Viral diversity and dynamics in the open ocean

Abstract

In the open oceans that cover roughly 40% of our planet, viruses influence ecosystem dynamics, microbial diversity, and biogeochemical cycling. By infecting and killing cellular hosts, viruses transform organic matter from living cells into dissolved and particulate pools that fuel organic matter recycling and export. Despite their importance, viruses in the environment remain unexplored relative to other microbes, particularly in the under-sampled open oceans that might contain large reservoirs of novel viral diversity. For example, some fundamental questions remain open in this field: how many different viral populations coexist in the open ocean, what novel genes do they encode, and how do viral diversity and virus-host interactions vary from the surface to the deep ocean, or between free-living and particle-attached habitats? To address these questions, I explored the diversity and dynamics of viruses in the open ocean, from planktonic assemblages in the upper ocean to sinking particles in the deep sea. In this body of work, I used metagenomic approaches to study viruses sampled from Station ALOHA located in the North Pacific Subtropical Gyre. From roughly 7 TB of sequencing data, I recovered over 17,000 viral population genomes, at least 9,000 of which were novel with respect to what has been studied before. I explored how viral diversity, viral reproductive strategies, and virus-host interactions varied across vertical gradients along the open ocean water column to better understand viral effects on ecosystem dynamics and biogeochemical cycling. The culmination of these projects reveals the diversity and dynamics of viruses that represent some of the most abundant yet understudied life forms in the ocean.