Research On Community Structure Of Ammonia-oxidizing Microorganisms In The Biofilm Attached Bionic Plants And Its Responses To Environmental Factor

Nitrification, the microbial oxidation of ammonia to nitrate via nitrite, which is the first and rate-limiting step, plays a critical biogeochemical role in both individual ecosystems and the global nitrogen cycle. Previously, this process has long been thought to be performed exclusively by ammonia-oxidizing bacteria (AOB), only certain groups within the Beta-and Gammaproteobacteria. However, metagenomic analysis of archaea and the isolation of thaumarchaeum Nitrosopumilus maritimus, Nitrosocaldus yellowstonii and Nitrososphaera viennensis have proved the existence of ammonia-oxidizing archaea (AOA) as well as important role of them in the nitrification process. In this study, we simultaneously investigated the abundance, diversity, and community structure of AOA and AOB in (i) the water column contaminated with ammonia-nitrogen and low dissolved oxygen along the urban river in different seasons;(ii) the biofilm attached bionic plants collected from the urban river in different seasons;(iii) the bionic plants collected from the Jinshan lake which was incubated at different temperatures, pH and ammonium for up to8weeks, respectively. Relationships between the abundance and diversity of AOA and AOB, and physicochemical parameters were also explored. The results showed:(1) The water under the manual control is not suitable habitat for AOA and AOB. In wet season, a lot of water enters the Guyun River basin, and it may contribute significantly to the transport of AOA and AOB into water column. The growth rates of the ammonia-oxidizing microorganisms increased during the early dry season. However, the reduced water disturbance resulte the ammonia-oxidizing microorganisms gradually settling in the bottom of the lake or river. Quantitative studies indicated that AOB were more abundant than AOA in this environment with high ammonia concentrations. It indicated that AOB seemed to play a more important role for the nitrification process than AOA in this environment. Phylogenetic analysis showed that the Nitrosopumilus cluster was the dominated AOA group in wet season, and the Nitrososphaera cluster was the dominated AOA group in dry season. For AOB, the Nitrosomonas lineage represent a widespread AOB sequence type, and dominated in this environment. In addition, the temperature and ammonium was the key factor in controlling the abundance and community structure of AOA and AOB in this environment.(2) Physicochemical parameters of the bionic plant showed closely related to the water environment of the sample site, with significant seasonal and geographical features. The bionic plant constitutes an ideal habitat for AOA and AOB. Quantitative studies indicated that the abundance of AOA and AOB in bionic plant were higher than water column1-2orders of magnitude. Among the8samples, there were five with higher abundance of AOA than AOB, although bionic plant itself as well as the surrounding water environment with high ammonia concentrations. Phylogenetic analysis showed that the Nitrosopumilus cluster was the dominated AOA group in MXN1and MXG6, while the Nitrososphaera cluster was the dominated AOA group in the other six samples. Among the8bacterial amoA gene clone libraries, the Nitrosomonas lineage was dominated. In addition, the nitrite and ammonium was the key factor in controlling the abundance and community structure of AOA and AOB in the bionic plant.(3) Incubation at different temperatures, pH and ammonium for up to8weeks, respectively, the result showed a large variation in the abundance of AOA as well as AOB in all of the samples. However, the microbial community composition of AOA changed slightly. It seems that AOA populations may have a strong ability to adapt the change of environment. On the other hand, a significant changes was observed in the microbial community composition of AOB. These results indicated that AOA and AOB have different metabolic mechanisms and ecological niches.This work could enhance our understanding of the roles of ammonia-oxidizing microorganisms in the Guyun River basin, and provide reliable data and theoretical basis for ecological remediation of urban river using bionic plants.