Metagenomic analysis of DNA viruses in a wastewater treatment plant in tropical climate

Viruses have been detected in the different stages of wastewater treatment plants (WWTPs) at concentrations of 10 ⁸-10 ¹⁰ml ^-1 of virus-like particles (VLPs), 10-1000 times higher than in natural aquatic environments, suggesting that WWTPs can be considered as an important reservoir and source of viruses. This study revealed novel diversity and function with the DNA viral communities in the influent, activated sludge, anaerobic digester, and effluent of a domestic WWTP using metagenomics. WWTP was a very specific environment, with less than 5% of the >936000 metagenomic sequences obtained (∼70-119Mbp per sample) similar to sequences present in other environmental viromes. Many viruses found in the WWTP were novel, resulting in only <5-20% of the reads being phylogenetically or functionally assigned. DNA metabolism was observed as the most abundant function with DNA methylase detected at levels 4.2-fold higher than other published viromes, while carbohydrate and amino acids metabolisms were 3.7- and 4.2-fold less abundant respectively. These specific aspects of the WWTP community functions are likely due to high biomass concentration, turnover rate and microbial activity in WWTPs, and likely include mechanisms that help viruses increase their infectivity. Among ∼500 genotypes estimated in individual WWTP viromes,>82% were shared. These data suggested that VLPs of most viral types could be present between 1 and 30 days in the process before they were discharged. Viruses in WWTP and the discharged ones can have potential impacts on the functioning of the wastewater treatment system and on the dynamics of microbial community in the surrounding aquatic environments respectively.