Evidence of the bioaccumulation of ciguatoxins in giant clams (Tridacna maxima) exposed to Gambierdiscus spp. cells

Abstract

Ciguatera Fish Poisoning (CFP) is a foodborne disease classically related to the consumption of tropical coral reef fishes contaminated with ciguatoxins (CTXs), neurotoxins produced by dinoflagellates of the Gambierdiscus genus. Severe atypical ciguatera-like incidents involving giant clams, a marine resource highly consumed in the South Pacific, are also frequently reported in many Pacific Islands Countries and Territories. The present study was designed to assess the ability of giant clams to accumulate CTXs in their tissues and highlight the potential health risks associated with their consumption. Since giant clams are likely to be exposed to both free-swimming Gambierdiscus cells and dissolved CTXs in natural environment, ex situ contamination experiments were conducted as follows: giant clams were exposed to live or lyzed cells of TB92, a highly toxic strain of G. polynesiensis containing 5.83±0.85pg P-CTX-3C equiv.cellvs. HIT0, a weakly toxic strain of G. toxicus containing only (2.05±1.16)×10pg P-CTX-3C equiv.cell, administered over a 48h period at a concentration of 150cellsmL. The presence of CTXs in giant clams tissues was further assessed using the mouse neuroblastoma cell-based assay (CBA-N2a). Results showed that giant clams exposed to either lyzed or live cells of TB92 were able to bioaccumulate CTXs at concentrations well above the safety limit recommended for human consumption, i.e. 3.28±1.37 and 2.92±1.03ng P-CTX-3C equiv.g flesh (wet weight), respectively, which represented approximately 3% of the total toxin load administered to the animals. In contrast, giant clams exposed to live or lyzed cells of HIT0 were found to be free of toxins, suggesting that in the nature, the risk of contamination of these bivalves is established only in the presence of highly toxic blooms of Gambierdiscus. Liquid chromatography-mass spectrometry (LC-MS/MS) analyses confirmed CBA-N2a results and also revealed that P-CTX-3B was the major CTX congener retained in the tissues of giant clams fed with TB92 cells. To the best of our knowledge, this study is the first to provide evidence of the bioaccumulation of Gambierdiscus CTXs in giant clams and confirms that these bivalve molluscs can actually constitute another pathway in ciguatera poisonings. While most monitoring programs currently focus on fish toxicity, these findings stress the importance of a concomitant surveillance of these marine invertebrates in applicable locations for an accurate assessment of ciguatera risk.

Intraspecific Variability in the Toxin Production and Toxin Profiles of In Vitro Cultures of Gambierdiscus polynesiensis (Dinophyceae) from French Polynesia

“…Several Gambierdiscus and Fukuyoa species/strains have been identified as likely producers of CTXs or CTX-like compounds, as measured by Mouse Biological Assay (MBA) [15,21,40,41], Receptor Binding Assay (RBA) [24], neuroblastoma cell-based assay (CBA-N2a) [42][43][44][45], fluorescent calcium flux assay [46], or liquid chromatography-tandem mass spectrometry (LC-MS/MS) [47][48][49][50][51]. However, the formal confirmation of the presence of previously characterized CTX-and/or MTX-group compounds using LC-MS/MS has been demonstrated only in a limited number of species, i.e., F. paulensis, G. australes, G. caribaeus, G. excentricus, G. pacificus, G. polynesiensis, and G. toxicus, although for this latter species, a potential misidentification of the species is likely [38].…”

“…Only two species proved significantly more toxic than the others, producing pg amounts of CTXs, namely G. polynesiensis [24,49,51] and G. excentricus [44,54,55], and are recognized as important toxin-producing species in the South Pacific and the Atlantic Oceans, respectively. As an example, published toxicity records for G. polynesiensis range from 1.2 up to 18.2 pg cell −1 , as determined by either RBA [24], CBA-N2a [47,56], or LC-MS/MS [49].…”

“…Thus, CP risk assessment programs currently conducted in this region primarily focus on the monitoring of the abundance of this key toxin-producing species using species-specific molecular assays [54,56]. At least 11 distinct P-CTX congeners have been previously characterized in this species, namely P-CTX4B, P-CTX4A (52-epi-P-CTX4B), P-CTX3C, P-CTX3B (49-epi-P-CTX3C), M-seco-P-CTX3C methyl acetal, 2-hydroxy-P-CTX3C, 54-deoxy-P-CTX1B, 52-epi-54-deoxy-P-CTX1B, 51-hydroxy-P-CTX3C, M-seco-P-CTX3C, and M-seco-P-CTX4A/4B [24,47,70,71].…”

Transcriptomic analysis of polyketide synthases in a highly ciguatoxic dinoflagellate, Gambierdiscus polynesiensis and low toxicity Gambierdiscus pacificus, from French Polynesia

“…The current study conducted a comparative analysis of the transcriptomes of two Gambierdiscus species from French Polynesia, a highly ciguatoxic G. polynesiensis isolated from the Australes Archipelago (strain TB92), and a co-occurring low-or non-toxic species, G. pacificus (MUR4), with the goal of identifying the diversity of PKS transcripts expressed in common or unique to their very different toxin profiles. G. polynesiensis TB92 produces Pacific ciguatoxins of Type 1 (P-CTX4A, P-CTX4B) and Type 2 (P-CTX3C, 49-epi-P-CTX3C, M-seco-P-CTX3C, M-seco-P-CTX 4A) ladder structures [33,34]. This species also produces 44-methyl gambierone (44MG, formerly known as MTX3) [35], a ubiquitous polyether compound found in the genera Gambierdiscus and Fukuyoa [13,36,37].…”

Toxicity screening of 13 Gambierdiscus strains using neuro-2a and erythrocyte lysis bioassays

“…Algal turfs appear to be very suitable substrates as support for Gambierdiscus, even when compared to macrophytes (Leaw et al, 2016). It is commonly assumed that the primary flux occurs from herbivorous grazers of such macro-algae to carnivorous fish (Ledreux et al, 2014), though other vectors such as crustaceans, echinoderms, and bivalves have been implicated (Kelly et al, 1992;Laurent et al, 2008;Roué et al, 2016;Silva et al, 2015). During this accumulation process CTXs are biotransformed, frequently resulting in metabolites of greater toxicities than the algal parent compounds (Lehane and Lewis, 2000).…”