Anaerobes possess oxidative defenses found in their aerobic counterparts, as they have evolved tactics to minimize the metabolic disruption caused by O2 or restore function after oxidative stress dissipates. Notably, Methanobrevibacter species have shown substantial tolerance to O2 along with catalase activity. Recent studies revealed that Methanobrevibacter reduces O2 to H2O via F420H2 oxidase while remaining metabolically active. For example, Methanobrevibacter smithii NADH-oxidase activity, an essential enzyme in O2 detoxification with the capacity to reduce O2 to H2O. Collectively, cellular oxidative damage is multi-layered, given the diradical and oxidative nature of O2.
Despite recent insights, the enzymatic repertoire involved in protection against oxidative stress in Methanobrevibacter species associated with the human microbiome remains poorly understood. The unique microenvironment within human periodontal pockets supports the growth of anaerobes. However, given the predominant aerobic nature of the oral cavity, O2 exposure occurs during the early stages of dental plaque development, and even in already established periodontal pockets. A similar situation unfolds in the gut, where primarily anoxic conditions prevail, yet microbes are challenged with varying O2 gradients.
Shedding light on the O2 detoxifying properties of Methanobrevibacter oralis and M. smithii concerning their respective ecological niches might reveal novel adaptation strategies from an evolutionary point of view. To assess the O2 tolerance of M. oralis and M. smithii, batch bottle experiments are carried out to determine an appropriate O2 concentration for subsequent bioreactor and proteomics studies. The aim is to identify conditions in which cells face O2 stress while still exhibiting growth and metabolic activity. Preliminary findings suggest that the growth and metabolism of M. smithii are influenced by various factors, including the quantity of added O2 and the specific time point at which O2 is introduced. To substantiate these observations, the integration of proteomics data is crucial to elucidate potential adaptations of these methanogens in response to O2-induced stress.