Metagenomic analysis of virus diversity and relative abundance in a eutrophic freshwater harbour
Aquatic viruses have been extensively studied over the past decade, yet fundamental aspects of freshwater virus communities remain poorly described. Our goal was to characterize particle-associated virus communities seasonally and spatially in a freshwater harbour. Community DNA was extracted from water samples and sequenced on an Illumina HiSeq platform. Assembled contigs were annotated as belonging to the virus families Caudovirales, Mimiviridae, Phycodnaviridae, and virophages (Lavidaviridae), or to other groups of undefined viruses. Diverse Mimiviridae contigs were detected in the samples, but the two sites contained distinct Mimiviridae communities. Virophages were often the most abundant group, and discrete virophage taxa were remarkably stable across sites and dates despite fluctuations in Mimiviridae community composition. Caudovirales were present at low abundances in most samples, contrasting other studies of freshwater environments. Similarly, Phycodnaviridae abundances were surprisingly low in all samples despite the harbours capacity to support high algal biomass during the summer and autumn months, suggesting that Mimiviridae are the dominant algae-infecting viruses in this system. Overall, our findings provided insights into freshwater virus community assemblages by expanding the documented diversity of freshwater virus communities, highlighting the potential ecological importance of virophages, and revealing distinct communities over small spatial scales.