Virus-prokaryote interactions assist pollutant removal in constructed wetlands

As a biotechnological application widely used in over 50 countries, constructed wetlands (CWs) harbor enormous viruses that can significantly affect the pollutant removal. However, the assembly and viral-host dynamics in CWs remains poorly explored. Here, two pilot scale CWs were built to investigate the viral community under different hydraulic loading rates (HLRs) using metagenomics analysis. 15,097 viral sequences were recovered from the CWs, of which approximately 30% were unknown family. Gene-sharing networks further demonstrated that the CWs were unexplored viruses pools. Based on the results of diversity, niche breadth, composition and network, HLR regulated the assembly of viral community in the CWs. Strong virus-host dynamics were observed suggesting that viruses can influence the pollutant removal in the CWs. Viruses can directly infect functional prokaryotes, such as sulfur cycling bacteria, ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA), and thus influence the nitrogen removal. In addition, viruses offered auxiliary metabolic genes (AMGs) homologous to host genes associated with sulfur and nitrogen cycling indirectly assist the nitrogen removal, with contributions ranging from 4.6% to 33.1%. Our findings advance the understanding of roles of viruses on pollutant removal in CWs, and provide a reference for design of the viral regulation strategy in wastewater treatment.