The potential rate and microbial communities of dissimilatory nitrate reduction to ammonium in Pearl River Estuary

Abstract

Since nitrogen-related eutrophication has become a severe problem in the Pearl River Delta area in China, it is crucial to have a deep understanding of the nitrogen cycle. This study investigated the existence of dissimilatory nitrate reduction to ammonium (DNRA) in sediments of the Pearl River Estuary using the 15N isotope paring method with continuous-flow systems. The results showed that the maximum was 389.7 nmol/g in 216 h, while the maximum DNRA rate of 4.68 nmol/(g wet sediment h) occurred in 120 hours. The principal components analysis (PCA) based on community composition at the genus level was performed by the nrfA sequences distributed in the nine sites covering a salinity range of 25.3 - 30.1%º, and forming four distinct clusters. There was no significant relationship between the potential DNRA rates in the spatial distribution and salinity, but the highest potential DNRA rate occurred near the sewage discharge in the western coastal area. High contents of nrfA gene fragments were found at the same site, with values of 1159715 copies/g wet sediment, while very low contents of nrfA were found at other sites. Based on the nrfA gene pyrosequencing, Enterobacteriaceae accounts for 89.9 - 99.0% of the classified sequences.