Abstract
Ammonia released from the degradation of protein and/or urea usually leads to suboptimal anaerobic digestion (AD) when N-rich organic waste is used. However, the insights behind the differential ammonia tolerance of anaerobic microbiomes remain an enigma. In this study, the cultivation in synthetic medium with different carbon sources (acetate, methanol, formate, and 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 NH+-N/L, whereas the other two groups (formate and acetate) only thrived at 5.25 and 4.25 g NH+-N/L, respectively. Metabolic reconstruction highlighted that 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 the AD of N-rich substrates. Besides, sodium/proton antiporter operon, osmoprotectant/K+ regulator, and osmoprotectant synthesis operon may function as the main drivers of adaptation to the ammonia stress. Moreover, energy from the substrate-level phosphorylation and multiple energy-converting hydrogenases (e.g., Ech and Eha) could aid methanogens to balance the energy request for anabolic activities and contribute to thriving when exposed to high ammonia levels.
Highlights
The amount of nitrogen-rich organic waste generated worldwide is increasing significantly because of urbanization and population growth, which is becoming a major issue for the environment.[1]
Extremely diverse communities composed of thousands of metagenome-assembled genomes (MAGs) and complex metabolic activities adapted to mixed substrate degradation were found.[30,33,34]
This study provides novel insights into ammonia-tolerant methanogenic communities grown using four different carbon sources in a synthetic basal anaerobic (BA) medium
Summary
The amount of nitrogen-rich organic waste generated worldwide is increasing significantly because of urbanization and population growth, which is becoming a major issue for the environment.[1]. Metagenomics have been recently applied to analyze the known and novel physiological, metabolic, and genetic features.[16,30] So far, most AD metagenomic studies focus on communities shaped by real feedstocks such as manure, wastewater, industrial by-products, and municipal solid waste containing various carbon sources.[31,32] extremely diverse communities composed of thousands of metagenome-assembled genomes (MAGs) and complex metabolic activities adapted to mixed substrate degradation were found.[30,33,34] These findings raise the possibility that specific interactions of ammonia-tolerant microbial members fed with single and simple carbon sources (the common precursors, i.e., acetate, formate, H2−CO2, and methanol) and their functionalities await discovery. The first look into the metabolism of the four microbiomes shaped by specific carbon sources showed how metabolic interactions occur among microbes at high ammonia levels
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