Segregation of Microbial Populations and Activities in the Biofilm and Suspended Phases of a Completely Autotrophic Nitrogen-Removal over Nitrite (CANON) Bioreactor

Abstract

Completely Autotrophic Nitrogen-removal Over Nitrite (CANON) moving bed biofilm reactor (MBBR) is a biofilm-based nitrogen removal system where both nitritation (ammonia oxidation to nitrite) and anaerobic ammonium oxidation (anammox) reactions occur in a single reactor under oxygen-controlled conditions. In CANON MBBR systems, the syntrophy of aerobic and anaerobic ammoniumoxidizing bacteria (AOB and AMX, respectively) is necessary to achieve stable process operation. Herein, we evaluated the spatial and temporal population and activity dynamics and niche segregation of AOB and AMX in the suspension and biofilm phases of a CANON-MBBR system. Our results demonstrated a major shift of AMX from Candidatus "Brocadia" to Candidatus "Kuenenia" during progressive reactor operation enrichment possibly due to differences in substrate affinity among these AMX guilds. In parallel, a specific differentiation in microbial N-conversion was also measured via relative expression of functional genes. Essentially, AOB activities were dominant in suspension, as inferred from the expression of ammonia monooxygenase subunit A (amoA) and AMX activities were dominant in biofilm, as inferred from the expression of hydrazine oxidase (hzo). Based on these results, it is suggested that the configuration and operating conditions in CANON MBBR systems support a systematic niche segregation of AOB and AMX ecology and activity within the biofilm and suspension phases therein.