Metagenomic insights into comparative study of nitrogen metabolic potential and microbial community between primitive and urban river sediments

As a result of anthropogenic pollution, the nitrogen nutrients load in urban rivers has increased, potentially raising the risk of river eutrophication. Here, we studied how anthropogenic impacts alter nitrogen metabolism in river sediments by comparing the metagenomic function of microbial communities between relatively primitive and human-disturbed sediments. The contents of organic matter (OM), total nitrogen (TN), NO3- - N and NO2- -N were higher in primitive site than in polluted sites, which might be due to vegetation density, sediment type, hydrology, etc. Whereas, NH4+- N content was higher in midstream and downstream, indicating that nitrogen loading increased in the anthropogenic regions and subsequently leading higher NH4+- N. Hierarchical cluster analyses revealed significant changes in the community structure and functional potential between the primitive and human-affected sites. Metagenomic analysis demonstrated that Demequina, Streptomyces, Rubrobacter and Dechloromonas were the predominant denitrifiers. Ardenticatena and Dechloromonas species were the most important contributors to dissimilatory nitrate reduction. Furthermore, anthropogenic pollution significantly increased their abundance, and resulting in a decrease in NO3-, NO2- -N and an increase in NH4+- N contents. Additionally, the SOX metabolism of Dechloromonas and Sulfuritalea may involve in the sulfurdependent autotrophic denitrification process by coupling the conversion of thiosulfate to sulfate with the reduction of NO3- -N to N2. From pristine to anthropogenic pollution sediments, the major nitrifying bacteria harboring Hao transitioned from Nitrospira to Nitrosomonas. This study sheds light on the consequences of anthropogenic activities on nitrogen metabolism in river sediments, allowing for better management of nitrogen pollution and eutrophication in river.