Biogeochemical consequences of diatom-virus interactions in the California Current Ecosystem

Diatoms are one of the most widely distributed and ecologically successful groups of organisms in the modern ocean and are responsible for up to 40% of the global marine primary productivity. Given their obligate silicon (Si) requirement for cell wall formation, diatoms effectively couple the Si and carbon (C) cycles, converting dissolved Si into biogenic silica that ballasts substantial vertical flux of C out of the euphotic zone into the mesopelagic and deep ocean. Viruses are key players in ocean biogeochemical cycles, yet little is known about how viruses specifically impact diatom populations. Our findings demonstrate that Si limitation facilitates virus infection and mortality in diatoms in the highly productive coastal waters of the California Current Ecosystem. We diagnosed early, active and lytic stages of viral infection across a gradient of Si stress, using metatranscriptomic analyses of cell-associated diatom viruses and targeted, quantitative PCR of free, extracellular viruses alongside a suite of biogeochemical diagnostics. In Si-limited cultures of the centric, bloom-forming diatom, Chaetoceros tenuissimus, viral-induced mortality was accelerated relative to Si-replete cultures, with unimpaired viral production. Together, these findings contextualize diatom-infecting viruses within the ecophysiological framework of silicon availability and diatom-mediated biogeochemical cycling.