Viral infection dynamics in marine diatoms across environmental and ecophysiological gradients

Diatoms are a diverse and widespread group of aquatic, photosynthetic, eukaryotic microorganisms. Key players in the global carbon cycle, diatoms contribute ~20% of the primary production on the planet and facilitate substantial export of particulate organic carbon out of the surface into the deep ocean. While viruses are considered catalysts of ecological, evolutionary, and biogeochemical process in the ocean, very little is known about the specific viruses that infect diatoms. Using both lab and field-based approaches, and a combination of molecular, physiological, and geochemical techniques, we are exploring the ecophysiological frameworks that shape diatom host-virus interactions. In the northeast Pacific Ocean, we found that silicon limitation facilitated virus infection and mortality in diatoms while the onset of iron limitation, in sharp contrast, substantially reduced viral replication. Cell-associated diatom viruses were also notably low in abundance and diversity in a chronically Fe-limited region of the subarctic northeast Pacific. These relationships were also observed in laboratory experiments with the model, bloom-forming, centric diatom, Chaetoceros tenuissimus, and together, contextualize diatom viruses within the ecophysiological framework of nutrient availability. These findings highlight the dynamic role that nutrient-driven host–virus interactions play in determining diatom fate in the ocean.