Diversity Of Ammonia Oxidizing Microorganisms And Nitrification In Liaohe Estuary Sediments

Nitrification is the central link in the biogeochemical cycle of nitrogen, and ammonia oxidation is the first step in nitrification, and it is also the rate-limiting step. Ammonia oxidizing microorganisms play an important role in the process of ammonia oxidation in the area of the estuary.Sediment samples were collected from Liaohe Estuary in May 2014, and ammonia oxidizing microorganisms of the samples were studied. In this study, real-time quantitative PCR and Miseq high-throughput sequencing technology were used to determine the abundance and diversity of ammonia oxidizing bacteria and the diversity of ammonia oxidizing archaea using the amoA gene as a molecular marker in the Liaohe Estuary sediments. In addition, the sediment slurries incubation experiment was utilized to examine the potential nitrification rate in sediments. The results were as follows:1、The results of potential nitrification rate showed that the nitrification rates in the upper sediment were higher than that of the lower layer, and the nitrification rates ranged from 0.4 to 336.8 nmol N g-1 day-1. Besides, nitrification rate values showed a rising trend along the estuary to the sea, which illustrated the nitrification potential in high-salinity environment was higher than that of the low salinity environment in estuary.2、Real time quantitative PCR experiments showed that the the amoA gene abundance of ammonia oxidizing bacteria in the sediment was in the range of 8.54× 104 to 5.85× 106 copies g-1. The amoA gene abundance in the upper layer(0-2 cm) samples was higher than that in the lower layer(2-4cm) sample for each station, showing a rising trend along the estuary to the coastal area. This result was consistent with the potential nitrification rate in the estuarine sediments, which indicated that the ammonia oxidizing bacteria might play an important role in the process of nitrification in the Liaohe Estuary.3、The richness index of ammonia oxidizing bacteria showed a decreasing trend along the estuary to the sea. The changes of evenness index of ammonia oxidizing bacteria were roughly consistent with the changes of richness index.Phylogenetic analysis of ammonia oxidizing bacteria illustrated that amoA gene sequences of ammonia oxidizing bacteria obtained belonged to Nitrosomonas and Nitrosospira genus. The majority of OTU sequences were affiliated to Nitrosomonas marina, Nitrosomonas aestuarii and Nitrosomonas-like lineage, and the rest of OTU sequences belonged to Nitrosospira lineage. Nitrosomonas genus dominanted in the total OTU, and due to ammonia oxidizing bacteria were mainly comprised by Nitrosomonas genera in the stations where there had high nitrification potential. Thus, Nitrosomonas genus of ammonia oxidizing bacteria might play an important role in the nitrification process of Liaohe Estuary.4、Phylogenetic analysis of ammonia oxidizing archaea showed that sequences of ammonia oxidizing archaea mainly belonged to Nitrososphaera,Candidatus and Nitrosopumilus genus. Candidatus genus of ammonia oxidizing archaea have a strong ability to adapt to high-salinity environment, and may play an important role in ammonia oxidation process in marine environment.Here, ammonia oxidation process in Liaohe estuarine sediments was studied from the perspective of molecular microbial ecology, in order to reveal the diversity characteristics of ammonia oxidizing microorganisms in the sediments environment of Liaohe Estuary. The results of the study will be helpful to enhance the understanding of the ammonia oxidizing microorganisms in the estuary area.