Community Composition Of Dissimilatory Nitrate Reduction To Ammonium (DNRA) Bacteria In Systems Of Activated Sludge And Agricultural Lands

Previous studies on the dissimilatory nitrate reduction to ammonium?DNRA?,mainly concentrated in the oceans,estuaries,shallow sediments and wetland soil.There were few studies on DNRA in the activated sludge system of municipal sewage treatment plants and typical dryland farmland soil ecosystems.DNRA and denitrification competed with the substrate NO₃^--N together.Recent studies have found that DNRA plays an important role in NO₃^--N removal.In this paper,high-throughput sequencing of functional genes nrfA and bacterial 16S rRNA in DNRA was carried out to study the bacterial community composition,bacterial diversity and their correlation with environmental factors in activated sludge and soil samples.To further explore the distribution of DNRA in different environments and provide the basis for the study of DNRA.The functional gene nrfA of DNRA bacteria was cloned from 8 activated sludge samples collected from municipal sewage treatment plants at different latitudes in China.It was found that DNRA bacteria existed in all 8 sludge samples.Further high-throughput sequencing of nrfA gene was carried out.After quality control,160,000sequences were obtained for each sample,and 11847 OTUs were divided under the condition of similarity??90%?.268 OTUs of them were selected as representative for ecological analysis.The results showed that the community structure of CQ and GZ,CC and TP,BJ-1,BJ-2 and BJ-3 were similar,and the difference of geographic environment of sample sites had a great influence on DNRA bacterial community composition in municipal wastewater treatment plants.The representative OTUs were classified and annotated to 10 phylum and 30 genus.The three genus with the highest relative abundance were Nitrospira?22.28%?,Candidatus Brocadia?13.28%?and Aneromyxobacter?13.08%?,which indicated that they were dominant in the community composition.Network analysis showed that Nitrospira played an important role in the DNRA bacterial community of municipal wastewater treatment plants.Real-time fluorescence quantitative PCR?qPCR?results showed that the proportion of DNRA functional microorganisms in activated sludge was 0.18%³.94%,lower than that of denitrifying bacteria?0.68%¹0.06%?.Further analysis of 16S rRNA high throughput sequencing showed that the relative abundance of DNRA functional microorganisms containing nrfA functional genes?5.27%?was lower than that of denitrifying microorganisms?17.15%?.The relative abundance of DNRA bacteria was mainly related to the total nitrogen and ammonia nitrogen content in influent and the properties of MLSS,VSS,TC,TN and TS in sludge.Dryland farmland soil is divided into rhizosphere and non-rhizosphere,and four typical crops.After quality control,each sample has 87,000 sequences,which are divided into 27,952 OTUs with?90%similarity.258 representative OTUs with higher abundance are selected for ecological analysis.The results of diversity analysis?OTUs level?showed that the DNRA community richness,species diversity and species evenness of 3/4 crop rhizosphere soil samples were higher than those of corresponding non-rhizosphere soil samples.Compared with the four crops,the DNRA community diversity of root soil of millet was the highest,and that of non-rhizosphere soil of maize was the lowest.The representative OTUs were classified and annotated to 6 phylum and19 genus.The three genus with the highest relative abundance were Hyalangium?29.31%?,Chthoniobacter?20.33%?and Nitrospira?13.41%?.Combined with soil physical and chemical factor analysis,the relative abundance of DNRA community was significantly correlated with NO₂^--N,TN,water content,TOM,pH and temperature.To some extent,this study revealed the distribution of DNRA bacterial community in activated sludge of sewage treatment plant and dryland farmland soil,and its correlation with environmental factors.Objective to provide an effective theoretical basis for improving nitrogen removal efficiency in sewage,improving the utilization efficiency of nitrogen fertilizer,reducing the release of greenhouse gas N₂O,reducing environmental pollution and improving the global nitrogen cycle process.