Geographical Patterns of nirS Gene Abundance and nirS-Type Denitrifying Bacterial Community Associated with Activated Sludge from Different Wastewater Treatment Plants

Denitrifying bacteria is a driver of nitrogen removal process in wastewater treatment ecosystem. However, the geographical characteristics of denitrifying bacterial communities associated with activated sludge from diverse wastewater treatment plants (WWTPs) are still unclear. Here, quantitative PCR and next-generation sequencing of the nirS gene were applied to characterize the abundance and denitrifying bacterial communities from 18 geographically distributed WWTPs. The results showed that the nirS abundance ranged from 4.6x10(2) to 2.4x10(3) copies per ng DNA, while nirS-type denitrifying bacterial populations were diverse and distinct from activated sludge communities. Among WWTPs, total nitrogen removal efficiencies varied from 25.8 to 84%, which was positively correlated with diversity indices, whereas abundance-based coverage estimator index decreased with an increase in latitude. The dominant phyla across all samples were proteobacteria, accounting for 46.23% (ranging from 17.98 to 87.07%) of the sequences. Eight of the 22 genera detected were dominant: Thauera sp., Alicycliphilus sp., and Pseudomonas sp., etc. Based on network analysis, the coexistence and interaction between dominant genera may be vital for regulating the nitrogen and carbon removal behaviors. Multivariate statistical analysis revealed that both geographic location and wastewater factors concurrently govern the distribution patterns of nirS-type denitrifying bacterial community harbored in WWTPs. Taking together, these results from the present study provide novel insights into the nirS gene abundance and nirS-type denitrifying bacterial community composition in geographically distributed WWTPs. Moreover, the knowledge gained will improve the operation and management of WWTPs for nitrogen removal.