WWTP effluents influence prokaryotic viral diversity and interaction with hosts: Regulating the virus-mediated...

As an important water replenishment measure for urban rivers, the input of wastewater treatment plant (WWTP) effluents can change both the nutrient loading and the microbial community diversity of receiving rivers. However, our knowledge of the characteristics of viral communities and virus-mediated nitrogen-cycling processes in WWTP effluents-receiving rivers remains very limited. In this study, the prokaryotic virus, host and non-host communities in sediments were detected via metagenome and virome methods, to explore the variation characteristics of viral communities, interactions with hosts and virus-mediated nitrogen-cycling processes along the upper reference reach (UR), middle receiving reach (MR) and lower recovery reach (LR) of a typical WWTP effluents-receiving river. The results showed that compared to the non-hosts, viruses and hosts were much more sensitive to the influence of WWTP effluents. Among the three reaches, viruses and hosts showed more obvious spatial variability in community diversity and structures than those of non-hosts. Compared to UR, viruses in MR displayed the highest community diversity and virus-to-host abundance ratio, while viruses in LR maintained the high abundance ratio. Co-occurrence network analysis indicated the more important central roles of viruses than those of prokaryotes in bridging species or groups within the virus-host-prokaryote communities, especially in MR and LR. Functional gene analyses revealed that viral communities might potentially regulate nitrogen cycles in MR and LR via two pathways: directly carrying more abundant nitrogen-related auxiliary metabolic genes (N-vAMGs) and indirectly regulating hosts involved in nitrogen transformations (N-hosts) via enriched viruses, which showed strong responses to nitrogen loadings (TN and NO₃^--N) in rivers. Both N-vAMGs and virus-enrichment N-hosts, dominantly involved in denitrification, dissimilatory nitrate reduction to ammonium, and organic degradation and synthesis processes, significantly increased in MR and LR, which highlighted a long-term regulation potential of viral communities to WWTP effluents-receiving rivers. Together, these findings provided a new insight into the nonnegligible ecological role of viruses in influencing biogeochemical cycles in WWTP effluents-receiving urban rivers.