analyzed the regulation of the arginolytic pathway by transcriptomics, and performed quantitative PCR of genes involved in ammonia production from arginine and agmatine under different growth conditions in S. dentisani 7746. Finally, the addition of the probiotic strain to in vitro saliva-derived biofilms was proven to counteract the acidic pH derived from the sugar fermentation by the bacterial community. The data support the use of S. dentisani strain 7746 to reduce caries risk, by acting not only through bacteriocin production against acidogenic species but also in the pH homeostasis of the oral environment.