Virus Infections of Eukaryotic Marine Microbes

Marine viruses serve as engineers of microbial genetic diversity, agents of mortality and drivers of global biogeochemical cycles. At any one point in time up to half of marine microbes are virus- infected. However, our understanding of how viruses interact with their eukaryotic microbial hosts is primarily limited to acute infections that ultimately result in cell death. Similarly, estimates of the global impact of viruses on elemental cycling are based solely on cell lysis events despite evidence that viruses manipulate and alter host metabolism. The research presented herein explores the potential for non-fatal (persistent) virus infections in marine protists, variables that may influence infection dynamics and the impact of acute virus infections on cellular biochemical composition. A dual screening approach using analytical flow cytometry and analysis of publicly available transcriptome sequence data was used to detect novel persistent viruses in eukaryotic marine microbe monocultures. Putative viruses were detected in half of phytoplankton strains examined via analytical flow cytometry and electron microscopy. Sequence-based inquiries revealed that approximately one third of cultures contained viral sequences. Further exploration of transcriptome data from the coccolithophore Pleurochrysis carterae and the dinoflagellate Scrippsiella trochoidea revealed numerous sequences with high similarity to algal viruses and suggested the potential for dynamic molecular-scale interactions between persistent viruses and marine eukaryotic phytoplankton. To evaluate the impact of virus infection upon phytoplankton cellular biochemical composition, a range of particulate and dissolved chemical compounds were measured over high temporal resolution during early infection stages in the Emiliania huxleyi-virus model system (CCMP 374-EhV-86). Acute virus infection led to rapid and significant changes in host cell biochemistry including decreased photosynthetic capacity, release of cellular dimethylsulfonioproprionate (DMSP) and subsequent increases in dissolved dimethyl sulfide (DMS). Biochemical modifications of host cells early in infection cycles may influence the transfer of carbon among trophic levels and affect the global flux of elements such as sulfur, carbon and oxygen. Taken together, these data demonstrate that the influence of marine viruses extends beyond effects associated with microbial cell death