Metagenomic insights into the mechanism for the rapid enrichment and high stability of Candidatus Brocadia facilitated by ferric ion

The rapid enrichment of anammox bacteria and its fragile resistance to environment changes are the critical problems facing of anammox processes. As an abundant component in anammox bacteria, iron has been proved to promote the activity and growth of anammox bacteria in the mature anammox systems, but the functional and metabolic profiles in Fe(III) enhanced emerging anammox systems have not been evaluated. Results indicated that the relative abundance of functional genes involved in oxidative phosphorylation and nitrogen metabolism, cofactors synthesis, and extracellular polymers synthesis pathways was significantly promoted in the system added with 5 mg/L Fe(III).These enhanced pathways were crucial to energy generation and nitrogen removal, cell activity and proliferation, and microbial self-defense, thereby accelerating the enrichment of anammox bacteria Candidatus Brocadia and facilitating their resistance to adverse environments.