The biogeography of giant viruses and interactions with Eukaryotes across European lakes.

Advances in genomics have revealed a diversity of nucleocytoplasmic large DNA viruses (phylum Nucleocytoviricota) that infect eukaryotes, but their ecology beyond the oceans remains poorly understood. We recover 208 Nucleocytoviricota genomes, including 205 putative new species and 33 novel virus-host linkages by sampling 87 lakes spanning 30° of latitude from southern Italy to northern Norway. The relative abundance of Nucleocytoviricota nearly triples, on average, from northern to southern Europe, with functional genes related to autotrophic energy acquisition, stress responses, and cell death predominant at lower latitudes. These shifts are attributable to differences in light and resources, with Nucleocytoviricota hotspots in deep lakes with aromatic organic matter and diverse eukaryote communities. Increasing Nucleocytoviricota abundance and richness are associated with several-fold reductions in gross primary production. Our results highlight that Nucleocytoviricota are ecologically relevant in lakes and that understanding their roles will be essential for predicting aquatic food webs under environmental change.