Insights into ammonia adaptation and methanogenic precursor oxidation by genome-centric analysis

Ammonia released from degradation of protein and/or urea usually leads to suboptimal anaerobic digestion when N-rich organic waste is used. However, the insights behind differential ammonia tolerance of anaerobic microbiomes remain an enigma. In this study, the cultivation in synthetic medium with different carbon sources (acetate, methanol, formate, H2/CO2) shaped a common initial inoculum into four unique ammonia-tolerant syntrophic populations. Specifically, various levels of ammonia tolerance were observed: consortia fed with methanol and H2/CO2 could grow at ammonia levels up to 7.25 g NH4+-N/L, the other two groups, ( formate and acetate), only thrived at 5.25 and 4.25 g NH4+-N/L, respectively. Metabolic reconstruction highlighted this divergent microbiome might be achieved by complementary metabolisms to maximize biomethane recovery from carbon sources, thus indicating the importance of the syntrophic community in AD of N-rich substrates. Besides, sodium/proton antiporter operon, osmoprotectant/K+ regulator, and osmoprotectants synthesis operon may function as the main drivers of adapting to the ammonia stress. Moreover, energy from substrate-level phosphorylation and multiple energy-converting hydrogenases (e.g. Ech and Eha) could aid methanogens to balance the energy request for anabolic activities, contribute to thriving when exposed to high ammonia levels.