Time of day of infection shapes development of a eukaryotic algal-Nucleocytoviricota virocell.

Aureococcus anophagefferens forms a model host-virus system with the "giant virus" Kratosvirus quantuckense. Studies to define its ribocell (uninfected) and virocell (virus-infected) forms are needed as these states co-occur during algal blooms. Previously, a link between light-derived energy, virus particle production, and virocell formation was noted. We explored how the time of day (morning, midday, or late day) of virus-host contact shaped virocell ontogeny. In parallel, we explored the dependence on light-derived energy in this mixotrophic plankter by inhibiting photosystem II, testing the role of heterotrophic energy in infection dynamics. Using flow cytometry and photochemical assessments, we examined the physiology of infected cells and controls, and estimated virus particle production. We observed differences between ribocell and virocell response to treatments, including reductions in virus particle production during reduced light duration) and PSII inhibition (i.e. "forced heterotrophy"). This work demonstrates the importance of light in shaping the fate of infected cells and provides insight into factors that constrain in situ blooms. Most significantly, we show that time of the solar day when a virus and host come into contact influences viral particle production, and therefore bloom dynamics; a factor that needs to be considered in bloom modeling work.

Kratosvirus quantuckense: the history and novelty of an algal bloom disrupting virus and a model for giant virus research.

Since the discovery of the first "giant virus," particular attention has been paid toward isolating and culturing these large DNA viruses through Acanthamoeba spp. bait systems. While this method has allowed for the discovery of plenty novel viruses in the Nucleocytoviricota, environmental -omics-based analyses have shown that there is a wealth of diversity among this phylum, particularly in marine datasets. The prevalence of these viruses in metatranscriptomes points toward their ecological importance in nutrient turnover in our oceans and as such, in depth study into non-amoebal Nucleocytoviricota should be considered a focal point in viral ecology. In this review, we report on Kratosvirus quantuckense (née Aureococcus anophagefferens Virus), an algae-infecting virus of the Imitervirales. Current systems for study in the Nucleocytoviricota differ significantly from this virus and its relatives, and a litany of trade-offs within physiology, coding potential, and ecology compared to these other viruses reveal the importance of K. quantuckense. Herein, we review the research that has been performed on this virus as well as its potential as a model system for algal-virus interactions.