Dynamics and environmental importance of anaerobic ammonium oxidation (anammox) bacteria in urban river networks

Anaerobic ammonium oxidation (anammox) is recognized as an important bioprocess for nitrogen removal, yet little is known about the associated microbial communities in urban river networks which are intensively disturbed by human activity. In the present study, we investigated the community composition and abundance of anammox bacteria in the urban river network of Shanghai, and explored their potential correlations with nitrogen removal activities and the environmental parameters. High biodiversity of anammox bacteria was detected in the sediment of urban river networks, including Candidatus Brocadia, Scalindua, Jettenia, and Kuenenia. Anammox bacterial abundance ranged from 3.7 × 10⁶ to 3.9 × 10⁷ copies g^-1 dry sediment based on 16S rRNA gene, which was strongly correlated to the metabolic activity of anammox bacteria (P < 0.01). A strong linkage between anammox bacteria and denitrifiers was detected (P < 0.05), implying a potential metabolic interdependence between these two nitrogen-removing microbes was existed in urban river networks. Sediment ammonium (NH₄⁺) made a significant contribution to the anammox bacterial community-environment relationship, while anammox bacterial abundance related significantly with sediment total organic carbon (TOC) and silt contents (P < 0.05). However, no statistically significant correlation was observed between cell-specific anammox rate and the measured environmental factors (P > 0.05). In general, the community composition and abundance of anammox bacteria in different hierarchies of the river network was homogeneous, without significant spatial variations (P > 0.05). These results provided an opportunity to further understand the microbial mechanism of nitrogen removal bioprocesses in urban river networks.