Methanogenic archaea produce methane as the metabolic end product for energy conservation. Among other methanogenic pathways, the ability to produce methane from CO₂ and H₂ in hydrogenotrophic methanogenesis is the most widespread. The hydrogenotrophic species Methanobrevibacter oralis is the predominant methanogen residing in human subgingival plaque. Its prevalence has recently been linked to periodontitis, indicating a pivotal role in oral health and disease. Previous studies yielded evidence of close interactions between M. oralis and various bacterial species, as they synergistically participate in the anaerobic degradation of organic compounds. Importantly, this syntrophic cross-feeding between methanogens and hydrogen-producing bacteria, referred to as interspecies hydrogen transfer, is suggested to indirectly promote pathological conditions because it facilitates the growth and colonization of secondary fermenting pathogens. However, much is still unknown about the complex microbial interplay between M. oralis and oral community members that contribute to dysbiosis and, ultimately, to the pathogenesis of periodontitis. A more profound knowledge of the role of M. oralis within the oral microbial community is required to gain deeper insight into the etiology and manifestation of this polymicrobial disease.

In this context, we aim to gain information from three different perspectives. First, we will investigate the relationships (mutualism and competitiveness) between M. oralis and potential bacterial interaction partners through co-culturing and quantitative PCR (qPCR) techniques. Second, we will employ qPCR to quantify M. oralis in patient samples. Third, an additional information layer will be added by quantifying and visualizing M. oralis in an established biofilm model using qPCR and FISH. Ultimately, these findings will contribute to a greater understanding of the dynamic interplay between M. oralis and other oral microbes, offering valuable perspectives for developing potential therapeutic strategies against periodontal infections.