Deep-sea viral diversity and their role in host metabolism of complex organic matter.

Viruses exert a pervasive influence on biogeochemical cycles in deep-sea ecosystems. Cold seeps and seamounts, globally distributed across the oceans and harboring diverse microbial communities, remain largely unexplored regarding their viral inhabitants and functions. By integrating metagenomic, DNA viromic, RNA viromic, and metatranscriptomic data, coupled with characterization of purified viral communities, we uncover the diversity of DNA and RNA viral communities and virus-host interactions, which vary significantly across distinct deep-sea sediment sites. These sites represent a declining cold seep, a site distant from the declining cold seep (sediment site), a nascent cold seep site, and a seamount. The viral community in the nascent cold seep displays unique characteristics, with an increased proportion of RNA viruses and temperate viruses. Viral genomic and metatranscriptomic analyses reveal viral functional genes are actively expressed, potentially enhancing host metabolism of complex organic matter. Here, our findings underscore the diversity, ecological roles, and host interactions of viral communities in different cold seeps and seamounts, suggesting the importance of viruses in deep-sea carbon cycling and microbial community structure.