Characterization of toxin-producing strains of Dinophysis spp. (Dinophyceae) isolated from French coastal waters, with a particular focus on the D. acuminata-complex

Marine phycotoxin levels in shellfish-14 years of data gathered along the Italian coast

Along the Italian coasts, toxins of algal origin in wild and cultivated shellfish have been reported since the 1970s. In this study, we used data gathered by the Veterinary Public Health Institutes (IZS) and the Italian Environmental Health Protection Agencies (ARPA) from 2006 to 2019 to investigate toxicity events along the Italian coasts and relate them to the distribution of potentially toxic species. Among the detected toxins (OA and analogs, YTXs, PTXs, STXs, DAs, AZAs), OA and YTX were those most frequently reported. Levels exceeding regulatory limits in the case of OA (≤2,448 μg equivalent kg-1) were associated with high abundances of Dinophysis spp., and in the case of YTXs (≤22 mg equivalent kg-1) with blooms of Gonyaulax spinifera, Lingulodinium polyedra, and Protoceratium reticulatum. Seasonal blooms of Pseudo-nitzschia spp. occur all along the Italian coast, but DA has only occasionally been detected in shellfish at concentrations always below the regulatory limit (≤18 mg kg-1). Alexandrium spp. were recorded in several areas, although STXs (≤13,782 µg equivalent kg-1) rarely and only in few sites exceeded the regulatory limit in shellfish. Azadinium spp. have been sporadically recorded, and AZAs have been sometimes detected but always in low concentrations (≤7 µg equivalent kg-1). Among the emerging toxins, PLTX-like toxins (≤971 μg kg-1 OVTX-a) have often been detected mainly in wild mussels and sea urchins from rocky shores due to the presence of Ostreopsis cf. ovata. Overall, Italian coastal waters harbour a high number of potentially toxic species, with a few HAB hotspots mainly related to DSP toxins. Nevertheless, rare cases of intoxications have occurred so far, reflecting the whole Mediterranean Sea conditions.

A survey of Dinophysis spp. and their potential to cause diarrhetic shellfish poisoning in coastal waters of the United States

Multiple species of the genus Dinophysis produce diarrhetic shellfish toxins (okadaic acid and Dinophysis toxins, OA/DTXs analogs) and/or pectenotoxins (PTXs). Only since 2008 have DSP events (illnesses and/or shellfish harvesting closures) become recognized as a threat to human health in the United States. This study characterized 20 strains representing five species of Dinophysis spp. isolated from three US coastal regions that have experienced DSP events: the Northeast/Mid-Atlantic, the Gulf of Mexico, and the Pacific Northwest. Using a combination of morphometric and DNA-based evidence, seven Northeast/Mid-Atlantic isolates and four Pacific Northwest isolates were classified as D. acuminata, a total of four isolates from two coasts were classified as D. norvegica, two isolates from the Pacific Northwest coast were identified as D. fortii, and three isolates from the Gulf of Mexico were identified as D. ovum and D. caudata. Toxin profiles of D. acuminata and D. norvegica varied by their geographical origin within the United States. Cross-regional comparison of toxin profiles was not possible with the other three species; however, within each region, distinct species-conserved profiles for isolates of D. fortii, D. ovum, and D. caudata were observed. Historical and recent data from various State and Tribal monitoring programs were compiled and compared, including maximum recorded cell abundances of Dinophysis spp., maximum concentrations of OA/DTXs recorded in commercial shellfish species, and durations of harvesting closures, to provide perspective regarding potential for DSP impacts to regional public health and shellfish industry.

Growth, Toxin Content and Production of Dinophysis Norvegica in Cultured Strains Isolated from Funka Bay (Japan)

The successful cultivation of Dinophysis norvegica Claparède & Lachmann, 1859, isolated from Japanese coastal waters, is presented in this study, which also includes an examination of its toxin content and production for the first time. Maintaining the strains at a high abundance (>2000 cells per mL^-1) for more than 20 months was achieved by feeding them with the ciliate Mesodinium rubrum Lohmann, 1908, along with the addition of the cryptophyte Teleaulax amphioxeia (W.Conrad) D.R.A.Hill, 1992. Toxin production was examined using seven established strains. At the end of the one-month incubation period, the total amounts of pectenotoxin-2 (PTX2) and dinophysistoxin-1 (DTX1) ranged between 132.0 and 375.0 ng per mL^-1 (n = 7), and 0.7 and 3.6 ng per mL^-1 (n = 3), respectively. Furthermore, only one strain was found to contain a trace level of okadaic acid (OA). Similarly, the cell quota of pectenotoxin-2 (PTX2) and dinophysistoxin-1 (DTX1) ranged from 60.6 to 152.4 pg per cell^-1 (n = 7) and 0.5 to 1.2 pg per cell^-1 (n = 3), respectively. The results of this study indicate that toxin production in this species is subject to variation depending on the strain. According to the growth experiment, D. norvegica exhibited a long lag phase, as suggested by the slow growth observed during the first 12 days. In the growth experiment, D. norvegica grew very slowly for the first 12 days, suggesting they had a long lag phase. However, after that, they grew exponentially, with a maximum growth rate of 0.56 divisions per day (during Days 24-27), reaching a maximum concentration of 3000 cells per mL^-1 at the end of the incubation (Day 36). In the toxin production study, the concentration of DTX1 and PTX2 increased following their vegetative growth, but the toxin production still increased exponentially on Day 36 (1.3 ng per mL^-1 and 154.7 ng per mL^-1 of DTX1 and PTX2, respectively). The concentration of OA remained below detectable levels (≤0.010 ng per mL^-1) during the 36-day incubation period, with the exception of Day 6. This study presents new information on the toxin production and content of D. norvegica, as well as insights into the maintenance and culturing of this species.

Development of harmful algal blooms species responsible for lipophilic and amnesic shellfish poisoning intoxications in southwestern Mediterranean coastal waters

Mediterranean waters have undergone environmental changes during the last decades leading to various modifications of the structure of phytoplankton populations, especially Harmful Algal Blooms (HABs) species. Monitoring of the potentially toxic phytoplankton species was carried out biweekly in the western Mediterranean coast of Morocco from March 2018 to March 2019. Lipophilic Shellfish Toxins (LSTs) using LC-MS/MS and Domoic Acid (DA) using HPLC-UV were measured in the exploited mollusks, the cockle Acanthocardia tuberculata and the smooth clam Callista chione. We also determined the prevailing environmental factors in four surveyed sites (M'diq bay, Martil, Kaa Asras, and Djawn) selected to cover a variety of coastal ecosystems. Results showed that Pseudo-nitzschia spp. a DA producer species, was abundant with a pick of 50 × 10³ cells l^-1 on October 2018 in Djawn. Dinophysis caudata was the dominate Dinophysis species and showed a maximum density of 2200 cells l^-1 on July in Djawn. Prorocentrum lima, an epibenthic dinoflagellate, appeared rarely in the water column with densities <80 cells l^-1. Gonyaulax spinifera and Protoceratium reticulatum were found occasionally with a maximum density of 160 cells l^-1. Karenia selliformis was detected only five times (<80 cells l^-1) throughout the survey period. LC-MS/MS analyses revealed the presence of OA/DTX3, PTX-2, PTX-2 sa, and PTX-2 sa epi in the cockle at concentrations of up to 44.81 (OA/DTX-3+PTXs) ng g^-1 meat. GYM-A was detected in the clam at concentrations of up to 4.22 ng g^-1 meat. For the first time, AZAs and YTXs were detected in the southwestern Mediterranean with maximum values of 2.49 and 10.93 ng g^-1 meat of cockle, respectively. DA was detected in moderate concentrations not exceeding 5.65 μg g^-1 in both mollusks. Results showed that the observed toxic algae in the water column were responsible from the analysed toxins in the mollusks. It is likely that the southwestern Mediterranean waters could see the development of emergent species producing potent toxins (YTXs, AZAs, GYM-A). These dinoflagellates have to be isolated, ribotyped, and their toxin profiles determined.

Mapping the development of a Dinophysis bloom in a shellfish aquaculture area using a novel molecular qPCR assay

Diarrhetic shellfish toxins produced by certain species of the marine dinoflagellate Dinophysis can accumulate in shellfish in high concentrations, representing a significant food safety issue worldwide. This risk is routinely managed by monitoring programs in shellfish producing areas, however the methods used to detect these harmful marine microbes are not usually automated nor conducted onsite, and are often expensive and require specialized expertise. Here we designed a quantitative real-time polymerase chain reaction (qPCR) assay based on the ITS-5.8S ribosomal region of Dinophysis spp. and evaluated its specificity, efficiency, and sensitivity to detect species belonging to this genus. We designed and tested twenty sets of primers pairs using three species of Dinophysis - D. caudata, D. fortii and D. acuminata. We optimized a qPCR assay using the primer pair that sufficiently amplified each of the target species (Dacu_11F/Dacu_11R), and tested this assay for cross-reactivity with other dinoflagellates and diatoms in the laboratory (11 species) and in silico 8 species (15 strains) of Dinophysis, 3 species of Ornithocercus and 2 species of Phalacroma. The qPCR assay returned efficiencies of 92.4% for D. caudata, 91.3% for D fortii, and 91.5% for D. acuminata, while showing no cross-reactivity with other phytoplankton taxa. Finally, we applied this assay to a D. acuminata bloom which occurred in an oyster producing estuary in south eastern Australia, and compared cell numbers inferred by qPCR to those determined by microscopy counts (max abund. ∼6.3 × 10³ and 5.3 × 10³ cells L^-1 respectively). Novel molecular tools such as qPCR have the potential to be used on-farm, be automated, and provide an early warning for the management of harmful algal blooms.

Prediction of Alexandrium and Dinophysis algal blooms and shellfish contamination in French Mediterranean Lagoons using decision trees and linear regression: a result of 10 years of sanitary monitoring

French Mediterranean lagoons are frequently subject to shellfish contamination by Diarrheic Shellfish Toxins (DSTs) and Paralytic Shellfish Toxins (PSTs). To predict the effect of various environmental factors (temperature, salinity and turbidity) on the abundance of the major toxins producing genera, Dinophysis and Alexandrium, and the link with shellfish contamination, we analysed a 10-year dataset collected from 2010 to 2019 in two major shellfish farming lagoons, Thau and Leucate, using two methods: decision trees and Zero Inflated Negative Binomial (ZINB) linear regression models. Analysis of these decision trees revealed that the highest risk of Dinophysis bloom events occurred at temperature <16.3°C and salinity <27.8, and of Alexandrium at temperature ranging from 10.4 to 21.5°C and salinity >39.2. The highest risk of shellfish contaminations by DSTs and PSTs occurred during the set of conditions associated with high risk of bloom events. Linear regression prediction enables us to understand whether temperature and salinity influence the presence of Alexandrium and affect its abundance. However, Dinophysis linear regression could not be validated due to overdispersion issues. This work demonstrates the tools which could help sanitary management of shellfish rearing areas.

Effect of a short-term salinity stress on the growth, biovolume, toxins, osmolytes and metabolite profiles on three strains of the Dinophysis acuminata-complex (Dinophysis cf. sacculus)

Dinophysis is the main dinoflagellate genus responsible for diarrheic shellfish poisoning (DSP) in human consumers of filter feeding bivalves contaminated with lipophilic diarrheic toxins. Species of this genus have a worldwide distribution driven by environmental conditions (temperature, irradiance, salinity, nutrients etc.), and these factors are sensitive to climate change. The D. acuminata-complex may contain several species, including D. sacculus. The latter has been found in estuaries and semi-enclosed areas, water bodies subjected to quick salinity variations and its natural repartition suggests some tolerance to salinity changes. However, the response of strains of D. acuminata-complex (D. cf. sacculus) subjected to salinity stress and the underlying mechanisms have never been studied in the laboratory. Here, a 24 h hypoosmotic (25) and hyperosmotic (42) stress was performed in vitro in a metabolomic study carried out with three cultivated strains of D. cf. sacculus isolated from the French Atlantic and Mediterranean coasts. Growth rate, biovolume and osmolyte (proline, glycine betaine and dimethylsulfoniopropionate (DMSP)) and toxin contents were measured. Osmolyte contents were higher at the highest salinity, but only a significant increase in glycine betaine was observed between the control (35) and the hyperosmotic treatment. Metabolomics revealed significant and strain-dependent differences in metabolite profiles for different salinities. These results, as well as the absence of effects on growth rate, biovolume, okadaic acid (OA) and pectenotoxin (PTXs) cellular contents, suggest that the D. cf. sacculus strains studied are highly tolerant to salinity variations.

Molecular networking as a novel approach to unravel toxin diversity of four strains of the dominant Dinophysis species from French coastal waters

Some species of the genus Dinophysis contain Diarrhetic shellfish Poisoning (DSP) toxins and are the main threat to shellfish farming in Europe including France. Dinophysis species are known to produce two families of bioactive lipophilic toxins: (i) okadaic acid (OA) and their analogues dinophysistoxins (DTXs) and (ii) pectenotoxins (PTXs). Only six toxins (OA, DTX1, DTX2, DTX3, PTX1 and PTX2) regulated by the European Union Legislation (EC No. 15/2011; 3) are routinely monitored using targeted chemical analysis by liquid chromatography coupled to mass spectrometry (LC-MS/MS) while toxic species of Dinophysis produce many other analogues. To tentatively identify unknown toxin analogues, a recent approach (Molecular Networking, MN) was used based on fragmentation data obtained by untargeted high resolution mass spectrometry (HRMS). An optimization of the data-dependent LC-HRMS/MS acquisition conditions was conducted to obtain more informative networks. The MN was applied to provide an overview of the chemical diversity of four strains belonging to three major Dinophysis species isolated from French coastal waters (D. acuta, D. caudata and the "D. acuminata complex" species D. acuminata and D. sacculus). This approach highlighted species-specific chemical patterns and also that Dinophysis chemical diversity is largely unexplored. Using MN allowed to identify directly known toxins and their relationship between species of Dinophysis, leading to the discovery of five new putative PTX analogues.