Increased Replication Rates of Dissimilatory Nitrogen-Reducing Bacteria Leads to Decreased Anammox Reactor Performance

Anaerobic ammonium oxidation (anammox) is a biological process employed to remove reactive nitrogen from wastewater. While a substantial body of literature describes the performance of anammox bioreactors under various operational conditions and perturbations, few studies have resolved the metabolic roles of community members. Here, we use metagenomics to study the microbial community within a laboratory-scale anammox bioreactor from inoculation, through performance destabilizations, to stable steady-state. Metabolic analyses reveal that dissimilatory nitrogen reduction to ammonium (DNRA) is the primary nitrogen removal pathway that competes with anammox in the bioreactor. Increased replication rates of bacteria capable of DNRA leads to out-competition of annamox bacteria, which is the key source of fixed carbon, and the loss of reactor performance. Ultimately, our findings underline the importance of metabolic interdependencies related to carbon and nitrogen-cycling within anammox bioreactors and highlight the potentially detrimental effects of bacteria that are otherwise considered to be core community members.