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

Aureococcus anophagefferens represents one component of a model host-virus system (with the "giant virus" Kratosvirus quantuckense). Studies to define its ribocell (uninfected cells) and virocell (virus-infected cells) forms are needed, as both are abundant during algal blooms. A linkage between light-derived energy, virus particle production and virocell formation has been noted. We explored how the time of day (morning, afternoon, late day) of virus-host contact shaped virocell ontogeny. In parallel, we explored the need for light derived energy in this mixotrophic plankter by inhibiting photosystem II (PSII). Using flow cytometry and photochemical assessments, we examined the physiology of infected cells and controls, and estimated virus particle production by virocells. We observed distinct differences between ribocell and virocell response to treatments, including reductions in virus particle production during reduced light (i.e., duration) and PSII inhibition. Collectively this work demonstrates the importance of light in shaping the fate of infected cells and provides insight into the factors that constrain in situ blooms. Most significantly, we show that time of 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 future bloom modeling work.