Comparison of the Microbial Community Structure in Nitrifying Processes Operating with Different Dissolved Oxygen Concentrations

Abstract

High-throughput sequencing was applied to analyze the microbial community structure of nitrifying reactors operated with different dissolved oxygen (DO) levels. Results showed that the nitrifying reactor (RL) run with low DO (0.2-0.3 mg·L-1) exhibited greater microbial richness and diversity than the reactor run under the high DO condition[RH, DO=(2.0±0.1) mg·L-1]. In contrast, the microbial community in RH was more highly functionally organized than that in RL. Although the communities in RH and RL shared over 85% of the total sampled genetic information, the relative abundance of some individual species varied between the different DO conditions. Members of the Proteobacteria phylum, which accounted for 80.7% of the total microbes in RH, were highly enriched, and the relative abundance of Nitrosomonas reached to 65.1%. However, the microbial community in RL was dominated by Proteobacteria (43.8%), Firmicutes (20.0%), and Bacteroidetes (15.1%). In addition, a large fraction of bacteria possessing hydrolyzation and fermentation functions under anaerobic or anoxic conditions were also present in RL including Lactococcus, Anaerolineaceae, and Rhodocyclaceae. As known ammonium-oxidizing bacteria, Nitrosomonas oligotropha and Nitrosomonas europaea were enriched in the RH and RL, respectively, while Nitrospira defluvii, being a nitrite-oxidizing bacteria, dominated both reactors. Rather than DO, ammonia and nitrite availability should be key factors in the selective enrichment of these nitrifiers.