Cell-associated viral community composition and its functional potential in a dimictic lake on the Canadian shield

The Turkey Lake Watershed (TLW), located in Northern Ontario, forms a cascading lake system that drains into Lake Superior. Historically, the TLW has served as a key research site for studies on acid rain and climate change. Despite its long-standing ecological importance, investigations into its microbial communities remain limited, and to date, no studies have explicitly examined the viral component of this watershed. Viruses have been frequently implicated in nutrient cycling in aquatic environments and strongly influence their microbial hosts. Therefore, viral ecology offers a powerful way to extend the environmental legacy of the TLW by identifying the biological mechanisms through which long-term changes in acid deposition, climate, hydrology, carbon chemistry, and forest disturbance propagate through microbial food webs. First steps can be a preliminary view into the type of viruses that are present, and information on which microbial hosts they may be infecting. We conducted a seasonal metagenomic survey of Big Turkey Lake (BTL)—one of the primary lakes within the TLW—from summer 2018 to winter 2020. Our study characterized the diversity and composition of cell-associated viral communities, predicted potential host relationships, and identified auxiliary metabolic genes (AMGs) to better understand the functional roles of these viruses. The results revealed a dynamic viral community that varied across seasons. Most viral contigs were classified as Caudoviricetes , while members of Phycodnaviridae emerged as important non-bacteriophage contributors to the viral assemblage. We reconstructed six draft viral metagenome-assembled genomes (vMAGs), ranging in size from 11 to 45 kbp, all identified as Caudoviricetes, with two being potential temperate phages and a third containing ribosomal genes. Notably, AMGs associated with lipid metabolism were detected exclusively in winter, suggesting a potential season- or niche-specific role for these genes in BTL. AMGs related to phosphorus acquisition were present in all samples, suggesting a potential coupling between transport dynamics of dissolved organic matter and phosphorus previously described in the TLW, and the host-virus dynamics described here. Together, these findings provide the first insight into the viral ecology of the TLW and establish a foundation for future studies investigating the roles of viruses in shaping the microbial dynamics in this important habitat.