Giant virus diversity and host interactions through global metagenomics

Current knowledge about the nucleocytoplasmic large DNA viruses (NCLDV) is largely derived from viral isolates co-cultivated with protists and algae. Building on the rapidly increasing wealth of publicly available metagenome data, we reconstructed 2,074 NCLDV genomes from sampling sites spanning the globe. This led to an 11-fold increase in phylogenetic diversity and a parallel 10-fold expansion in functional diversity. Analysing 58,023 metagenomic major capsid proteins of large and giant viruses revealed global distribution patterns and underlined their cosmopolitan nature. The discovered viral genomes encoded a wide range of proteins with putative roles in photosynthesis and diverse substrate transport processes, revealing host reprogramming as a likely common strategy in the NCLDV. Furthermore, horizontal gene transfer inferences connected viral lineages to diverse eukaryotic hosts. We anticipate that the vast diversity of NCLDV revealed here on a global scale will establish giant viruses as key ecosystem players across Earth's biomes, associated with most major eukaryotic lineages.