Marine viruses discovered via metagenomics shed light on viral strategies throughout the oceans

Marine viruses are key drivers of host diversity, population dynamics and biogeochemicalcycling and contribute to the daily flux of billions of tons of organic matter. Despite recentadvancements in metagenomics, much of their biodiversity remains uncharacterized. Here wereport a data set of 27,346 marine virome contigs that includes 44 complete genomes. Theseoutnumber all currently known phage genomes in marine habitats and include members ofpreviously uncharacterized lineages. We designed a new method for host prediction based onco-occurrence associations that reveals these viruses infect dominant members of the marinemicrobiome such as Prochlorococcus and Pelagibacter. A negative association between hostabundance and the virus-to-host ratio supports the recently proposed Piggyback-the-Winnermodel of reduced phage lysis at higher host densities. An analysis of the abundance patternsof viruses throughout the oceans revealed how marine viral communities adapt to variousseasonal, temperature and photic regimes according to targeted hosts and the diversity ofauxiliary metabolic genes