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Abstract TheMicrocystismobilome is a well-known but understudied component of this bloom-forming cyanobacterium. Through genomic and transcriptomic comparisons, we found five families of transposases that altered the expression of genes in the well-studied toxigenic type-strain,Microcystis aeruginosaPCC 7086, and a non-toxigenic genetic mutant,Microcystis aeruginosaPCC 7806 ΔmcyB. Since its creation in 1997, the ΔmcyBstrain has been used in comparative physiology studies against the wildtype strain by research labs throughout the world. Some differences in gene expression between what were thought to be otherwise genetically identical strains have appeared due to insertion events in both intra- and intergenic regions. In our ΔmcyBisolate, a sulfate transporter gene cluster (sbp-cysTWA) showed differential expression from the wildtype, which may have been caused by the insertion of a miniature inverted repeat transposable element (MITE) in the sulfate-binding protein gene (sbp). Differences in growth in sulfate-limited media also were also observed between the two isolates. This paper highlights howMicrocystisstrains continue to “evolve” in lab conditions and illustrates the importance of insertion sequences / transposable elements in shaping genomic and physiological differences betweenMicrocystisstrains thought otherwise identical. This study forces the necessity of knowing the complete genetic background of isolates in comparative physiological experiments, to facilitate the correct conclusions (and caveats) from experiments. 

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 Here we report the complete, closed genome of the non-toxicMicrocystis aeruginosaPCC7806 ΔmcyBmutant strain. This genome is 5,103,923 bp long, with a GC content of 42.07%. Compared to the published wild-type genome (Microcystis aeruginosaPCC7806SL), there is evidence of accumulated mutations beyond the inserted chloramphenicol resistance marker. 

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. Here, we report the genomic sequence of Aureococcus anophagefferens virus, assembled into one circular contig from both Nanopore and Illumina reads. The genome is 381,717 bp long with a GC content of 29.1%, which includes an additional 5-kb region between the previously predicted polar ends of the reference genome. 

ABSTRACT Here, we report the assembled and annotated genome of the freshwater diatom Fragilaria crotonensis SAG 28.96. The 61.85-Mb nuclear genome was assembled into 879 contigs, has a GC content of 47.40%, contains 26,015 predicted genes, and shows completeness of 81%. 

Harmful algal blooms (HABs) caused by the toxin-producing cyanobacteria Microcystis spp., can increase water column pH. While the effect(s) of these basified conditions on the bloom formers are a high research priority, how these pH shifts affect other biota remains understudied. Recently, it was shown these high pH levels decrease growth and Si deposition rates in the freshwater diatom Fragilaria crotonensis and natural Lake Erie (Canada-US) diatom populations. However, the physiological mechanisms and transcriptional responses of diatoms associated with these observations remain to be documented. Here, we examined F. crotonensis with a set of morphological, physiological, and transcriptomic tools to identify cellular responses to high pH. We suggest 2 potential mechanisms that may contribute to morphological and physiological pH effects observed in F. crotonensis . Moreover, we identified a significant upregulation of mobile genetic elements in the F. crotonensis genome which appear to be an extreme transcriptional response to this abiotic stress to enhance cellular evolution rates–a process we have termed “ genomic roulette. ” We discuss the ecological and biogeochemical effects high pH conditions impose on fresh waters and suggest a means by which freshwater diatoms such as F. crotonensis may evade high pH stress to survive in a “basified” future.