Unveiling the biodiversity of large DNA viruses in intertidal mudflats via metagenomics.

Large DNA viruses (LDVs) are unique members of the Earth's virosphere, remarkable for their extra-large genome sizes and broad metabolic potential. However, our knowledge of this viral group remains very limited, particularly in complex dynamic habitats. In this study, 237 metagenome-assembled LDV genomes are comprehensively recovered from intertidal mudflats using multiple sampling and sequencing strategies totaling 5.3 TB data. A phylogenetically distinct subgroup within Imitervirales is identified, showing broad associations with multiple eukaryotic lineages. Certain LDV populations can persist locally and exhibit significant genomic variations potentially driven by dynamic intertides. Ecological patterns are observed at both community and genetic levels, with giant viruses showing steeper community turnover but weaker nucleotide diversity variations than large phages. Moreover, LDVs exhibit similar macroecological patterns to their potential hosts, which substantially shape LDV community assembly. The intertidal LDVs encode diverse functional genes, most of which remain uncharacterized, with a 27.32% improvement for unknown phage genes using a protein language model. Although giant viruses and large phages share comparable functional gene composition, they exhibit distinct preferences for specific metabolic pathways, especially those associated with carbon and nitrogen cycling. This study broadens our understanding of the biodiversity and ecology of LDVs in the understudied intertidal ecosystems.