Metagenomic analysis of viral communities in the polluted Varuna River reveals site-specific diversity patterns associated with environmental aspects.

Abstract

Varuna River, which is native to Varanasi, is of great importance as a water reservoir for the people and is contaminated with heavy pollutants due to urbanization. In this study, four sites (VR1, VR2, VR3, and VR4) of Varuna River water were sampled to assess the viral diversity. The metagenomics approach was used to study the viral diversity and functional analysis, suggesting the overall quality of the water at the sampled location. The analysis shows that VR1 had the most species richness (3000 species), followed by VR3 (2500), VR2 (2000), and VR4 (1500). The PCA analysis revealed distinct spatial patterns and community differentiation where VR2 and VR4 clustered while VR1 and VR3 were distant.Diversity analysis showed that Negarnaviricota dominated all samples at the phylum level. Yunchangviricetes, a non-reported virus, and Insthoviricetes were the dominant classes. Pakpunavirus was the leading genus, followed by the human pathogen Mimivirus. The highest species abundance in VR1 and VR2 was Mimivirus, Megavirus, chilensis, while VR3 and VR4 had Hpunavirus and Pseudomonas phage O4, indicating human involvement. Functional analyses of enzymatic activity and KEGG Orthology in microbial communities from VR1 to VR4 samples showed that VR4 exhibited maximal enzymatic activity, genetic flexibility, and advanced regulatory control compared to the other samples. The increased presence of transporter genes alongside signal transduction proteins and metabolic enzymes in VR4 indicates enhanced functional diversity, which aids in coping with environmental stresses. On the basis of viral species, ecological, biotechnological aspects were also interpreted. This study concluded that the Negarnaviricota plays a key role in maintaining the overall water quality and there is an urgent need for remediation of the Varuna River especially at site VR4 (25° 19' 46.7″ N 83° 02' 38.3″ E).