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Abstract 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. 

Viruses of eukaryotic algae have become an important research focus due to their role(s) in nutrient cycling and top-down control of algal blooms. Omics-based studies have identified a boon of genomic and transcriptional potential among theNucleocytoviricota, a phylum of large dsDNA viruses which have been shown to infect algal and non-algal eukaryotes. However, little is still understood regarding the infection cycle of these viruses, particularly in how they take over a metabolically active host and convert it into a virocell state. Of particular interest are the roles light and the diel cycle in virocell development. Yet despite such a large proportion ofNucleocytoviricotainfecting phototrophs, little work has been done to tie infection dynamics to the presence, and absence, of light. Here, we examine the role of the diel cycle on the physiological and transcriptional state of the pelagophyteAureococcus anophagefferenswhile undergoing infection byKratosvirus quantuckensestrain AaV. Our observations demonstrate how infection by the virus interrupts the diel growth and division of this cell strain, and that infection further complicates the system by enhancing export of cell biomass. 

ABSTRACT Here, we report the draft genome ofAureococcus anophagefferensstrain CCMP1851, which is susceptible to the virusKratosvirus quantuckense. CCMP1851 complements an available genome for a virus-resistant strain (CCMP1850) isolated from the same bloom. Future studies can now use this genome to examine genetic hints of virus resistance and susceptibility. 

Abstract Cyanobacterial blooms dominated by Microcystis spp. pose significant ecological challenges, including the release of toxins and disruption of aquatic food webs. Although Microcystis can exist as free-living single cells or within dense mucilaginous colonies, the drivers and consequences of colony formation remain unclear. Here, we integrated metatranscriptomic datasets from two Microcystis bloom events in Lake Taihu, China, to analyze and to support findings on the functional differences between colonial and single-cell Microcystis. Our results confirmed colony expression profiles were disproportionately enriched in Microcystis transcripts compared to other prokaryotic taxa. This pattern exhibits Black Queen-like dynamics, where Microcystis assumes greater metabolic and defensive roles while associated bacteria reduce their transcriptional activity. Concomitantly, viral infection strategies diverged by Microcystis community morphology: colony-associated cells expressed lysogeny-associated genes, whereas single cells exhibited increased signatures of lytic infection. These data are consistent with the hypothesis that Microcystis colonies foster conditions favorable to lysogen formation—likely due to local high cell densities and the resulting advantage of superinfection immunity—whereas solitary cells experience stronger lytic pressure. On a broader scale, our findings refine the understanding of bloom dynamics by identifying how community morphological states coincide with distinct host–virus interactions. Cumulatively, this work underscores the importance of colony formation in shaping Microcystis ecology and highlights the need for further mechanistic studies to disentangle the complex interplay between phage infection modes, colony formation, and microbial community structure. 

ABSTRACT Here, we report on the raw and coassembled metatranscriptomes of 39 Lake Erie surface (1.0 m) water samples collected over a 2-day diel period encompassing episodic weather and bloom events. Preliminary taxonomic annotations and read mappings revealed thatMicrocystisspp. accounted for up to ~47% of the transcriptionally active community. 

Since the discovery of the first “giant virus,” particular attention has been paid toward isolating and culturing these large DNA viruses throughAcanthamoebaspp. bait systems. While this method has allowed for the discovery of plenty novel viruses in theNucleocytoviricota, 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-amoebalNucleocytoviricotashould be considered a focal point in viral ecology. In this review, we report onKratosvirus quantuckense(née Aureococcus anophagefferens Virus), an algae-infecting virus of theImitervirales. Current systems for study in theNucleocytoviricotadiffer 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 ofK. 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. 

Abstract The rediscovery of diatom blooms embedded within and beneath the Lake Erie ice cover (2007–2012) ignited interest in psychrophilic adaptations and winter limnology. Subsequent studies determined the vital role ice plays in winter diatom ecophysiology as diatoms partition to the underside of ice, thereby fixing their location within the photic zone. Yet, climate change has led to widespread ice decline across the Great Lakes, with Lake Erie presenting a nearly “ice-free” state in several recent winters. It has been hypothesized that the resultant turbid, isothermal water column induces light limitation amongst winter diatoms and thus serves as a competitive disadvantage. To investigate this hypothesis, we conducted a physiochemical and metatranscriptomic survey that spanned spatial, temporal, and climatic gradients of the winter Lake Erie water column (2019–2020). Our results suggest that ice-free conditions decreased planktonic diatom bloom magnitude and altered diatom community composition. Diatoms increased their expression of various photosynthetic genes and iron transporters, which suggests that the diatoms are attempting to increase their quantity of photosystems and light-harvesting components (a well-defined indicator of light limitation). We identified two gene families which serve to increase diatom fitness in the turbid ice-free water column: proton-pumping rhodopsins (a potential second means of light-driven energy acquisition) and fasciclins (a means to “raft” together to increase buoyancy and co-locate to the surface to optimize light acquisition). With large-scale climatic changes already underway, our observations provide insight into how diatoms respond to the dynamic ice conditions of today and shed light on how they will fare in a climatically altered tomorrow.