Environmental Factors Modulate Saxitoxins (STXs) Production in Toxic Dinoflagellate Alexandrium: An Updated Review of STXs and Synthesis Gene Aspects.

The marine dinoflagellate Alexandrium is known to form harmful algal blooms (HABs) and produces saxitoxin (STX) and its derivatives (STXs) that cause paralytic shellfish poisoning (PSP) in humans. Cell growth and cellular metabolism are affected by environmental conditions, including nutrients, temperature, light, and the salinity of aquatic systems. Abiotic factors not only engage in photosynthesis, but also modulate the production of toxic secondary metabolites, such as STXs, in dinoflagellates. STXs production is influenced by a variety of abiotic factors; however, the relationship between the regulation of these abiotic variables and STXs accumulation seems not to be consistent, and sometimes it is controversial. Few studies have suggested that abiotic factors may influence toxicity and STXs-biosynthesis gene (sxt) regulation in toxic Alexandrium, particularly in A. catenella, A. minutum, and A. pacificum. Hence, in this review, we focused on STXs production in toxic Alexandrium with respect to the major abiotic factors, such as temperature, salinity, nutrients, and light intensity. This review informs future research on more sxt genes involved in STXs production in relation to the abiotic factors in toxic dinoflagellates.

Development of saxitoxin biosynthesis gene sxtB-targeted qPCR assay for the quantification of toxic dinoflagellates Alexandrium catenella (group I) and A. pacificum (group IV) occurring in the Korean coast.

Toxic dinoflagellate Alexandrium can produce saxitoxins (STXs) and cause paralytic shellfish poisoning (PSP), and thus they are monitored for environmental safety management. Microscopic discrimination of dinoflagellates is difficult to distinguish between toxic and non-toxic species due to their similar morphology. Meanwhile, an alternative quantitative PCR (qPCR) assay is sensitive, rapid, and cost-effective for harmful species monitoring. Herein, we developed a novel qPCR assay to detect the STXs biosynthesis gene sxtB of Alexandrium catenella and A. pacificum, the leading cause of PSP outbreaks in Asian coasts and worldwide. The newly designed sxtB TaqMan probes target the species without any positive signal in other relative dinoflagellates. Deming regression analysis revealed that the sxtB copy number of A. catenella and A. pacificum was 3.6 and 4.1 copies per cell, respectively. During the blooming periods (April 13th-14th, 2020), only A. catenella cells were detected through the qPCR assay, ranging from 5.0 × 10 to 2.5 × 104 eq cells L-1. In addition, sxtB qPCR quantified more accurately compared to large subunit (LSU) rRNA targeting qPCR assay that overestimate cell density. Besides, the sensitivity of sxtB was higher compared to the microscope when the species were rarely present (5.0 × 102 cells L-1). These suggest that the sxtB qPCR assay can be applied to toxic Alexandrium monitoring in the Korean coast, even in the early stage of bloomings.

Polyphyletic origin of saxitoxin biosynthesis genes in the marine dinoflagellate Alexandrium revealed by comparative transcriptomics.

The marine dinoflagellate Alexandrium is known to form harmful algal blooms, and at least 14 species within the genus can produce saxitoxins (STXs). STX biosynthesis genes (sxt) are individually revealed in toxic dinoflagellates; however, the evolutionary history remains controversial. Herein, we determined the transcriptome sequences of toxic Alexandrium (A. catenella and A. pacificum) and non-toxic Alexandrium (A. fraterculus and A. fragae) and characterized their sxt by focusing on evolutionary events and STX production. Comparative transcriptome analysis revealed higher homology of the sxt in toxic Alexandrium than in non-toxic species. Notably, non-toxic Alexandrium spp. were found to have lost two sxt core genes, namely sxtA4 and sxtG. Expression levels of 28 transcripts related to eight sxt core genes showed that sxtA, sxtG, and sxtI were relatively high (>1.5) in the toxic group compared to the non-toxic group. In contrast, the non-toxic group showed high expression levels in sxtU (1.9) and sxtD (1.7). Phylogenetic tree comparisons revealed distinct evolutionary patterns between 28S rDNA and sxtA, sxtB, sxtI, sxtD, and sxtU. However, similar topology was observed between 28S rDNA, sxtS, and sxtH/T. In the sxtB and sxtI phylogeny trees, toxic Alexandrium and cyanobacteria were clustered together, separating from non-toxic species. These suggest that Alexandrium may acquire sxt genes independently via horizontal gene transfer from toxic cyanobacteria and other multiple sources, demonstrating monocistronic transcripts of sxt in dinoflagellates.

Nuclear genome of dinoflagellates: Size variation and insights into evolutionary mechanisms.

Recent progress in high-throughput sequencing technologies has dramatically increased availability of genome data for prokaryotes and eukaryotes. Dinoflagellates have distinct chromosomes and a huge genome size, which make their genomic analysis complicated. Here, we reviewed the nuclear genomes of core dinoflagellates, focusing on the genome and cell size. Till now, the genome sizes of several dinoflagellates (more than 25) have been measured by certain methods (e.g., flow cytometry), showing a range of 3-250 pg of genomic DNA per cell. In contrast to their relatively small cell size, their genomes are huge (about 1-80 times the human haploid genome). In the present study, we collected the genome and cell size data of dinoflagellates and compared their relationships. We found that dinoflagellate genome size exhibits a positive correlation with cell size. On the other hand, we recognized that the genome size is not correlated with phylogenetic relatedness. These may be caused by genome duplication, increased gene copy number, repetitive non-coding DNA, transposon expansion, horizontal gene transfer, organelle-to-nucleus gene transfer, and/or mRNA reintegration into the genome. Ultimate verification of these factors as potential causative mechanisms would require sequencing of more dinoflagellate genomes in the future.

Two novel glutathione S-transferase (GST) genes in the toxic marine dinoflagellate Alexandrium pacificum and their transcriptional responses to environmental contaminants.

The present study identified two novel glutathione S-transferase (GST) genes from the toxic dinoflagellate Alexandrium pacificum and examined their molecular characteristics and transcriptional responses to algicides and environmental contaminants. Bioinformatic analysis revealed that both ApGSTs are cytosolic, belonging to the chi-like class (ApGST1) and an undefined class (ApGST2). The overall expression of ApGSTs showed similar patterns depending on the exposed contaminants, while they were differently regulated by polychlorinated biphenyl (PCB). Copper treatments (CuCl2 and CuSO4) did not significantly induce the expression of ApGSTs. The highest up-regulations of ApGST1 and ApGST2 were under 6-h treatments of 0.10 and 0.50 mg L-1 NaOCl. Interestingly, only ApGST1 increased significantly after 0.10, 0.50, and 1.00 mg L-1 of PCB exposure (6 h). Intracellular reactive oxygen species (ROS) increased considerably under NaOCl; however, it was not significantly higher in the PCB-treated cells. GST activity was increased by NaOCl and PCB treatments, but only PCB caused apoptosis. These results suggest that GSTs are involved in the first line of phase II detoxification, protecting dinoflagellate cells against oxidative damage.

Effects of nitrate on the saxitoxins biosynthesis revealed by sxt genes in the toxic dinoflagellate Alexandrium pacificum (group IV).

The dinoflagellate Alexandrium pacificum (group IV) is of particular interest because of its involvement in harmful algal blooms and production of saxitoxin (STX), which causes paralytic shellfish poisoning. The toxicity from STX and its analogues (STXs) is suspected to be affected by nitrogen (N) availability. However, the toxicity-associated behavior and STX-biosynthesis gene responses of the toxic A. pacificum under N fluctuations have not been sufficiently investigated. In the present study, we identified the sxtI gene involved in sxt biosynthesis pathway and evaluated the effects of nitrate (NO3-) on STXs production and the expression of four sxt core genes (sxtA4, sxtG, sxtB, and sxtI). Quantification of total STXs levels in the cultures under different NO3- regimes showed that NO3- concentration influenced STXs production. In addition, the proportion and concentration of STXs varied depending on the NO3- concentration. Core sxt transcript abundance was also influenced by available NO3- in a time-dependent manner. Expressional levels and patterns of sxtI were correlated with those of sxtA and sxtB. The relationship between the toxins and sxt responses in A. pacificum under various NO3- regimes suggests the direct involvement of N in the STXs biosynthesis pathway. Understanding this link would provide a tool to understand the toxin dynamics of dinoflagellates following N shifts in marine environments.

Immunomodulatory, Antioxidant, Anticancer, and Pharmacokinetic Activity of Ulvan, a Seaweed-Derived Sulfated Polysaccharide: An Updated Comprehensive Review.

Cancer is one of the most worldwide spread diseases and causes maximum death. Treatment of cancer depends on the host immune system and the type of drugs. The inefficiency of conventional cancer treatments as a result of drug resistance, nontargeted delivery, and chemotherapy-related negative side effects has caused bioactive phytochemicals to come into focus. As a result, recent years have seen an increase in research into screening and identifying natural compounds with anticancer properties. Recent studies on the isolation and use of polysaccharides derived from various marine algal species have revealed a variety of biological activities, including antioxidant and anticancer properties. Ulvan is a polysaccharide derived from various green seaweeds of the Ulva species in the family Ulvaceae. It has been demonstrated to have potent anticancer and anti-inflammatory properties through the modulation of antioxidants. It is vital to understand the mechanisms underlying the biotherapeutic activities of Ulvan in cancer and its role in immunomodulation. In this context, we reviewed the anticancer effects of ulvan based on its apoptotic effects and immunomodulatory activity. Additionally, we also focused on its pharmacokinetic studies in this review. Ulvan is the most conceivable candidate for use as a cancer therapeutic agent and could be used to boost immunity. Moreover, it may be established as an anticancer drug once its mechanisms of action are understood. Due to its high food and nutritive values, it can be used as a possible dietary supplement for cancer patients in the near future. This review may provide fresh perspectives on the potential novel role of ulvan, reveal a brand-new cancer-prevention strategy, and improve human health.

Ship Hull-Fouling Diatoms on Korean Research Vessels Revealed by Morphological and Molecular Methods, and Their Environmental Implications.

Ship biofouling is one of the main vectors for the introduction and global spread of non-indigenous organisms. Diatoms were the early colonizers of ship hulls; however, their community composition on ships is poorly understood. Herein, we investigated the diatom community on the hull samples collected from two Korean research vessels Isabu (IRV) and Onnuri (ORV) on September 2 and November 10, 2021, respectively. IRV showed low cell density (345 cells/cm2) compared to ORV (778 cells/cm2). We morphologically identified more than 15 species of diatoms from the two research vessels (RVs). The microalgae in both RVs were identified as Amphora, Cymbella, Caloneis, Halamphora, Navicula, Nitzschia, and Plagiogramma. Of them, the genus Halamphora was found to be predominant. However, both RVs had a varied dominant species with a significant difference in body size; Halamphora oceanica dominated at IRV, and Halamphora sp. at ORV, respectively. Molecular cloning showed similar results to morphological analysis, in which Halamphora species dominated in both RVs. The hull-attached species were distinct from species found in the water column. These results revealed diatoms communities that are associated with ship hull-fouling at an early stage of biofilm formation. Moreover, ships arriving from different regions could show some variation in species composition on their hull surfaces, with the potential for non-indigenous species introduction.

Antioxidant and chemotherapeutic efficacies of seaweed-derived phlorotannins in cancer treatment: A review regarding novel anticancer drugs.

The ineffectiveness of traditional cancer therapies due to drug resistance, nontargeted delivery, and chemotherapy-associated adverse side effects has shifted attention to bioactive phytochemicals. Consequently, research efforts toward screening and identification of natural compounds with anticancer properties have increased in recent years. Marine seaweed-derived bioactive compounds, such as polyphenolic compounds, have exhibited anticancer properties. Phlorotannins (PTs), a major group of seaweed-derived polyphenolic compounds, have emerged as powerful chemopreventive and chemoprotective compounds, regulating apoptotic cell death pathways both in vitro and in vivo. In this context, this review focuses on the anticancer activity of polyphenols isolated from brown algae, with a special reference to PTs. Furthermore, we highlight the antioxidant effects of PTs and discuss how they can impact cell survival and tumor development and progression. Moreover, we discussed the potential therapeutic application of PTs as anticancer agents, having molecular mechanisms involving oxidative stress reduction. We have also discussed patents or patent applications that apply PTs as major components of antioxidant and antitumor products. With this review, researcher may gain new insights into the potential novel role of PTs, as well as uncover a novel cancer-prevention mechanism and improve human health.

Biological activity of algal derived carrageenan: A comprehensive review in light of human health and disease.

Carrageenans are a family of natural linear sulfated polysaccharides derived from red seaweeds and used as a common food additive. Carrageenan's properties, impact on health, and aesthetic benefits have all been studied for a long time; however, the mechanisms are still unclear. In pharmaceutical aspects, carrageenan displayed potential antioxidant and immunomodulatory properties in both in vivo and in vitro action. It also contributes to potential disease-preventive activities through dynamic modulation of important intracellular signaling pathways, regulation of ROS buildup, and preservation of major cell survival and death processes which leads to potential drug development. Furthermore, the chemical synthesis of the current bioactive medicine with confirmational rearrangement may increase availability and bioactivity needs diligent examination. In this review, we give an up-to-date overview of recent research on Carrageenan with reference to health and therapeutic advantages. In addition, we have focused on structural conformation and its primary strategic deployment in disease prevention, as well as the mechanistic investigation of how it functions to combat various disease-preventive employed for future therapeutic interventions. This review may get new insights into the possible novel role of carrageenan and open up a novel disease-preventive mechanism and enhance human health.

Saxitoxins-producing potential of the marine dinoflagellate Alexandrium affine and its environmental implications revealed by toxins and transcriptome profiling.

The marine dinoflagellate Alexandrium occurs widely in coastal waters, and some of them can produce saxitoxins (STXs) that cause paralytic shellfish poisoning (PSP). Alexandrium affine is a harmful algal bloom (HAB)-forming species off the coast of Asia; however, its ability to produce STXs has been controversial. In the present study, we detected STXs in A. affine Alex02 isolated from the southern coast of Korea. The total STXs equivalent (STXs eq) and profiles of Alex02 varied depending on the tested environmental conditions, including the temperature and nitrate concentrations. STXs toxicity levels of A. affine Alex02 (<0.8 STXs eq fmol cell-1) were significantly lower than those of toxic A. catenella Alex03 and A. pacificum Alex05. On a genetic basis, we identified all the STX biosynthesis sxt genes, except sxtX in A. affine, via large-scale transcriptome analysis. Interestingly, the two proteins, sxtA4 and sxtG, were similar in sequence and domain structure to those of other toxic dinoflagellates and cyanobacteria; however, their transcript levels were extremely low. Our results suggest that A. affine has the potential to produce STXs, while its toxicity is much lower or negligible, which is unlikely to cause PSP incidents in marine environments.

Two novel superoxide dismutase genes (CuZnSOD and MnSOD) in the toxic marine dinoflagellate Alexandrium pacificum and their differential responses to metal stressors.

Superoxide dismutase (SOD) is an important antioxidant enzyme that is involved in the first line of defense against reactive oxygen species (ROS) within cells. Herein, we determined two novel CuZnSOD and MnSOD genes from the toxic marine dinoflagellate Alexandrium pacificum (designated as ApCuZnSOD and ApMnSOD) and characterized their structural features and phylogenetic affiliations. In addition, we examined the relative gene expression and ROS levels following exposure to heavy metals. ApCuZnSOD encoded 358 amino acids (aa) with two CuZnSOD-conserved domains. ApMnSOD encoded 203 aa that contained a mitochondrial-targeting signal and a MnSOD signature motif but missed an N-terminal domain. Phylogenetic trees showed that ApCuZnSOD clustered with other dinoflagellates, whereas ApMnSOD formed a clade with green algae and plants. Based on the 72-h median effective concentration (EC50), A. pacificum showed toxic responses in the order of Cu, Ni, Cr, Zn, Cd, and Pb. SOD expression levels dramatically increased after 6 h of Pb (≥6.5 times) and 48 h of Cu treatment (≥3.9 times). These results are consistent with the significant increase in ROS production in the A. pacificum exposed to Pb and Cu. These suggest that the two ApSODs are involved in the antioxidant defense system but respond differentially to individual metals.

Immunomodulatory and anti-inflammatory and anticancer activities of porphyran, a sulfated galactan.

Seaweeds are high in bioactive chemicals frequently used to treat human illnesses. Porphyran is a polysaccharide found in the red seaweeds of the genus Porphyra. Porphyran has been discovered to have immunomodulatory, anti-inflammatory activity, and anti-cancer effects via boosting immunity and targeting important apoptotic molecules, making them potential chemotherapeutic or chemopreventive drugs. Polysaccharide-mediated dynamic control of apoptosis and autophagy in cancer has been a viable treatment with low cytotoxicity with high efficacy. Thus, comprehending the influence of porphyran on human health and their molecular mechanisms would open up a new paradigm in cancer therapies. Also, the importance of apoptotic/autophagy modulating porphyran in cancer therapy has been highlighted as the future direction of improved nano-formulation for improved clinical efficacy. This review focuses on the current research into porphyran's anti-cancer efficacy and putative mechanisms of action through apoptosis and autophagy in various cancers, as well as its potential chemotherapeutic treatment in near future.

The complete mitochondrial genome of the mauve stinger jellyfish Pelagia noctiluca Forskål, 1775 (Cnidaria, Scyphozoa, Semaeostomeae) with phylogenetic analysis.

This study determined the complete mitochondrial genome of the jellyfish Pelagia noctiluca (Scyphozoa, Semaeostomeae) for the first time. The genome was a linear molecule of 16,390 bp in length and 59.3% AT. It comprised of 13 typical protein-coding genes (cox1-3, nd1-6, nd4L, atp6, atp8, and cytB), two ribosomal RNAs (16S and 12S rRNA), and two tRNAs (trnM and trnW). In addition, we detected two additional open reading frames (polB and ORF314) at one end of the genome. The gene-coding structures were identical to those of other scyphozoans. Based on a molecular phylogeny constructed using 13 protein-coding genes, P. noctiluca has the closest genetic relationship with the genus Chrysaora (Semaeostomeae).

Population Genetic Structures and Demographic Expansion of the Exotic Jellyfish Carybdea brevipedalia in Korean Coasts Inferred from Mitochondrial COI Analysis.

Carybdea brevipedalia Kishinouye, 1891 is a poisonous jellyfish that usually occurs only in Japanese coastal regions. However, it was recently found on the Korean coast, thus expanding its known geographical range. In this study, we analyzed the population genetics and demographic histories of 113 C. brevipedalia specimens from the southern and eastern coastal regions of Korea by sequencing mitochondrial DNA cytochrome c oxidase subunit I (COI). We identified 42 C. brevipedalia COI haplotypes with high genetic diversity and a significant genetic structure. Populations were highly differentiated based on geographic location and distinctly divided into A and B clades. The results of Mantel tests indicated that geographic distance influenced the genetic distance between the two clades. Moreover, demographic analyses (neutrality tests) and the star-like profile of the Templeton, Crandall, and Sing (TCS) haplotype network indicated that C. brevipedalia had recently expanded into the southern and eastern coastal regions of Korea. These findings suggest that C. brevipedalia populations along the Korean coast have significant genetic differentiation that could be influenced by geographic isolation and subsequent adaptation to regional ecological conditions.

Microalgal Phycoremediation: A Glimpse into a Sustainable Environment.

Microalgae are continually exposed to heavy metals and metalloids (HMMs), which stifles their development and reproduction due to the resulting physiological and metabolic abnormalities, leading to lower crop productivity. They must thus change their way of adapting to survive in such a hostile environment without sacrificing their healthy growth, development, reproductive capacity, or survival. The mode of adaptation involves a complex relationship of signalling cascades that govern gene expression at the transcriptional and post-transcriptional levels, which consequently produces altered but adapted biochemical and physiochemical parameters. Algae have been reported to have altered their physicochemical and molecular perspectives as a result of exposure to a variety of HMMs. Hence, in this review, we focused on how microalgae alter their physicochemical and molecular characteristics as a tolerance mechanism in response to HMM-induced stress. Furthermore, physiological and biotechnological methods can be used to enhance extracellular absorption and clean up. The introduction of foreign DNA into microalgae cells and the genetic alteration of genes can boost the bio-accumulation and remediation capabilities of microalgae. In this regard, microalgae represent an excellent model organism and could be used for HMM removal in the near future.

Algal Phlorotannins as Novel Antibacterial Agents with Reference to the Antioxidant Modulation: Current Advances and Future Directions.

The increasing drug resistance of infectious microorganisms is considered a primary concern of global health care. The screening and identification of natural compounds with antibacterial properties have gained immense popularity in recent times. It has previously been shown that several bioactive compounds derived from marine algae exhibit antibacterial activity. Similarly, polyphenolic compounds are generally known to possess promising antibacterial capacity, among other capacities. Phlorotannins (PTs), an important group of algae-derived polyphenolic compounds, have been considered potent antibacterial agents both as single drug entities and in combination with commercially available antibacterial drugs. In this context, this article reviews the antibacterial properties of polyphenols in brown algae, with particular reference to PTs. Cell death through various molecular modes of action and the specific inhibition of biofilm formation by PTs were the key discussion of this review. The synergy between drugs was also discussed in light of the potential use of PTs as adjuvants in the pharmacological antibacterial treatment.

A state-of-the-art review on fucoidan as an antiviral agent to combat viral infections.

As a significant public health hazard with several drug side effects during medical treatment, searching for novel therapeutic natural medicines is promising. Sulfated polysaccharides from algae, such as fucoidan, have been discovered to have a variety of medical applications, including antibacterial and immunomodulatory properties. The review emphasized on the utilization of fucoidan as an antiviral agent against viral infections by inhibiting their attachment and replication. Moreover, it can also trigger immune response against viral infection in humans. This review suggested to be use the fucoidan for the potential protective remedy against COVID-19 and addressing the antiviral activities of sulfated polysaccharide, fucoidan derived from marine algae that could be used as an anti-COVID19 drug in near future.

Low-dose priming of gamma radiation enhanced cadmium tolerance in Chlamydomonas reinhardtii by modulating physio-biochemical pathways.

Microalgae are natural biotic models for exploring the genotoxic effect of heavy metals, irradiation, other external stimuli and the toxicant elimination. The effective removal of heavy metals from the aquatic environment using microalgae has gained considerable attention. However, limited research was carried out on cadmum toxicity in microalgae and their use as bio-accumulants. Previous research suggested that low-dose priming with non-ionizing radiations, such as gamma radiation, increased heavy metal tolerance in plants and aquatic photosynthetic microalgae. In the present study, we have hypothesized the growth inhibitory physiochemical properties of cadmium (Cd) in Chlamydomonas reinhardtii, and analyzed the protective role of low-dose gamma radiations priming against Cd-induced growth inhibition by emphasizing mechanism of cell survival by antioxidant defence system. Experimentally, the gamma-primed C. reinhardtii exhibited higher cell survival and Cd tolerance with effective modulation of biochemical responses such as antioxidant enzymes. The current investigation revealed that low-dose priming of gamma radiation masks Cd-mediated oxidative stress and enhances cellular detoxification via intracellular antioxidant enzymes in C. reinhardtii.

Toxic Effects and Tumor Promotion Activity of Marine Phytoplankton Toxins: A Review.

Phytoplankton are photosynthetic microorganisms in aquatic environments that produce many bioactive substances. However, some of them are toxic to aquatic organisms via filter-feeding and are even poisonous to humans through the food chain. Human poisoning from these substances and their serious long-term consequences have resulted in several health threats, including cancer, skin disorders, and other diseases, which have been frequently documented. Seafood poisoning disorders triggered by phytoplankton toxins include paralytic shellfish poisoning (PSP), neurotoxic shellfish poisoning (NSP), amnesic shellfish poisoning (ASP), diarrheic shellfish poisoning (DSP), ciguatera fish poisoning (CFP), and azaspiracid shellfish poisoning (AZP). Accordingly, identifying harmful shellfish poisoning and toxin-producing species and their detrimental effects is urgently required. Although the harmful effects of these toxins are well documented, their possible modes of action are insufficiently understood in terms of clinical symptoms. In this review, we summarize the current state of knowledge regarding phytoplankton toxins and their detrimental consequences, including tumor-promoting activity. The structure, source, and clinical symptoms caused by these toxins, as well as their molecular mechanisms of action on voltage-gated ion channels, are briefly discussed. Moreover, the possible stress-associated reactive oxygen species (ROS)-related modes of action are summarized. Finally, we describe the toxic effects of phytoplankton toxins and discuss future research in the field of stress-associated ROS-related toxicity. Moreover, these toxins can also be used in different pharmacological prospects and can be established as a potent pharmacophore in the near future.