Conversion of Retinoids along the Marine Food Chain Contributes to Adverse Impacts on the Spine, Liver, and Intestinal Health of the Marine Medaka (Oryzias melastigma).

Marine microalgae serve as an aquaculture bait. To enhance algal cell growth and breeding profits, high-intensity light conditions are standard for cultivating bait microalgae, potentially altering microalgal metabolite production. This research revealed that Thalassiosira pseudonana, when subjected to high-intensity light conditions, accumulated significant quantities of retinal (RAL) that transferred through the food chain and transformed into all-trans retinoic acid (atRA) in marine medaka. The study further explored the toxic effects on individual fish and specific tissues, as well as the mechanisms behind this toxicity. The accumulation of atRA in the liver, intestine, and spinal column resulted in structural damage and tissue inflammation, as well as oxidative stress. It also down-regulated the gene transcription levels of key pathways involved in immune function and growth. Furthermore, it disrupted the homeostasis of the intestinal microbial communities. The implications for wildlife and human health, which are influenced by the regulation of microalgal metabolite accumulation and their transfer via the food chain, require further investigation and could hold broader significance.

Five Karenia species along the Chinese coast: With the description of a new species, Karenia hui sp. nov. (Kareniaceae, Dinophyta).

Dinoflagellates within the genus Karenia are well known for their potential to cause harmful algal blooms and induce detrimental ecological consequences. In this study, five Karenia species, Karenia longicanalis, Karenia papilionacea, Karenia mikimotoi, Karenia selliformis, and a new species, Karenia hui sp. nov., were isolated from Chinese coastal waters. The new species exhibits the typical characteristics of the genus Karenia, including a linear apical groove and butanoyl-oxyfucoxanthin as the major accessory pigment. It is distinguished from the other Karenia species by a wide-open sulcal intrusion onto the epicone, a conical epicone with an apical crest formed by the rim of the apical groove, and a hunchbacked hypocone. It is most closely related to Karenia cristata, with a genetic divergence of 3.16 % (22 bp out of 883 bp of LSU rDNA). Acute toxicity tests indicated that the five Karenia species from China are all toxic to marine medaka Oryzias melastigma. Karenia selliformis and K. hui were very toxic to O. melastigma, resulting in 100 % mortality within 4 h and 24 h, respectively. Further analysis by high-performance liquid chromatography revealed that four species, K. selliformis, K. longicanalis, K. papilionacea and K. mikimotoi were capable of producing Gymnodimine-A (GYM-A). The highest GYM-A content was in K. selliformis (strain HK-43), in which the value was 889 fg/cell. No GYM-A was detected in the new species K. hui, however and its toxin remains unknown. Below we provide a comprehensive report of the morphology, phylogeny, pigment composition, and toxicity profiles of Karenia species along the Chinese coast. These findings contribute new insights for monitoring of Karenia species, with important toxicological and ecological implications.

Refining taxonomic identification of microalgae through molecular and genetic evolution: a case study of Prorocentrum lima and Prorocentrum arenarium.

Species delimitation based on lineage definition has become increasingly popular. However, these methods have been limited, especially for species that lack genomic data and are morphologically similar. The trickiest part for the species identification is that the interspecific and intraspecific boundaries are vague. Taking Prorocentrum (Dinophyta) as an example, analysis of cell morphology, growth, and toxin synthesis in both species of P. lima and P. arenarium does not provide a reliable basis for species delineation. However, through phylogenetic and genetic distance analyses of their ITS and LSU sequences, establishment of evolutionary tree based on orthologous gene sequences, and combining the results of automatic barcode gap discovery and Poisson tree processes models, it was sustained that P. arenarium does not belong to the P. lima complex and should be considered as an independent species. Interspecies genetic evolution analysis revealed that P. lima and P. arenarium may contribute to evolutionary direction that favors combating reverse environmental factors. In P. lima, viral invasion may be one of the reasons for its large genome size. In the study, P. lima complex has been selected as an example to enhance the taxonomic identification of microalgae through molecular and genetic evolution, offering valuable insights into refining taxonomic identification and promoting microbial biodiversity research in other species.IMPORTANCEMicroalgae, especially the species known as Prorocentrum, have received significant attention due to their ability to trigger harmful algal blooms and produce toxins. However, the boundaries between species and within species are ambiguous. Clear and comprehensive species delineation indicates that Prorocentrum arenarium should be considered as an independent species, separate from the Prorocentrum lima complex. Improving the classification and identification of microalgae through molecular and genetic evolution will provide reference points for other cryptic species. Prorocentrum occupy multiple ecological niches in marine environments, and studying their evolutionary direction contributes to understanding their ecological adaptations and community succession.

Prediction of Aureococcus anophageffens using machine learning and deep learning.

The recurrent brown tide phenomenon, attributed to Aureococcus anophagefferens (A. anophagefferens), constitutes a significant threat to the Qinhuangdao sea area in China, leading to pronounced ecological degradation and substantial economic losses. This study utilized machine learning and deep learning techniques to predict A. anophagefferens population density, aiming to elucidate the occurrence mechanism and influencing factors of brown tide. Specifically, Random Forest (RF) algorithm was utilized to impute missing water quality data, facilitating its direct application in subsequent algal population prediction models. The results revealed that all four models-RF, Support Vector Regression (SVR), Multilayer Perceptron (MLP), and Convolutional Neural Network (CNN)-exhibited high accuracy in predicting A. anophagefferens population densities, with R2 values exceeding 0.75. RF, in particular, showed exceptional accuracy and reliability, with an R2 value surpassing 0.8. Additionally, the study ascertained five critical factors influencing A. anophagefferens population density: ammonia nitrogen, pH, total nitrogen, temperature, and silicate.

RA-induced prominence-specific response resulted in distinctive regulation of Wnt and osteogenesis.

Proper retinoic acid (RA) signaling is essential for normal craniofacial development. Both excessive RA and RA deficiency in early embryonic stage may lead to a variety of craniofacial malformations, for example, cleft palate, which have been investigated extensively. Dysregulated Wnt and Shh signaling were shown to underlie the pathogenesis of RA-induced craniofacial defects. In our present study, we showed a spatiotemporal-specific effect of RA signaling in regulating early development of facial prominences. Although inhibited Wnt activities was observed in E12.5/E13.5 mouse palatal shelves, early exposure of excessive RA induced Wnt signaling and Wnt-related gene expression in E11.5/E12.5 mouse embryonic frontonasal/maxillary processes. A conserved regulatory network of miR-484-Fzd5 was identified to play critical roles in RA-regulated craniofacial development using RNA-seq. In addition, subsequent osteogenic/chondrogenic differentiation were differentially regulated in discrete mouse embryonic facial prominences in response to early RA induction, demonstrated using both in vitro and in vivo analyses.

Adaptive responses of geographically distinct strains of the benthic dinoflagellate, Prorocentrum lima (Dinophyceae), to varying light intensity and photoperiod.

The toxic Prorocentrum lima complex can potentially cause serious harm to the benthos and entire food chain. Studies have revealed physiological differences in strains from different regions related to local environment, while differences in the adaptive responses of P. lima complex should be urgently assessed. Hence, this study explored the adaptive responses to varying light intensities and photoperiods of two P. lima complex strains SHG101 and 3XS34, isolated from the Bohai Sea and the South China Sea, respectively. We found the highest cell density of 7.49 × 104 cells mL-1 recorded in the 3XS strain in the stationary phase with high light intensity exposure. No significant difference was observed in growth rate among SHG groups, however, significant differences were found among 3XS groups ranging from 0.176 to 0.311 d-1. Three key pigments Chl a, Peri, and Fuco accounted for up to 60% of the total pigments. Production and concentrations of pigments and Fv/Fm values exhibit a significant negative correlation with high light intensity and growth. Conversely, total diarrhetic shellfish toxin content and the proportion of diol esters increased to varying degrees after high intensity light exposure, with 3XS strain under high light intensity and a photoperiod of light and darkness (12L:12D) consistently exhibiting the highest levels, finally reaching a maximum (21.6 pg cell-1) at day 28. A shortened photoperiod of high light intensity (8L:16D) resulted in impaired recovery compared with 12L:12D. Furthermore, 3XS showed more delayed and intense adaptive responses, indicating a stronger tolerance compared to SHG. Collectively, these results directly characterized variation in the adaptive responses of geographically distinct strains of P. lima complex, highlighting the previously ignored potential risk diversity of this species.

Sublethal effects on the hard clam Mercenaria mercenaria after exposure to Aureococcus anophagefferens Chinese strain isolates.

Brown tides caused by Aureococcus anophagefferens occur frequently worldwide and have contributed to the collapse of Mercenaria mercenaria farming in the United States. This economically valuable hard clam has been used in China for more than 20 years. To date, it has remained unknown whether A. anophagefferens Chinese strain has an impact on hard clam cultivation in the coastal areas of China or other sea areas worldwide if it enters through ship ballast water and other ways. In this study, a Chinese strain of A. anophagefferens isolated from the brown tide waters of Bohai Bay, China, was selected to explore its influence on the feedback of hard clams. After being fed with A. anophagefferens, hard clams showed characteristics similar to starvation. The reduced feeding efficiency of hard clams leads to reduced energy intake. However, the immune response and oxidative stress, result in increased energy consumption. An imbalance in the energy budget may be an important reason for hard clam starvation. This study has described the response characteristics of the A. anophagefferens Chinese strain to M. mercenaria, explored the reasons for the negative impact of A. anophagefferens on hard clams, and provides ideas for reducing shellfish aquaculture caused by brown tides.

Phytoplankton community and HAB species in the South China Sea detected by morphological and metabarcoding approaches.

The southern Chinese coast is one of the most developed regions in China and is an area where harmful algal blooms (HABs) have occurred frequently. In this study, differences in the phytoplankton community between microscopic observations and 18S rDNA metabarcoding were compared in 89 surface water samples collected from the southern Chinese coast and the western South China Sea (SCS). This is the first report investigating the phytoplankton community and HAB species using a combination of morphological and metabarcoding approaches in this sea area. There were substantial differences in phytoplankton community structure detected by the two methods. Microscopic observation revealed diatom predominance in the phytoplankton community, while metabarcoding indicated dinoflagellate dominance. The phytoplankton community structure obtained by microscopic observation better reflects the real situation in the water column. Metabarcoding annotated more species than morphospecies observed by microscopy. Haptophyta and Cryptophyta were the specific phyla detected in metabarcoding but were missed in microscopy due to their small size. Conversely, some taxa were found in microscopic analysis alone, such as species in Dinophysis, Prorocentrum, and Scrippsiella, suggesting some biases during metabarcoding and gaps in sequence databases. Metabarcoding is superior for detecting morphologically cryptic, small-sized and HAB taxa, such as unarmored dinoflagellates, nanosized hatophytes and chlorophytes, as well as multiple species in Alexandrium, Pseudonitzschia, and Chaetoceros in our study. A total of 62 HAB taxa were identified in this study, including blooming and potentially toxic species. Diatom abundances generally decreased southward, while those of dinoflagellates and haptophytes showed the opposite trend. Chlorophytes were mainly distributed in coastal waters, especially in the Pearl River Estuary. Phytoplankton community structures were shaped by nutrients and salinity, and phosphorus was the most limiting factor for phytoplankton growth. The phytoplankton community in the western SCS showed unique characteristics away from those in the coastal sea areas. The results suggest that the combination of morphological and metabarcoding approaches comprehensively reveals the phytoplankton community structure and diversity of HAB species.

An overview of Prorocentrum donghaiense blooms in China: Species identification, occurrences, ecological consequences, and factors regulating prevalence.

Prorocentrum donghaiense Lu (also identified as Prorocentrum shikokuense Hada and Prorocentrum obtusidens Schiller) is a bloom-forming dinoflagellate species distributed worldwide. Blooms of P. donghaiense occur annually in adjacent waters of the East China Sea (ECS), especially in the waters near the Changjiang River Estuary. Blooms of this species have also been reported in nearby Japanese and Korean waters. There has been an apparent bloom-forming species succession pattern in the ECS since 2000, with diatom blooms in the early spring, shifting to long-lasting and large-scale dinoflagellate blooms dominated by P. donghaiense during the spring, and finally ended by diatom and/or Noctiluca scintillans blooms in summer. These bloom succession patterns were closely correlated with changes in environmental factors, such as temperature increase and anthropogenic eutrophication. Decreasing silicate by the construction of the Three Gorges Dam and increasing dissolved inorganic nitrogen flux were mainly influenced by high intensity human activities in the Changjiang River watershed, resulting in low Si/N ratio and high N/P ratios, possibly accelerating outbreak of P. donghaiense blooms. Phosphorous deficiency might be the most critical factor controlling the succession of microalgal blooms from diatoms to dinoflagellates. Prorocentrum donghaiense is a nontoxic species, but it can disrupt marine ecosystem by decreasing phytoplankton biodiversity and changing the structure of the food chain. Prorocentrum donghaiense blooms in the ECS have been intensively studied during the last two decades. Several possible mechanisms that contribute or trigger the annual blooms of this species have been proposed, but further research is required particularly on the aspect of nutrient budget, ecosystem impacts, as well as social-economic impact assessment.

Emerging harmful algal bloom species over the last four decades in China.

The first recorded micro-algae bloom in Chinese coastal waters dates back to 1933 and was caused by a mixture of Noctiluca scintillans and Skeletonema costatum sensu lato along the Zhejiang coast (the East China Sea). While well-documented harmful algal blooms (HABs) appeared to be extremely scarce from the 1950s to 1990, both the frequency and intensity have been reportedly increasing since 1990. Among them, the fish-killing HABs, mainly caused by Karenia mikimotoi, Karlodinium digitatum, Karlodinium veneficum, Margalefidinium polykrikoides, and Heterocapsa spp., have intensified. Karenia mikimotoi was responsible for at least two extremely serious events in the Pearl River Estuary in 1998 and the Taiwan Strait (in the East China Sea) in 2012, which appeared to be associated with abnormal climate conditions and excessive nutrients loading. Other major toxic algal blooms have been caused by the species responsible for paralytic shellfish poisoning (including Alexandrium catenella, Alexandrium pacificum, Gymnodinium catenatum) and diarrhetic shellfish poisoning (including Dinophysis spp., and a couple of benthic dinoflagellates). Consequent closures of shellfish farms have resulted in enormous economic losses, while consumption of contaminated shellfish has led to occasional human mortality in the Bohai Sea and the East China Sea. Expansions of these HABs species along the coastline of China have occurred over the last four decades and, due to the projected global changes in the climate and marine environments and other anthropological activities, there is potential for the emergence of new types of HABs in China in the future. This literature review aimed to present an updated overview of HABs species over the last four decades in China.

Bioavailability of Organic Phosphorus Compounds to the Harmful Dinoflagellate Karenia mikimotoi.

Karenia mikimotoi is one of the most well-known harmful bloom species in temperate coastal waters. The present study investigated the characteristics of alkaline phosphatase (APase) and phosphodiesterase (PDEase) activities in hydrolysis of two phosphomonoesters (adenosine triphosphate (ATP) and ribulose 5-phosphate (R5P)) and a phosphodiester (cyclic adenosine monophosphate (cAMP)) in K. mikimotoi and compared its growth and physiological responses to the different forms of phosphorus substrates. K. mikimotoi produced comparable quantities of APase and PDEase to hydrolyze the organic phosphorus substrates, although hydrolysis of the phosphomonoesters was much faster than that of the phosphodiester. The growth of K. mikimotoi on organic phosphorus substrates was comparable to or better than that on inorganic phosphate. The difference in particulate organic nutrients (carbon, nitrogen, and phosphorus) and hemolytic activity supported different rates of hydrolysis-assimilation of the various organic phosphorus substrates by K. mikimotoi. The hemolytic activities of K. mikimotoi in the presence of organic phosphorus substrates were several times those in the presence of inorganic phosphate during the exponential phase. This suggested the potential important role of organic phosphorus in K. mikimotoi blooms.

The harmful raphidophyte Chattonella (Raphidophyceae) in Western Pacific: Its red tides and associated fisheries damage over the past 50 years (1969-2019).

Red tides and associated fisheries damage caused by the harmful raphidophyte Chattonella were reassessed based on the documented local records for 50 years to understand the distribution and economic impacts of the harmful species in the Western Pacific. Blooms of Chattonella with fisheries damage have been recorded in East Asia since 1969, whereas they have been only recorded in Southeast Asia since the 1980s. Occurrences of Chattonella have been documented from six Southeast Asian countries, Indonesia, Malaysia, Philippines, Singapore, Thailand and Viet Nam, with mass mortalities mainly of farmed shrimp in 1980-1990s, and farmed fish in 2000-2010s. These occurrences have been reported with the names of C. antiqua, C. marina, C. ovata, C. subsalsa and Chattonella sp., owing to the difficulty of microscopic species identification, and many were not supported with molecular data. To determine the distribution of C. marina complex and C. subsalsa in Southeast Asia, molecular phylogeny and microscopic observation were also carried out for cultures obtained from Indonesia, Malaysia, Japan, Philippines, Russia, Singapore and Thailand. The results revealed that only the genotype of C. marina complex has been detected from East Asia (China, Japan, Korea and Russia), whereas both C. marina complex (Indonesia and Malaysia) and C. subsalsa (Philippines, Singapore and Thailand) were found in Southeast Asia. Ejection of mucocysts has been recognized as a diagnostic character of C. subsalsa, but it was also observed in our cultures of C. marina isolated from Indonesia, Malaysia, Japan, and Russia. Meanwhile, the co-occurrences of the two harmful Chattonella species in Southeast Asia, which are difficult to distinguish solely based on their morphology, suggest the importance of molecular identification of Chattonella genotypes for further understanding of their distribution and negative impacts.

Effects of Prorocentrum donghaiense bloom on zooplankton functional groups in the coastal waters of the East China Sea.

Blooms of the non-toxic dinoflagellate Prorocentrum donghaiense are common in the East China Sea; however, the in situ impacts of these blooms on zooplankton community functions have not yet been conducted in this area. Using functional trait-based methods, we found that P. donghaiense bloom significantly changed the zooplankton community structure and functions in the coastal water of the East China Sea. Zooplankton species richness and biodiversity increased after the bloom. Based on body length, feeding type, trophic group and reproductive mode, we categorized zooplankton into four functional groups and characterized their dynamics. Before and after the bloom, the zooplankton community was dominated by herbivorous- and free-spawner- lineages represented by copepods and tunicates, while during the bloom, the zooplankton community was dominated by carnivorous- and egg-brooding- lineages represented by small jellyfish, chaetognaths and copepods.

Effects of temperature on the growth and carbohydrate production of three benthic dinoflagellate species from Hainan Island, South China Sea.

Dinoflagellates in the genera Ostreopsis and Gambierdiscus are typical members of the marine benthic community particularly in tropical areas. Their geographic distribution has shown an increasing expansion towards temperate waters recently due to the global warming and climate changes; however, the knowledge is little of how the increasing temperatures might influence the physiological characteristics of Ostreopsis spp. and Gambierdiscus spp. Here, we carried out experiments to understand the effect of different temperatures on the growth, chlorophyll a content, and carbohydrate yield of Chinese strains of Ostreopsis cf. ovata, O. lenticularis, and Gambierdiscus caribaeus. Specifically, seven temperatures (15, 17.5, 20, 25, 30, 32.5, and 35 °C) were set for the two Ostreopsis species and five temperatures (15, 20, 25, 30, and 35 °C) were set for G. caribaeus. Our results suggested that both Ostreopsis (both species were 17.5-32.5 °C) and Gambierdiscus (20-35 °C) could survive a wide range of temperatures, consistent with the record worldwide. Cell density and chlorophyll a content were observed to be higher at high temperatures (30 and 32.5 °C) for both Ostreopsis species whereas G. caribaeus reached the maximum cell density and highest growth rate at 20 °C. Higher carbohydrate yield was detected in the suboptimal temperatures for all three dinoflagellates especially during the decaying phase. Our study reveals the optimal temperatures for the growth of three benthic harmful dinoflagellate species and provides insight into how the increasing temperature will affect their abundance as well as distribution.

Phytoplankton community organization and succession by sea warming: A case study in thermal discharge area of the northern coastal seawater of China.

Thermal discharges from power plants elevate temperatures in the surrounding waters, and this warming of the marine environment inevitably influences phytoplankton communities. In this study, we conducted seasonal sampling in coastal waters of the Bohai Sea off Qinhuangdao, China. The results revealed that the coastal waters are notably affected by thermal discharge, with unseasonably-high water temperatures, particularly during winter. The change of phytoplankton community structure has been detected in the warmer coastal seawater. Although diatoms were the dominant species during field investigations, there were no significant seasonal changes in diatom abundance. In contrast, the density of dinoflagellates was low in all seasons due to the effects of thermal discharge. Consequently, the general trend in phytoplankton succession was interrupted. In general, the findings of this study may provide further insights into the warmer environmental impacts on phytoplankton communities in temperate regions.

Autoactivation of Translation Causes the Bloom of Prorocentrum donghaiense in Harmful Algal Blooms.

Harmful algal blooms (HABs) are symptomatic of ecosystem imbalance, leading to major worldwide marine natural disasters, and seriously threaten the human health. Some HAB algae's exceptional genome size prohibited the genomic investigations on molecular mechanisms, for example, Prorocentrum. This study performed translatome sequencing (RNC-seq) for Prorocentrum donghaiense to assemble the translatome reference sequences on appropriate cost to enable the global molecular study at translatome and proteome levels. By analyzing the translatome and proteome of P. donghaiense in phosphor-rich, phosphor-deficient, and phosphor-restored media, we found massive up-regulation of energy and material production pathways in phosphor-rich conditions that enables autoactivation of translation, which is the key to its exponential growth in HABs. To break down the autoactivation, we demonstrated that mild translation delay using very low concentrations of cycloheximide efficiently controls the blooming without harming other aquatic organisms and humans. Our result provides a novel hint for controlling HABs and demonstrated the RNC-seq as an economic strategy on investigating functions of organisms with large and unknown genomes.

Alkaline phosphatase activity during a phosphate replete dinoflagellate bloom caused by Prorocentrum obtusidens.

Prorocentrum obtusidens Schiller (formerly P. donghaiense Lu), a harmful algal species common in the East China Sea (ECS), often thrives with the depletion of phosphate. Three cruises in the spring of 2013 sampled an entire P. obtusidens bloom process to investigate the dynamics of alkaline phosphatase activity (APA) and phosphorus (P) status of the bloom species using both bulk and cell-specific assays. Unlike previous studies, the bloom of P. obtusidens occurred in a phosphate replete environment. Very high APA, with an average of 76.62 ± 90.24 nmol L-1 h-1, was observed during the early-bloom phase, a value comparable to that in low phosphate environments. The alkaline phosphatase (AP) hydrolytic kinetics also suggested a more efficient AP system with a lower half-saturation constant (Ks), but higher maximum potential hydrolytic velocity (Vmax) in this period. The APA decreased significantly with an average of 24.98 ± 30.98 nmol L-1 h-1 when the bloom reached its peak. The lack of a correlation between dissolved inorganic phosphate (DIP) or dissolved organic phosphate (DOP) concentration and APA suggested that the APA was regulated by the internal P growth demand, rather than the external P availability during the phosphate replete P. obtusidens bloom. These findings facilitate an understanding of the P. obtusidens acclimation strategy with respect to P variations in terms of AP expression during blooms in the ECS.

Photocatalytic inactivation and destruction of harmful microalgae Karenia mikimotoi under visible-light irradiation: Insights into physiological response and toxicity assessment.

Harmful algal blooms (HABs) caused by Karenia mikimotoi have frequently happened in coastal waters worldwide, causing serious damages to marine ecosystems and economic losses. Photocatalysis has potential to in-situ inhibit algal growth using sustainable sunlight. However, the inactivation and detoxification mechanisms of microalgae in marine environment have not been systematically investigated. In this work, for the first time, visible-light-driven photocatalytic inactivation of K. mikimotoi was attempted using g-C3N4/TiO2 immobilized films as a model photocatalyst. The inactivation efficiency could reach 64% within 60 min, evaluated by real-time in vivo chlorophyll-a fluorometric method. The immobilized photocatalyst films also exhibited excellent photo-stability and recyclability. Mechanisms study indicated photo-generated h+ and 1O2 were the dominant reactive species. Algal cell rupture process was monitored by fluorescent microscope combined with SEM observation, which confirmed the damage of cell membrane followed by the leakage of the intracellular components including the entire cell nucleus. The physiological responses regarding up-regulation of antioxidant enzyme activity (i.e. CAT and SOD), intracellular ROSs level and lipid peroxidation were all observed. Moreover, the intracellular release profile and acute toxicity assessment indicated the toxic K. mikimotoi was successfully detoxified, and the released organic matter had no cytotoxicity. This work not only provides a potential new strategy for in-situ treatment of K. mikimotoi using sunlight at sea environments, but also creates avenue for understanding the inactivation and destruction mechanisms of marine microalgae treated by photocatalysis and the toxicity impacts on the marine environments.

Identifying the Source Organisms Producing Paralytic Shellfish Toxins in a Subtropical Bay in the South China Sea.

Identifying the exact phytoplanktonic sources of paralytic shellfish toxins (PSTs) is crucial for monitoring and preventing the buildup of toxin pollution, especially for causative species occurring at low levels. Phytoplankton and shellfish samples were simultaneously collected from representative mariculture zones in Daya Bay, China. Low concentration/low toxicity PSTs predominated with N-sulfocarbamoyl toxins 1, 2 (C1/2) being detected in phytoplankton (≤6.25 pmol L-1) and shellfish (≤0.21 µg STXeq g-1), which pose a potential risk of seafood poisoning. High-throughput sequencing of the phytoplankton samples based on 18S rDNA V4 regions identified 93 genera in 445 operational taxonomic units (OTUs). Five OTUs were assigned to Alexandrium hiranoi, Ambicodamus leei, Alexandrium pacificum, Alexandrium minutum, and an uncertain Alexandrium sp. A. pacificum and A. minutum are candidate PST producers and observed under the light microscope with densities of 66-972 cells L-1. Three strains of toxigenic species were successfully isolated and identified as A. pacificum and A. minutum based on their 18S rDNA V4 regions. The predominant toxins in A. pacificum were C1/2 (43.9-53.6 fmol cell-1) and resembled the toxins found in field samples predominated with C1/2. A. minutum produced only gonyautoxins 2/3 (8.03 fmol cell-1). Therefore, A. pacificum was identified as the predominant PST contributor in this area. This research makes a valuable contribution to the understanding of the traceability of phycotoxins in marine waters.

Effects of triclosan on the RedoximiRs/Sirtuin/Nrf2/ARE signaling pathway in mosquitofish (Gambusia affinis).

Triclosan (TCS) has been widely used in daily life for its broad-spectrum antibacterial property and subsequently detected frequently in aquatic waterborne. Environmental relevant concentrations of TCS in water (ng-µg/L) may pose potential unexpected impact on non-target aquatic organisms. In the present work, we investigated the transcriptional responses of Nrf2 as well as its downstream genes, sirtuins and redox-sensitive microRNAs (RedoximiRs) in livers of the small freshwater fish mosquitofish (Gambusia affinis) which were exposed to environmental relevant concentrations of TCS (0.05 µg/L, 0.5 µg/L and 5 µg/L for 24 h and 168 h). Results showed there were similar up-regulations in Nrf2 and its target genes (e. g. NQO1, CAT and SOD) at transcriptional, enzymatic and protein levels, reflecting oxidative stress of TCS to mosquitofish. Meanwhile, up-regulations of Sirt1, Sirt2 and down-regulations of miR-34b, miR-200b-5p and miR-21 could modulate antioxidant system via the Nrf2/ARE signaling pathway by the post-transcriptional regulations. Some oxidative stress-related biomarkers displayed in concentration-dependent manners (e. g. NQO1 mRNA, CAT mRNA) and/or time-dependent manners (e. g. GSH contents). This study indicated that the RedoximiRs/Sirtuin/Nrf2/ARE signaling pathway played a crucial role in mosquitofish exposed to TCS, and there might be potentially profound effects for TCS on the aquatic ecological safety.