Abstract
Severe toxicity was detected in mussels from Bizerte Lagoon (Northern Tunisia) using routine mouse bioassays for detecting diarrheic and paralytic toxins not associated to classical phytoplankton blooming. The atypical toxicity was characterized by rapid mouse death. The aim of the present work was to understand the basis of such toxicity. Bioassay-guided chromatographic separation and mass spectrometry were used to detect and characterize the fraction responsible for mussels’ toxicity. Only a C17-sphinganine analog mycotoxin (C17-SAMT), with a molecular mass of 287.289 Da, was found in contaminated shellfish. The doses of C17-SAMT that were lethal to 50% of mice were 750 and 150 μg/kg following intraperitoneal and intracerebroventricular injections, respectively, and 900 μg/kg following oral administration. The macroscopic general aspect of cultures and the morphological characteristics of the strains isolated from mussels revealed that the toxicity episodes were associated to the presence of marine microfungi (Fusarium sp., Aspergillus sp. and Trichoderma sp.) in contaminated samples. The major in vivo effect of C17-SAMT on the mouse neuromuscular system was a dose- and time-dependent decrease of compound muscle action potential amplitude and an increased excitability threshold. In vitro, C17-SAMT caused a dose- and time-dependent block of directly- and indirectly-elicited isometric contraction of isolated mouse hemidiaphragms.
Highlights
Shellfish are exposed to odorous and bioactive secondary metabolites through the ingestion of harmful microalgae, cyanobacteria, consumption of contaminated food and absorption of dissolved compounds from the water column, facilitating transfer through the web food chain [1].Usually, phycotoxins are classified into five categories according to their chemical structures, including derivatives of amino acids, derivatives of purines, cyclic imines, non-nitrogenous linear polyethers and cyclic polyethers [2]
The results revealed the presence of three different strains of marine microfungus, and the genera Aspergillus (Figure 7), Fusarium and Trichoderma were identified
Which are known to produce mycotoxins [12,13], the non-identification of any conventional phycotoxins in contaminated samples, and the evidence from the retention time together with the mass accuracy close to 1 ppm of the toxic compound and C17-SPA shows that the compound responsible for the toxicity of mussels collected from shellfish farming areas in Bizerte Lagoon is unequivocally a mycotoxin structurally similar to C17-SPA
Summary
Phycotoxins are classified into five categories according to their chemical structures, including derivatives of amino acids (domoic acid), derivatives of purines (saxitoxin and derivatives), cyclic imines (gymnodimines, spirolides, pinnatoxins), non-nitrogenous linear polyethers (okadaic acid, pectenotoxins, azaspiracids) and cyclic polyethers (yessotoxins, brevetoxins, ciguatoxins) [2]. An increasing number of toxic events occurred due to emerging toxins as detected by the mouse bioassay without any identification of known toxinogenic organism or toxins [3]. Large number of phytopathogenic and food spoilage fungi (for example, Aspergillus, Penicillium, Fusarium and Alternaria species) produce some toxic compounds called mycotoxins [5]. These secondary metabolism products form a polymorphic family with various structures and toxicological properties, including trichothecenes, aflatoxins, sterigmatocystin, fumonisins and Alternaria alternata f. These secondary metabolism products form a polymorphic family with various structures and toxicological properties, including trichothecenes, aflatoxins, sterigmatocystin, fumonisins and Alternaria alternata f. sp. lycopersici (AAL)-toxins [6,7]
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