Abundance And Diversity Of 16S RRNA And AmoA Genes In Sediments Of Liaohe Estuary

In recent years,the global overproduction of active nitrogen from human sources has destroyed estuaries and marine coastal ecosystems,resulting in some loss of ecological functions,biodiversity loss,eutrophication of water bodies and frequent occurrence of harmful red tides.Nitrogen is one of the important biogenic elements in the biogeochemical cycle.It is one of the elements that limit the biological productivity of estuarine ecosystems.The biogeochemical cycles of nitrogen in the estuaries affect the ainability of estuary ecosystem productivity and even the global environmental changes.Nitrification,as the central link between nitrogen fixation and denitrification,can mitigate the toxicity of ammonia nitrogen in estuarine and coastal environments and is an important process of global nitrogen cycle.Ammonia oxidation is the first step and the rate-limiting step of nitrification.It is the oxidation of ammonia?NH₄⁺?to nitrite?NO₂^-?,the main microorganisms involved in this process are ammonia oxidative archaea?AOA?and ammonia-oxidizing bacteria?AOB?,which is an important bioremediation process in nitrogen-rich environment and has important ecological significance.In July 2016,experimental samples were collected from Liaohe River estuary,and the abundance and community structure of archaea,bacteria and ammonia oxidizing microorganisms in Liaohe Estuary were studied by means of microbial molecular biology.The main research contents and results are as follows:1?Illumina Miseq sequencing technology for archaeal and bacterial 16S rRNA gene sequence analysis.The results showed that the bacterial diversity in surface sediments of Liaohe River was higher than that of archaea,and the diversity of bacteria and archaea in nearshore was higher than that of far shore.The major archaeal communities were Thaumarchaeota?72.73%?and Euryarchaeota?25.05%?.Proteobacteria?61.94%?were the dominant bacteria in the estuarine community,followed by Bacteroidetes?11.21%?and Acidobacteria?5.59%?.2?Real-time fluorescent quantitative PCR was used to determine the abundance of archaral,bacterial 16S rRNA and ammonoxagenase?amoA?gene.The results showed that the16S rRNA gene abundance ranged from 1.05�10⁸ to 1.31�10⁹ copies/g.The abundance of16S rRNA gene in bacteria varied from 3.05�10¹⁰ to 1.37�10¹² copies/g,Out of 2 to 3orders of magnitude.The abundance of AOA amoA gene ranged from 3.10�10⁶ to 2.85�10⁷copies/g.The abundance of AOB amoA gene varied from 6.59�10⁵ to 1.20�10⁷ copies/g,and the abundance of AOA in all stations was higher than that of AOB.3?The amoA gene cloning library was used to study the community structure of AOA and AOB and its influence on environmental factors.The results of phylogenetic analysis showed that the amoA gene sequences of archaea clustered into four different clusters?Cluster?^??.The major taxa are Nitrosopumilus and Nitrosophaera,and Nitrosopumilus is the largest taxa.Except for stations 1 and 5,all other stations are sequenced in this cluster.The bacterial amoA gene sequences were clustered into two different clusters?Cluster A and Cluster B?.The first cluster is Nitrosomonas and contains 9 sequences.The second cluster consists mainly of estuarine sediments and wetland soils.4?Canonical correspondence analysis?CCA?of community structure with environmental factors showed that the main water environmental factors affecting the distribution of AOA in surface sediments were salinity,pH,NH₄⁺,and conductivity,but no significant effect of water environment on AOB communities in the Liaohe Estuary sediments was found.Sand,silt,and total phosphorus?TP?have significant effects on AOA community structure in sediment environmental factors,and sand and silt content have significant effects on AOB community structure.Thus,under different environmental conditions microbial community structure exists spatial heterogeneity,different microorganisms respond to the same environmental conditions are also different.In this study,the surface sediments of the Liaohe estuary were used as the research object,and the ammoxidation process was studied from the perspective of microbial molecular ecology to reveal the abundance and community structure characteristics of archaea,bacteria,and ammonia-oxidizing microorganisms in the Liaohe estuary sediments.The results of the study will help deepen the understanding of microbial participation in biogeochemical cycles in the estuary area.