Laboratory Culture-Based Characterization of the Resting Stage Cells of the Brown-Tide-Causing Pelagophyte, Aureococcus anophagefferens

Let's talk about sex: Why reproductive systems matter for understanding algae

Sex is a crucial process that has molecular, genetic, cellular, organismal, and population-level consequences for eukaryotic evolution. Eukaryotic life cycles are composed of alternating haploid and diploid phases but are constrained by the need to accommodate the phenotypes of these different phases. Critical gaps in our understanding of evolutionary drivers of the diversity in algae life cycles include how selection acts to stabilize and change features of the life cycle. Moreover, most eukaryotes are partially clonal, engaging in both sexual and asexual reproduction. Yet, our understanding of the variation in their reproductive systems is largely based on sexual reproduction in animals or angiosperms. The relative balance of sexual versus asexual reproduction not only controls but also is in turn controlled by standing genetic variability, thereby shaping evolutionary trajectories. Thus, we must quantitatively assess the consequences of the variation in life cycles on reproductive systems. Algae are a polyphyletic group spread across many of the major eukaryotic lineages, providing powerful models by which to resolve this knowledge gap. There is, however, an alarming lack of data about the population genetics of most algae and, therefore, the relative frequency of sexual versus asexual processes. For many algae, the occurrence of sexual reproduction is unknown, observations have been lost in overlooked papers, or data on population genetics do not yet exist. This greatly restricts our ability to forecast the consequences of climate change on algal populations inhabiting terrestrial, aquatic, and marine ecosystems. This perspective summarizes our extant knowledge and provides some future directions to pursue broadly across micro- and macroalgal species.

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.

Harmful algal blooms in China: History, recent expansion, current status, and future prospects

The impacts of harmful algal blooms (HABs) on economies, public health, ecosystems, and aquaculture across the globe have all increased in recent decades, and this has been acutely the case in China. Here, we review the history of HABs and HABs research in China, as well as recent trends in HABs and future prospects of HAB science in China. The most updated analyses demonstrated that the number of HAB events, the number of HAB species, the aerial coverage of HABs, and the impacts of HABs in Chinese waters during the 21st century were all higher than that during the last two decades of the 20th century. The increase in the number of HABs in China has been significantly correlated with the increased discharge of ammonium and total phosphorus into coastal waters (p < 0.01 for both). Notable newly recognized events this century have included chronic HABs caused by Prorocentrum donghaiense and Karenia mikimotoi, a paralytic shellfish poisoning event caused by Gymnodinium catenatum that sickened 80 people, brown tides caused by Aureococcus anophagefferens, green tides caused by Ulva prolifera, golden tides caused by Sargassum horneri, and the disruption of a nuclear power plant caused by a bloom of Phaeocystis globosa. A series of key discoveries regarding HABs has been made this century including documentation of nearly all known HAB toxins in Chinese waters, discovery of novel cyst-formation and/or life stages of multiple HABs-causing species, identification of the chemical and physical oceanographic drivers of multiple HABs including those formed by P. donghaiense, K. mikimotoi, and U. prolifera, and the successful mitigation of HABs via the use of modified clay approaches. Future research prospects highlighted include the use of macroalgae as a means to prevent, mitigate, and control (PCM) HABs and the process by which multi-disciplinary studies involving molecular approaches (omics), remote in situ detection, artificial intelligence, and mega-data analyses might be used to develop refined and realistic HAB forecasting platforms. Collectively, this review demonstrates the significant evolution of HAB science since the 20th century in China and demonstrates that while HABs in China are complex and widespread, recent and on-going discoveries make the development of detailed understanding and effective measures to mitigate the negative effects of HABs a hopeful outcome in the coming years.

Aureococcus anophagefferens (Pelagophyceae) genomes improve evaluation of nutrient acquisition strategies involved in brown tide dynamics

The pelagophyte Aureococcus anophagefferens causes harmful brown tide blooms in marine embayments on three continents. Aureococcus anophagefferens was the first harmful algal bloom species to have its genome sequenced, an advance that evidenced genes important for adaptation to environmental conditions that prevail during brown tides. To expand the genomic tools available for this species, genomes for four strains were assembled, including three newly sequenced strains and one assembled from publicly available data. These genomes ranged from 57.11 to 73.62 Mb, encoding 13,191-17,404 potential proteins. All strains shared ~90% of their encoded proteins as determined by homology searches and shared most functional orthologs as determined by KEGG, although each strain also possessed coding sequences with unique functions. Like the original reference genome, the genomes assembled in this study possessed genes hypothesized to be important in bloom proliferation, including genes involved in organic compound metabolism and growth at low light. Cross-strain informatics and culture experiments suggest that the utilization of purines is a potentially important source of organic nitrogen for brown tides. Analyses of metatranscriptomes from a brown tide event demonstrated that use of a single genome yielded a lower read mapping percentage (~30% of library reads) as compared to a database generated from all available genomes (~43%), suggesting novel information about bloom ecology can be gained from expanding genomic space. This work demonstrates the continued need to sequence ecologically relevant algae to understand the genomic potential and their ecology in the environment.

Taxonomy and Ecology of Marine Algae

The term “algae” refers to a large diversity of unrelated phylogenetic entities, ranging from picoplanktonic cells to macroalgal kelps [...]

Exploration of resting cysts (stages) and their relevance for possibly HABs-causing species in China

The studies on the species diversity, distribution, environmental implications, and molecular basis of resting cysts (stages) of dinoflagellates and a few species of other groups conducted in China during the last three decades are reviewed. The major achievements are summarized as the following five aspects: 1) The continual efforts in detecting the species diversity of resting cysts (spores) in dinoflagellates and other classes using either morphological or molecular approaches, or both, in the four seas of China, which led to identifications of 106 species of dinoflagellate resting cysts and 4 species of resting stages from other groups of microalgae, with a total of 64 species of dinoflagellate cysts and the resting stage of the brown tide-causing Aureococcus anophagefferens being unequivocally identified via molecular approaches from the sediments of Chinese coastal waters; 2) The well-known toxic and HABs-causing dinoflagellates Karenia mikimotoi, Karlodinium veneficum, Akashiwo sanguinea and the pelagophyte A. anophagefferens were proven to be resting cyst (stage) producers via laboratory studies on their life cycles and field detections of resting cysts (resting stage cells). And, via germination experiment and subsequent characterization of vegetative cells, numerous dinoflagellate species that had never been described or found to form cysts were discovered and characterized; 3) The distributions of the resting cysts of Alexandrium catenella, A. pacificum, Gymnodinium catenatum, K. mikimotoi, K. veneficum and Azadinium poporum and the resting stage cells of A. anophagefferens were morphologically and molecularly mapped in all four seas of China, with A. anophagefferens proven to have been present in the Bohai Sea for at least 1,500 years; 4) Obtaining important insights into the 'indicator' values of the dinoflagellate cyst assemblages in sediment cores for tracking eutrophication, environmental pollution and other anthropological influences in coastal waters; 5) Studies on the cyst-pertinent processes and genetic basis (transcriptomics together with physiological and chemical measurements) of resting cyst dormancy not only revealed the regulating patterns of some environmental factors in cyst formation and germination, but also identified many characteristically active or inactive metabolic pathways, differentially expressed genes, and the possibly vital regulating function of the phytohormone abscisic acid and a group of molecular chaperones in resting cysts. We also identified seven issues and three themes that should be addressed and explored by Chinese scientists working in the area in the future.