Ciguatéra : Effets du pH et de la disponibilité en azote sur la croissance et la production de toxines chez Gambierdiscus polynesiensis [May 6, 2021]



Ciguatera poisoning (CP) is the most prevalent phycotoxin-related seafood poisoning across the globe. It results from the consumption of fish and marine invertebrates contaminated with ciguatoxins (CTX), which are toxic metabolites produced by the microalgae Gambierdiscus. Originally limited to tropical and sub-tropical areas, CP is now extending to more temperate regions worldwide, a likely consequence of the drastic modifications experienced by island ecosystems as a result of global change. Gambierdiscus polynesiensis, a species reported only from to the Pacific Ocean so far, is the most potent Gambierdiscus species described to date. It is therefore regarded as a biomarker of ciguateric risk in monitoring programs currently conducted in French Polynesia.
In the context of global change, this thesis aimed at assessing the potential influence of environmental drivers (i.e., ocean acidification and eutrophication) on the health risk associated with G. polynesiensis proliferation in French Polynesian lagoons.

First, the performance of three CTX detection methods, namely the mouse neuroblastoma cell-based assay (CBA-N2a), the fluorescent receptor-binding assay (RBA-F) and the liquid chromatography-tandem mass spectrometry (LC-MS/MS) was compared. Our results outlined  the relevance of an approach that combines the use of both CBA-N2a and LC-MS/MS, as this latter method is able to complete the high sensitivity of CBA-N2a and to identify each characterized CTX congener present in Gambierdiscus extracts.
Second, the toxicological analyses conducted on four G. polynesiensis clones isolated from different archipelagoes in French Polynesia, confirmed the existence of intraspecific variation and allow updating current toxin profile data. The identification of four additional CTX analogs and the detection of gambierone and 44-methyl-gambierone constitute a novel finding.
Finally, the effects of pH and nitrogen source/availability in the culture medium on G. polynesiensis’ growth and toxin production were examined. Under low pH conditions and/or supply of urea as the nitrogen source, a lower growth rate was observed. Conversely, an increase of the overall toxicity and a diversification of the toxin profile were evidenced.

More widely, this work opens interesting research avenues with regards to the understanding of CP risk in French Polynesia and to the targeted production of high value-added CTX standards. Such materials are essential for the implementation of common strategies in CP risk management programs, particularly in countries most vulnerable to the health and socio-economic impacts of CP.



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