Diversity and distribution of iamoA/i-type nitrifying and inirS/i-type denitrifying microbial communities in the Yangtze River estuary

摘要

pstrongAbstract./strong Coupled nitrificationa??denitrification plays a critical role in the removal of excess nitrogen, which is chiefly caused by humans, to mitigate estuary and coastal eutrophication. Despite its obvious importance, limited information about the relationships between nitrifying and denitrifying microbial communities in estuaries, and their controlling factors have been documented. We investigated the nitrifying and denitrifying microbial communities in the estuary of turbid subtropical Yangtze River (YRE), the largest river in Asia, by analyzing the ammonia monooxygenase gene iamoA/i, including archaeal and bacterial iamoA/i, and the dissimilatory nitrite reductase gene inirS/i using clone libraries and quantitative PCR (qPCR). The diversity indices and rarefaction analysis revealed a quite low diversity for both i?2/i-proteobacterial and archaeal iamoA/i genes, but qPCR data showed significantly higher iamoA/i gene copy numbers for archaea than i?2/i-proteobacteria. Compared with the iamoA/i gene, a significantly higher level of diversity but lower gene copy numbers were found for the inirS/i gene. Nitrification and denitrification rates based on sup15/supN incubation experiments supported gene abundance data as denitrification rates were below detection limit, suggesting lower denitrification than nitrification potential. In general, the abundances of the iamoA/i and inirS/i genes were significantly higher in the bottom samples than the surface ones, and in the high-turbidity river mouth, were significantly higher in the particle-associated ( 3 ??m) than the free-living (0.2 ~ 3 ??m) communities. Notably, positive correlations between the iamoA/i and inirS/i gene abundances suggested potential gene-based coupling between nitrification and denitrification, especially for the particle-associated assemblages. Statistical analysis of correlations between the community structure, gene abundances and environmental variables further revealed that dissolved oxygen and total suspended material might be the key factors controlling community spatial structure and regulating nitrification and denitrification potentials in the YRE ecosystem./p.