Changes of abundance and diversity of ammonia-oxidizing archaea (AOA) and bacteria (AOB) in three nitrifying bioreactors with different ammonia concentrations

Different from ammonia-oxidizing bacteria (AOB), the influence of ammonia levels on ammonia-oxidizing archaea (AOA) in wastewater treatment systems was poorly understood. In this study, sludge contained AOA and AOB was enriched in three sequencing batch reactors (named as R1, R2, and R3) under different ammonia levels (14, 56, and 140 mg/L) using polymerase chain reaction (PCR), cloning, sequencing, and quantitative real-time PCR (qPCR) to evaluate the effect of ammonia levels on the diversity, abundance, and contribution of AOA and AOB to ammonia oxidation. Cloning results showed that there was only one dominant AOA species (Nitrososphaera cluster) in the reactors during 140-d operation. However, AOB communities varied significantly among the reactors. After 140-d enrichment, Nitrosomonas ureae cluster, the dominant AOB cluster in seed sludge, was also dominant in R1 and R2, while Nitrosomonas europaea cluster was enriched and dominated in R3. Diversity of AOB was higher than AOA under the three ammonia levels. Diversity of AOB under high ammonia concentration (in R3) was lower than that under low ammonia concentrations (in R1 and R2). QPCR results revealed that AOA abundance was almost unchanged under different ammonia levels during operational period. The ratio of AOB to AOA increased from 3.68 × 102 in seed sludge to 4.90 × 103, 1.25 × 105, and 3.77 × 105 in three reactors after 140-d running. This study suggested that AOB was much more competitive than AOA in high ammonia level environments and probably played a more important role than AOA in ammonia oxidation.