Exploring The Active Ammonia-oxidizing Microorganisms In The Sediments Of The Shengzhong Lake By DNA-based Stable Isotope Probing Technique

The aerobic ammonia oxidation process is an important step in the nitrogen cycle,it is also the rate-limiting step of nitrification.Anaerobic ammonium oxidation is recognized as an important process in the nitrogen cycle,which use NH₄⁺and NO₂^-as substrates to produce N₂.Aerobic and anaerobic ammonia oxidizing microorganisms are widely distributed in the environment.However,the ammonia oxidizing microorganism groups in different environments are significantly different.As an important wetland ecosystem,the active ammonia-oxidizing microorganisms in the sediments of lakes still needs to be clarified.Therefore,we chose"the largest man-made freshwater lake in western China"Shengzhong Lake as the research object.The active aerobic and anaerobic ammonia oxidizing microorganisms in lake sediments were explored using DNA-based stable isotope probing(DNA-SIP)combined with high-throughput sequencing analysis.Meanwhile,the impact of temperature on the active ammonia oxidizing microorganisms in the sediments was also determined.The main research content and results of the thesis are as follows:1.The nitrification activity and active ammonia oxidizing microorganisms in lake sediments under different temperature conditions were determined.The experiment set two temperatures,10?(in-situ ambient temperature)and 25?(warming temperature),both incubation under aerobic conditions.The results are as follows:(1)The nitrification rate of lake sediments was significantly stimulated at 25?,compared with that at 10?;(2)The results from DNA-SIP experiment showed that ammonia-oxidizing bacteria(AOB),ammonia-oxidizing archaea(AOA),and anaerobic ammonia oxidizing bacteria(Anammox bacteria)were labeled by ¹³C under the two temperature conditions;The complete ammonia oxidizer(Comammox)was only labeled at 10?;The labeling degree of AOB,AOA and Anammox bacteria at 25? were all markedly higher than those at 10?.(3)Increase temperature could alter the dominant AOB community in the sediments.The dominant AOB was affiliated with Nitrosomonas at 10?,whereas the dominant AOB was belonging to Nitrosospira at 25?;(4)The dominant Anammox bacteria was not altered by the increased temperature treatment.The dominant Anammox was Candidatus Brocadia under both conditions.(5)The domiant AOA was Nitrosopumilus which was belonging to Group 1.1a;(6)The domiant Comammox was belonging to MBR Nitrospira bin 1 at 10?.2.The nitrification activity and active ammonia oxidizing microorganisms in lake sediments under anaerobic conditions were determined.The experiment was set at 25?and cultivated under anaerobic conditions.The results are as follows:(1)The nitrification rate of lake sediments was significantly stimulated at aerobic conditions,compared with that at anaerobic conditions;(2)The results from DNA-SIP experiment showed that ammonia-oxidizing bacteria(AOB),anaerobic ammonia oxidizing bacteria(Anammox bacteria),and Complete ammonia oxidizer(Comammox)were labeled by¹³C under the anaerobic conditions;(3)The dominant AOB was affiliated with Nitrosospira at anaerobic conditions;The dominant Anammox bacteria was affiliated with Candidatus Anammoximicrobiu;The dominant Comammox was affiliated with Candidatus Nitrospira inopinata.Among them,the dominated Anammox bacteria and Comammox under the aerobic environment were significantly different from the anaerobic environment.In summary,Aerobic and anaerobic ammonia oxidizing microorganisms can both promote the ammonia oxidation process in both aerobic and anaerobic environments.Aerobic and anaerobic ammonia oxidizing microorganisms can both promote the ammonia oxidation process in both aerobic and anaerobic environments.The environment factors,such as changes in temperature,aerobic or anaerobic environmental conditions,will lead to the differentiation of active ammonia-oxidizing microbial communities in lake sediments.The research has important reference value for understanding the ecological functions of ammonia oxidizing microorganisms in different niches.Under the background of global climate change,it provides valuable data for the research on the evolution direction of ammonia oxidation in freshwater lake sediments ecosystem.