Potential roles of hydroxybenzoate paralytic shellfish toxins in modulating toxin biokinetics in scallops.

Paralytic shellfish toxins (PSTs) produced by some marine dinoflagellates can cause severe human intoxication via vectors like bivalves. Toxic dinoflagellate Gymnodinium catenatum produce a novel group of hydroxybenzoate PSTs named GC toxins, but their biokinetics in bivalves haven't been well examined. In this experiment, we analyzed PSTs in bay scallops Argopecten irradians exposed to G. catenatum (strain MEL11) to determine their accumulation, elimination, anatomical distribution, and biotransformation. To our surprise, up to 30% of the PSTs were accumulated in the adductor muscle of scallops at the end of the experiment, and the toxicity of adductor muscle exceeded the regulatory limit of 800 µg STXeq/kg in only 6 days. High concentration of toxins in the adductor muscle are likely linked to the rapid transfer of GC toxins from viscera to other tissues. Moreover, most GC toxins in scallops were found rapidly transformed to decarbamoyl toxins through enzyme-mediated hydrolysis, which was further supported by the in vitro incubation experiments. Our study demonstrates that GC toxins actively participate in toxin distribution and transformation in scallops, which may increase the risks of food poisoning associated with the consumption of scallop adductor muscle. ENVIRONMENTAL IMPLICATION: The negative impacts of harmful algal blooms (HABs) have become a global environmental concern under the joint effects of cultural eutrophication and climate change. Our study, targeted on the biokinetics of paralytic shellfish toxins in scallops exposed to Gymnodinium catenatum producing unique GC toxins, aims to elucidate potential risks of seafood poisoning associated with GC toxins. The findings of this study will help us to understand the roles of GC toxins in seafood poisoning, and to develop effective management strategies against toxic algal blooms and phycotoxins.

An investigation on bloom dynamics of Alexandrium catenella and A. pacificum and toxin accumulation in shellfish along the coast of Qinhuangdao, China.

The dinoflagellate genus Alexandrium comprises most of the toxic bloom-forming species producing paralytic shellfish toxins (PSTs) in the sea. Recently, repeated paralytic shellfish poisoning episodes have been recorded in Qinhuangdao located at the west coast of the Bohai Sea. To elucidate the relationship between toxic Alexandrium blooms and the poisoning episodes, a year-round investigation was carried out in this region from July 2020 to July 2021. Two qPCR assays were used to detect A. catenella and A. pacificum, and LC-MS/MS was applied to analyze PSTs in phytoplankton and shellfish samples. The blooms of A. catenella and A. pacificum were found in April and July, respectively, and PST content in three bivalves exhibited notable increase following the bloom of A. catenella. The results revealed bloom dynamics of the two toxic Alexandrium species in the Bohai Sea for the first time, and further confirmed A. catenella as the causative agent of poisoning episodes.

Toxin production of dinoflagellate Gymnodinium catenatum isolated from the East China Sea.

Dinoflagellate Gymnodinium catenatum is an important producer of paralytic shellfish toxins (PSTs), including a novel group of hydroxybenzoate derivatives named GC toxins. In the East China Sea, G. catenatum has been considered as the causative agent for several paralytic shellfish poisoning (PSP) episodes, yet the knowledge on their toxin production was still quite limited. In this study, toxins produced by a strain of G. catenatum (MEL11) isolated from the East China Sea were determined, using high performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS). Changes of toxin profile in the stain MEL11 in response to nutrient and temperature variations were also examined. A total of 11 PST components dominated by hydroxybenzoate analogs and N-sulfocarbamoyl toxins were detected, which was different from other G. catenatum strains previously established in the East China Sea in the presence of GC5 and the lack of dcGTX2&3. Cellular toxin composition and content of the strain had no apparent change within a range of temperature from 20°C to 26°C. In contrast, nutrient limitation and nitrogen source had notable impacts on toxin production. The molar percentage of GC toxins decreased remarkably at the stationary growth phase under nutrient-deprived conditions of both nitrogen (N) and phosphorus (P). The replacement of nitrate with ammonium as the source of N significantly promoted PST production by G. catenatum. The study revealed the potential diversity of toxin profiles of G. catenatum in the East China Sea, and highlighted the effects of nutrients on production of GC toxins by G. catenatum.

The dinoflagellate Alexandrium catenella producing only carbamate toxins may account for the seafood poisonings in Qinhuangdao, China.

An outbreak of paralytic shellfish poisoning, recorded in April 2016 in Qinhuangdao China, was suspected to be caused by a toxic species in genus Alexandrium. Shortly after the poisoning outbreak, shellfish and net-concentrated phytoplankton samples were collected from the Bohai Sea, and analysed using high performance liquid chromatography coupled with fluorescence detection. Paralytic shellfish toxins (PSTs) were detected in both phytoplankton and shellfish samples, with similar toxin profiles dominated by carbamate toxins. High throughput sequencing data for phytoplankton samples collected previously in the coastal waters of Qinhuangdao were then analysed, and 8 operational taxonomic units (OTUs) were assigned to Alexandrium affine, A. andersonii/A. ostenfeldii, A. catenella, A. fraterculus, A. hiranoi/A. pseudogonyaulax, A. margalefii, A. pacificum and A. pohangense, among which A. catenella, A. pacificum and A. ostenfeldii could be potential producers of PSTs. During a cruise in 2019, three isolates of Alexandrium were established by cyst germination, and identified as A. catenella based on the sequences of the 28S ribosomal RNA gene (28S rDNA) D1-D2 region. Interestingly, all the three strains had the same toxin profile consisting of gonyautoxins 1, 3, 4 (GTX1, 3, 4) and neosaxitoxin (NEO). The toxin profile is similar to those of phytoplankton samples collected previously in the coastal waters of Qinhuangdao, but remarkably different from the general toxin profile of A. catenella dominated by N-sulfocarbamoyl toxins C1-2 in the Bohai Sea and the Yellow Sea. The results suggest that A. catenella is most likely to be the causative species of the poisoning outbreak in Qinhuangdao. As far as we know, this is the first report of A. catenella in the Bohai Sea producing PSTs dominated by high potent gonyautoxins GTX1-4. Occurrence of the highly toxic A. catenella will increase the risk of paralytic shellfish poisoning, which necessitates in-depth mechanism studies and increasing monitoring efforts.

Spatiotemporal variation of paralytic shellfish toxins in the sea area adjacent to the Changjiang River estuary.

The Changjiang (Yangtze River) River estuary (CRE) and its adjacent coastal waters is a notable region for nutrient pollution, which results in severe problems of coastal eutrophication and harmful algal blooms (HABs). The occurrence of HABs, particularly those of dinoflagellate Alexandrium spp. capable of producing paralytic shellfish toxins (PSTs), has an increasing risk of contaminating seafood and poisoning human-beings. The investigation of PSTs, however, is often hampered by the relatively low abundance of Alexandrium spp. present in seawater. In this study, a monitoring strategy of PSTs using net-concentrated phytoplankton from a large volume of seawater was employed to examine spatiotemporal variations of PSTs in the CRE and its adjacent waters every month from February to September in 2015. Toxins in concentrated phytoplankton samples were analyzed using high-performance liquid chromatography coupled with a fluorescence detector (HPLC-FLD). The results showed that PSTs could be detected in phytoplankton samples during the sampling stage in the CRE and its adjacent waters. Toxin content increased gradually from February to May, reached the peak in June, and then decreased rapidly from July to September. The maximum value of PST content was 215 nmol m-3 in June. Low-potency toxins N-sulfocarbamoyl toxins 1/2 (C1/2) were the most dominant components of PST in phytoplankton samples from February to June in 2015, while high-potency gonyautoxin 4 (GTX4) became the dominant component from July to September. Toxins were mainly detected from three regions, the sea area north to the CRE, the sea area east to the CRE, and sea area near Zhoushan Island south to the CRE. Based on the results of this study, it can be inferred that the three regions around the CRE in May and June is of high risk for PST contamination and seafood poisoning.