Background: The oral cavity comprises a rich and diverse microbiome, which plays important roles in health and disease. Previous studies have mostly focused on adult populations or in very young children, whereas the adolescent oral microbiome remains poorly studied. Here, we used a citizen science approach and 16S profiling to assess the oral microbiome of 1500 adolescents around Spain and its relationships with lifestyle, diet, hygiene, and socioeconomic and environmental parameters. Results: Our results provide a detailed snapshot of the adolescent oral microbiome and how it varies with lifestyle and other factors. In addition to hygiene and dietary habits, we found that the composition of tap water was related to important changes in the abundance of several bacterial genera. This points to an important role of drinking water in shaping the oral microbiota, which has been so far poorly explored. Overall, the microbiome samples of our study can be clustered into two broad compositional patterns (stomatotypes), driven mostly by Neisseria and Prevotella, respectively. These patterns show striking similarities with those found in unrelated populations. Conclusions: We hypothesize that these stomatotypes represent two possible global optimal equilibria in the oral microbiome that reflect underlying constraints of the human oral niche. As such, they should be found across a variety of geographical regions, lifestyles, and ages.

The project was financed by CRG through Genomics and Bioinformatics Core Facilities funds, and byEduCaixa programme through funds from the Fundación Bancaria “La Caixa,” with the participation of the Center for Research into Environmental Epidemiology (CREAL), and the “Center d’Excellència Severo Ochoa 2013-2017” programme (SEV-2012-02-08) of the Ministry of Economy and Competitiveness. Eppendorf, Illumina, and ThermoFisher sponsored the research by donating some materials and reagents. David Harris Onywera was supported by a grant from the CRG-Novartis-Africa Mobility Program. TG group acknowledges support of the Spanish Ministry of Economy and Competitiveness grant BFU2015-67107 cofounded by European Regional Development Fund (ERDF); of the CERCA Programme/Generalitat de Catalunya; from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no. H2020-MSCA-ITN-2014-642095.