Discovery of novel metabolic pathways and regulatory mechanisms of ammonia-oxidizing bacteria in organic materials stabilization

Background Ammonia-oxidizing bacteria (AOB) play a crucial role in the microbiome of the global nitrogen cycle. Yet, their regulatory functions in the metabolic pathways involved in organic material stabilization (OMS) are not fully understood. We employed metabolomics, microbiomics, and molecular biology techniques to investigate for the first time the metabolic changes and regulatory mechanisms of OMS in a cow manure and straw biostabilization system inoculated with a novel exogenous consortium-AOB (C-AOB). 
Results C-AOB engaged in nitrogen metabolism during the thermophilic phase and participated in carbon metabolism during the stabilization phase of OMS. Glutamate was a key metabolite bridging the carbon and nitrogen metabolic networks, which increased during humic formation. C-AOB inoculation stimulated NO2- production, enhanced glycolysis and the tricarboxylic acid cycle, thereby facilitating glutamate conversion and contributing to humic formation. Additionally, NO2- served as a nitrogen source for microbial proliferation, thus enhancing microbial community activity and stability. The observed increase in the abundance of amoA, that encodes ammonia monooxygenase, indicates a close association between C-AOB inoculation and increased glutamate content. 
Conclusions The key metabolites, enzymes, and genes, particularly those associated with glutamate, played a role in regulating OMS by C-AOB. These findings underscore the regulatory roles of AOB in the metabolic pathways involved in OMS, which is of global concern.