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Exposure to toxigenic harmful algal blooms (HABs) can result in widely recognized acute poisoning in humans. The five most commonly recognized HAB-related illnesses are diarrhetic shellfish poisoning (DSP), paralytic shellfish poisoning (PSP), amnesic shellfish poisoning (ASP), neurotoxic shellfish poisoning (NSP), and ciguatera poisoning (CP). Despite being caused by exposure to various toxins or toxin analogs, these clinical syndromes share numerous similarities. Humans are exposed to these toxins mainly through the consumption of fish and shellfish, which serve as the main biological vectors. However, the risk of human diseases linked to toxigenic HABs is on the rise, corresponding to a dramatic increase in the occurrence, frequency, and intensity of toxigenic HABs in coastal regions worldwide. Although a growing body of studies have focused on the toxicological assessment of HAB-related species and their toxins on aquatic organisms, the organization of this information is lacking. Consequently, a comprehensive review of the adverse effects of HAB-associated species and their toxins on those organisms could deepen our understanding of the mechanisms behind their toxic effects, which is crucial to minimizing the risks of toxigenic HABs to human and public health. To this end, this paper summarizes the effects of the five most common HAB toxins on fish, shellfish, and humans and discusses the possible mechanisms.

Background Microalgae have emerged as a potential feedstock for biofuels and bioactive components. However, lack of microalgal strains with promising triacylglycerol (TAG) content and desirable fatty acid composition have hindered its commercial feasibility. Attempts on lipid overproduction by metabolic engineering remain largely challenging in microalgae. Results In this study, a microalgal 1-acyl-sn-glycerol-3-phosphate acyltransferase designated AGPAT1 was identified in the model diatom Phaeodactylum tricornutum. AGPAT1 contained four conserved acyltransferase motifs I-IV. Subcellular localization prediction and thereafter immuno-electron microscopy revealed the localization of AGPAT1 to plastid membranes. AGPAT1 overexpression significantly altered the primary metabolism, with increased total lipid content but decreased content of total carbohydrates and soluble proteins. Intriguingly, AGPAT1 overexpression coordinated the expression of other key genes such as DGAT2 and GPAT involved in TAG synthesis, and consequently increased TAG content by 1.81-fold with a significant increase in polyunsaturated fatty acids, particularly EPA and DHA. Moreover, besides increased lipid droplets in the cytosol, ultrastructural observation showed a number of TAG-rich plastoglobuli formed in plastids. Conclusion The results suggested that AGPAT1 overexpression could elevate TAG biosynthesis and, moreover, revealed the occurrence of plastidial TAG synthesis in the diatom. Overall, our data provide a new insight into microalgal lipid metabolism and candidate target for metabolic engineering.

Background Despite the great potential of marine diatoms in biofuel sector, commercially viable biofuel production from native diatom strain is impractical. Targeted engineering of TAG pathway represents a promising approach; however, recruitment of potential candidate has been regarded as critical. Here, we identified a glycerol-3-phosphate acyltransferase 2 (GPAT2) isoform and overexpressed in Phaeodactylum tricornutum. Results GPAT2 overexpression did not impair growth and photosynthesis. GPAT2 overexpression reduced carbohydrates and protein content, however, lipid content were significantly increased. Specifically, TAG content was notably increased by 2.9-fold than phospho- and glyco-lipids. GPAT2 overexpression elicited the push-and-pull strategy by increasing the abundance of substrates for the subsequent metabolic enzymes, thereby increased the expression of LPAAT and DGAT. Besides, GPAT2-mediated lipid overproduction coordinated the expression of NADPH biosynthetic genes. GPAT2 altered the fatty acid profile in TAGs with C16:0 as the predominant fatty acid moieties. We further investigated the impact of GPAT2 on conferring abiotic stress, which exhibited enhanced tolerance to hyposaline (70%) and chilling (10 ºC) conditions via altered fatty acid saturation level. Conclusions Collectively, our results exemplified the critical role of GPAT2 in hyperaccumulating TAGs with altered fatty acid profile, which in turn uphold resistance to abiotic stress conditions.

Background The marine diatom, Phaeodactylum tricornutum, has become a model for studying lipid metabolism and its triacylglycerol (TAG) synthesis pathway makes it an ideal target for metabolic engineering to improve lipid productivity. However, the genetic background and metabolic networks of fatty acid biosynthesis in diatoms are not well understood. Glycerol-3-phosphate acyltransferase (GPAT) is the critical enzyme that catalyzes the first step of TAG formation. So far, characterization of GPAT in marine microalgae has not been reported, especially at the level of comprehensive sequence-structure and functional analysis. Results A GPAT was cloned from P. tricornutum and overexpressed in P. tricornutum. Volumes of oil bodies were produced and the neutral lipid content was increased by twofold determined by Nile red fluorescence staining. Fatty acid composition was analyzed by GC-MS, which showed significantly higher proportion of unsaturated fatty acids compared to wild type. Conclusion These results suggested that the identified GPAT could upregulate TAG biosynthesis in P. tricornutum. Moreover, this study offers insight into the lipid metabolism of diatoms and supports the role of microalgal strains for biofuels production.

Diatoms are a crucial component of marine ecosystems, recognized for their broad environmental adaptability and wide temperature tolerance. However, the molecular mechanisms underlying their adaptability to diverse temperatures are unknown. In this study, we discover that heat shock transcription factors (HSFs) are potentially important for thermal tolerance in diatoms. Our study focuses on PtHSF2, annotated as HSF2 in Phaeodactylum tricornutum ’s genome, which is ubiquitous in diatoms. Overexpression of PtHSF2 markedly enhances thermal tolerance and increases cell size; causes significant differential expression of several genes, including cell division cycle protein 45-like ( PtCdc45-like ), ATM (ataxia telangiectasia mutated), ATR (ataxia telangiectasia and Rad3-related), light-harvesting complex protein 2 ( Lhcx2 ), and fatty acid desaturase. Cleavage Under Targets and Tagmentation (CUT&Tag) and CUT&Tag-qPCR analyses demonstrate that PtHSF2 directly targets and upregulates PtCdc45-like and Lhcx2 while downregulating ATP-binding cassette transporter. Functional validation of PtCdc45-like shows that its overexpression results in larger cell size, enhances antioxidant capacity, and improves cell survival at elevated temperatures. Collectively, our findings elucidate the molecular mechanism by which PtHSF2 mediates high-temperature tolerance in diatoms and validate the functions of its target gene PtCdc45-like . These results highlight the importance of HSFs in diatom temperature adaptation and provide insights into temperature acclimation in microalgae. Diatoms are crucial marine microorganisms, but the molecular mechanisms underlying their temperature tolerance remain unclear. This study identifies the heat shock transcription factor PtHSF2 as a key regulator of thermal tolerance and cell size plasticity in Phaeodactylum tricornutum, revealing its role in gene regulation and stress response.

Microalgae have been emerging as an important source for the production of bioactive compounds. Marine diatoms can store high amounts of lipid and grow quite quickly. However, the genetic and biochemical characteristics of fatty acid biosynthesis in diatoms remain unclear. Glycerophospholipids are integral as structural and functional components of cellular membranes, as well as precursors of various lipid mediators. In addition, diacylglycerol acyltransferase (DGAT) is a key enzyme that catalyzes the last step of triacylglyceride (TAG) biosynthesis. However, a comprehensive sequence-structure and functional analysis of DGAT in diatoms is lacking. In this study, an isoform of diacylglycerol acyltransferase type 2 of the marine diatom Phaeodactylum tricornutum was characterized. Surprisingly, DGAT2 overexpression in P. tricornutum stimulated more oil bodies, and the neutral lipid content increased by 35%. The fatty acid composition showed a significant increase in the proportion of polyunsaturated fatty acids; in particular, EPA was increased by 76.2%. Moreover, the growth rate of transgenic microalgae remained similar, thereby maintaining a high biomass. Our results suggest that increased DGAT2 expression could alter fatty acid profile in the diatom, and the results thus represent a valuable strategy for polyunsaturated fatty acid production by genetic manipulation.

Background Conus , a highly diverse species of venomous predators, has attracted significant attention in neuroscience and new drug development due to their rich collection of neuroactive peptides called conotoxins. Recent advancements in transcriptome, proteome, and genome analyses have facilitated the identification of conotoxins within Conus ’ venom glands, providing insights into the genetic features and evolutionary patterns of conotoxin genes. However, the underlying mechanism behind the extraordinary hypervariability of conotoxins remains largely unknown. Results We analyzed the transcriptomes of 34 Conus species, examining various tissues such as the venom duct, venom bulb, and salivary gland, leading to the identification of conotoxin genes. Genetic variation analysis revealed that a subset of these genes (15.78% of the total) in Conus species underwent positive selection (Ka/Ks > 1, p  < 0.01). Additionally, we reassembled and annotated the genome of C. betulinus , uncovering 221 conotoxin-encoding genes. These genes primarily consisted of three exons, with a significant portion showing high transcriptional activity in the venom ducts. Importantly, the flanking regions and adjacent introns of conotoxin genes exhibited a higher prevalence of transposon elements, suggesting their potential contribution to the extensive variability observed in conotoxins. Furthermore, we detected genome duplication in C. betulinus , which likely contributed to the expansion of conotoxin gene numbers. Interestingly, our study also provided evidence of introgression among Conus species, indicating that interspecies hybridization may have played a role in shaping the evolution of diverse conotoxin genes. Conclusions This study highlights the impact of adaptive evolution and introgressive hybridization on the genetic diversity of conotoxin genes and the evolution of Conus . We also propose a hypothesis suggesting that transposable elements might significantly contribute to the remarkable diversity observed in conotoxins. These findings not only enhance our understanding of peptide genetic diversity but also present a novel approach for peptide bioengineering.

Marine bivalves are rich in docosahexaenoic acid (DHA), a polyunsaturated fatty acid known to be beneficial for human health; however, the potential role of DHA in protecting shellfish from the toxicity of diarrhetic shellfish toxins (DSTs) remains poorly understood. Here, we aimed to study the effect of DHA on the response of the bivalve, Perna viridis, to DSTs by using LC-MS/MS, RT-qPCR, and histological examination. In this study, we observed that the DHA content decreased significantly with esterification of DSTs in the digestive gland of the mussel P. viridis after 96 h of exposure to Prorocentrum lima, a DST-producing dinoflagellate. The addition of DHA significantly increased the esterification level of DSTs and increased the expression of Nrf2 signaling pathway-related genes and enzyme activities, alleviating the damage of DSTs to digestive glands. These results suggested that DHA may mediate the esterification of DSTs and activation of the Nrf2 signaling pathway in P. viridis to protect mussels from the toxic effects of DSTs. This study may provide new insights regarding the response of bivalves to DSTs and lay the foundation for uncovering the role of DHA in environmental adaptation of bivalves.

Furochromones are specific bioactive secondary metabolites of many Apiaceae plants. Their biosynthesis remains largely unexplored. In this work, we dissect the complete biosynthetic pathway of major furochromones in the medicinal plant Saposhnikovia divaricata by characterizing prenyltransferase, peucenin cyclase, methyltransferase, hydroxylase, and glycosyltransferases. De novo biosynthesis of prim- O -glucosylcimifugin and 5- O -methylvisamminoside is realized in Nicotiana benthamiana leaves. Through comparative genomic and transcriptomic analyses, we further find that proximal duplication and high expression of a pentaketide chromone synthase gene SdPCS , together with the presence of a lineage-specific peucenin cyclase gene SdPC , lead to the predominant accumulation of furochromones in the roots of S. divaricata among surveyed Apiaceae plants. This study paves the way for metabolic engineering production of furochromones, and sheds light into evolutionary mechanisms of furochromone biosynthesis among Apiaceae plants. The complete biosynthetic pathway of Prim- O -Glucosylcimifugin and 5- O -Methylvisamminoside in Saposhnikovia divaricata is resolved and their de novo biosynthesis is reconstructed in Nicotiana benthamiana leaves. The evolutionary mechanisms of furochromone biosynthesis among Apiaceae plants is further analyzed.

As emerging contaminants, microplastics (MPs) may pose a threat to human health. Their co-exposure with the widespread phycotoxin okadaic acid (OA), a marine toxin known to cause gastrointestinal toxicity, may exacerbate health risk and raise public safety concern. In this study, the toxicity mechanisms of MPs and OA on intestinal microenvironment was explored using human Caco-2 cells as the model, which was combined with an in vitro fecal fermentation experiment. Our results showed that co-exposure to MPs (80 μg/mL) and OA (20 ng/mL) significantly decreased cell viability, increased intracellular reactive oxygen species (ROS) production, elevated lactate dehydrogenase release, impaired ABC transporter activity, promoted OA accumulation, and triggered inflammatory response compared to the control, MPs, and OA groups, indicating that co-exposure directly compromises intestinal epithelial integrity. In vitro fermentation experiments revealed that co-exposure disrupted gut microbial composition, decreasing the relative abundance of some bacteria, such as Parasutterella and Adlercreutzia, while increasing opportunistic pathogens, such as Escherichia-Shigella, increased. These findings provide new insights into the impact and underlying mechanisms of MPs and OA co-exposure on intestinal homeostasis, highlighting the potential health risks associated with MPs.