Community Structure And Denitrification Activity Of Denitrifying And Anammox Bacteria In The Estuary Offshore

Since the industrial revolution,the amount of the reactive nitrogen produced by human activities has exceeded that of the natural nitrogen fixation.The excessive reactive nitrogen has caused serious ecological and environmental problems in estuaries and coastal areas.Thus,the microbial geochemical cycle of nitrogen in coastal areas become a research hotspot.Denitrification is the most important microbial pathway for nitrogen removal and plays an important role in reducing the eutrophication of nearshore waters.Additionally,anammox is another process of nitrogen removal and plays an important role in different habitats.At the same time,the process of denitrification is accompanied by the production of intermediate nitrous oxide(N₂O),which is an important source of N₂O emissions in the coastal hydrological environment.Therefore,the process of microbial nitrogen removal in estuarine and coastal areas is closely related to environmental pollution and climate problems,and it is of great significance to study the diversity and community composition of denitrification and anammox microorganisms in estuarine coastal areas,as well as the mechanism of nitrogen removal.In this study,Jiaozhou Bay(JZB),the sandy subterranean estuary(STE)and the South China Sea(SCS)were selected as the study areas.Using the methods combining ¹⁵N isotope tracer with molecular biology,the diversity,ecological distribution and the mechanism of nitrogen removal of denitrification microorganisms in different habitats were investigated.The main conclusions of this study are listed as following:(1)The activity,abundance and community composition of nir S-type denitrifier in the surface sediments of Jiaozhou Bay,Qingdao,Shandong Province were analyzed.The results showed that denitrification was the main pathway of nitrogen removal in the sediments of Jiaozhou Bay,accounting for 81.45-99.93%of the total N₂ production,and the estimated nitrogen removal flux was 5.66×10⁴ T Ny^-1,which played an important role in mitigating eutrophication of the bay water.The denitrifying bacteria in the sediments of Jiaozhou Bay were divided into seven clusters,all belonging to the Proteobacteria.Two of the clusters were affiliated to Thiothrix and Woeseia,respectively.The other clusters were similar to the denitrifying bacteria in the sediments of bay and estuary.In addition,due to the influence of environmental conditions,the community distribution of denitrifying bacteria in sediments inside and outside the bay was significantly different.(2)There was high diversity of anammox bacteria in the SCS.In addition to the marine genus Ca.Scalindua,Ca.Brocadia and Unclassified were also detected.The relative abundance of Ca.Brocadia was 78.35%,which was the dominant genus of anammox bacteria in the SCS.In addition,the diversity of anammox bacteria was similar to the distribution pattern of the concentration of particulate organic matter.Based on the above results and previous studies,two survival strategies of anammox bacteria in aerobic marine water were proposed.One strategy is attaching to particles and using anaerobic anammox metabolism to produce energy,and the other strategy is free-living and using aerobic metabolism to produce energy.Furthermore,anammox microbes could improve their viability by switching their metabolic pathways between anaerobic and aerobic conditions.(3)The concentration of dissolved oxygen and NO₃^-in the underground water of Houmen subterranean estuary is low(DO<0.7 mg L^-1 and NO₃^-<10?mol L^-1),and there is an obvious intersection process between seawater and groundwater.Denitrification was the dominant pathway of nitrogen removal in the sediment column.At the same time,an active nitrogen removal process was detected at the interface of seawater and groundwater,and the abundance of denitrification and anammox bacteria was also relatively high.The diversity of nir S-type denitrifier was higher than nos Z?-type denitrifying bacteria.The dominant genus of anammox bacteria was Ca.Kunenenia(42.07%)and Ca.Scalindua and Unclaaified accounted for 17.98%and 39.95%,respectively.Because of the homogeneous physical and chemical conditions in the subterranean estuary,the distribution of denitrifying microorganisms was uniform.The concentration of?N₂O in the underground water of Houmen subterranean estuary is 13.50-31.83 nmol L^-1,which is an important source of N₂O release in the intertidal zones.In total,microbial denitrification contributed significantly to the reduction of eutrophication in JZB.The activities and diversity of denitrifying microorganisms in subterranean estuary are lower than those in eutrophic bay sediments,and the community structure is different,indicating that the functions of denitrifying bacteria are different in different habitats.The intersection of brine and fresh water in underground estuary can effectively promote microbial denitrification,and the denitrification is accompanied by the release process of N₂O,which is the source of N₂O.In addition,this study is the first to identify the dominance of the Ca.Brocadia genus of anammox bacteria in the marine ecosystem.The survival strategies of anammox bacteria in aerobic environment are also proposed,which provide a new idea for the removal of nitrogen-containing wastewater by anammox process.