Nitrate as a potential prebiotic for the oral microbiome

Abstract

The salivary glands actively concentrate plasma nitrate, leading to high salivary nitrate concentrations (5-8 mM) after a nitrate-rich vegetable meal. Nitrate is an ecological factor that can induce rapid changes in structure and function of polymicrobial communities, but the effects on the oral microbiota have not been clarified. To test this, saliva of 12 healthy donors was collected to grow in vitro biofilms with and without 6.5 mM nitrate. Samples were taken at 5 h (most nitrate reduced) and 9 h (all nitrate reduced) of biofilm formation for ammonium, lactate and pH measurements, as well as 16S rRNA gene Illumina sequencing. Nitrate did not affect biofilm growth significantly, but reduced lactate production, while increasing the observed ammonium production and pH (all p < 0.01). Significantly higher levels of the oral health-associated nitrate-reducing genera Neisseria (3.1 ×) and Rothia (2.9 ×) were detected in the nitrate condition already after 5 h (both p < 0.01), while several caries-associated genera (Streptococcus, Veillonella and Oribacterium) and halitosis-and periodontitis-associated genera (Porphyromonas, Fusobacterium, Leptotrichia, Prevotella, and Alloprevotella) were significantly reduced (p < 0.05 at 5 h and/or 9 h). In conclusion, the addition of nitrate to oral communities led to rapid modulation of microbiome composition and activity that could be beneficial for the host (i.e., increasing eubiosis or decreasing dysbiosis). Nitrate should thus be investigated as a potential prebiotic for oral health.

Nitrite-producing oral microbiome in adults and children

“…Another most common bacterial genus was Veillonella, especially in the tongue coatings of children (Fig. 5), which is consistent with the findings of Doel et al The present study supports the previous findings that Neisseria was one of the predominant NO 2 − -producing bacteria in the oral cavities of adults 9,11 . Furthermore, it was the first study to show that Neisseria accounted for a relatively high percentage of NO 2 − -producing bacteria in children (Fig.…”

“…The modified agar overlay method used in the current study might be more useful for detecting NO 2 − -producing bacteria. www.nature.com/scientificreports/ Rothia is an NO 2 − -producing bacterium that is found in the oral cavity 9,12,13 . The present study showed that Rothia accounted for a high proportion of the NO 2 − -producing bacteria in children's tongue coatings (Fig.…”

“…It was not possible to explain the differences in the composition of the NO 2 − -producing bacterial populations between adults and children or among individuals in the current study, but the metabolic characteristics and networks of the oral microbiome 28 might account for these variations. Rosier et al suggested that nitrite leads to rapid modulation of microbiome in their latest report 9 , various environmental factors such as pH, oxygen concentrations in the oral cavity may also affect the bacterial composition of oral microbiome. Although it is difficult to discuss the detailed effects by these environmental factors on the differences of oral microbiome at the present stage, further study is essential.…”

“…These observations indicate that oral bacteria are involved in the production of NO 3 − from NO 2 − and that oral bacteria are essential for nitrogen oxide production and circulation. In recent years, NO 2 − has been reported to have antimicrobial effects, e.g., it suppresses the metabolism and growth of caries-and periodontal diseaserelated bacteria [6][7][8][9] , and it is also known to ameliorate cardiovascular disease by improving the systemic blood circulation 10 . These findings suggest that NO 2 − is relevant to not only oral health, but also general health.…”

Isolation and Characterization of Nitrate-Reducing Bacteria as Potential Probiotics for Oral and Systemic Health

“…Additionally, nitrate prevented acidification by oral bacteria (Li et al, 2007) and the nitrate reduction capacity (NRC) of the oral microbiota correlated negatively with caries abundance (Doel et al, 2004). Recently, Rosier et al (2020) have proposed that nitrate reduction stimulates eubiosis (i.e., an increase in health-associated species and functions) of the oral microbiota (Rosier et al, 2020). Specifically, nitrate reduction prevented acidification and the resulting overgrowth of cariogenic bacteria by increasing lactate consumption and ammonia production.…”