Emillie M. F. Passfield

Nodularin is a cyanobacterial toxin predominantly produced by Nodularia spumigena Mertens. This cyanobacterium has been associated with fish, bird, and animal deaths, and the toxin can contaminate fish and shellfish intended for human consumption. With climate change, blooms of Nodularia spumigena are becoming more frequent and more widespread, meaning that the risk this cyanobacterium poses to human health must be evaluated. However, toxicity information is scarce, meaning that data from the closely related toxin class, microcystins, are currently used instead. In the current study, the LD₅₀ of nodularin-R by intraperitoneal injection was found to be 50 µg/kg, consistent with previous reports. For the first time, the LD₅₀ of nodularin-R by oral administration was determined using the voluntary consumption of laced cream cheese (7.5 mg/kg), which is similar to that reported for microcystin-LR (10.9 mg/kg). The use of microcystin toxicology data in food safety assessments for nodularin, therefore, seems reasonable—but it is critical that an oral repeated-dose study is performed on nodularin to better understand the risk posed by this toxin through chronic exposure.

The giant moray eel (GME; Gymnothorax javanicus) is an important marine species that plays a key ecological role in reef systems and is a valued food source for indigenous communities. However, it is well-known that GMEs pose a food safety risk due to their ability to accumulate high levels of ciguatoxins (CTXs), the toxins known to cause ciguatera poisoning. This study assessed the age, CTX levels, elemental composition, and nutritional profile of seven GME specimens collected from Muri Lagoon, Rarotonga (Cook Islands), representing the most detailed compositional investigation on this species. Age was determined for the three largest specimens, with the oldest being 39 years old. All specimens contained ciguatoxins, with Type I (CTX4A derivatives), Type II (CTX3C derivatives), algal-ciguatoxins, and biotransformed metabolites being detected. There was a higher CTX content in the liver samples compared to flesh samples, with the longest–heaviest specimen containing the highest levels. The CTX1B level observed in flesh samples of all seven eel specimens exceeded the recommended safe guidance level proposed by the USFDA. A similar ciguatoxin profile was observed across flesh sections, with the belly flap or top loin containing the highest levels of CTXs in most specimens. No bioactive metabolites produced by co-occurring harmful microalgae, including regulated shellfish toxins, were detected. Elemental analysis determined the presence of 21 elements, including arsenic, low levels of mercury, and the volcanic elements rubidium and strontium. Nutritionally, the GMEs were shown to be a lean protein source; however, due to the ubiquitous bioaccumulation of CTXs, they pose a food safety risk to consumers.

Ciguatera poisoning (CP) is caused by the consumption of marine products contaminated with ciguatoxins (CTXs) produced by dinoflagellates of the genus Gambierdiscus. Analytical methods for CTXs, involving the extraction/purification of trace quantities of CTXs from complex matrices, are numerous in the literature. However, little information on their effectiveness for nonpolar CTXs is available, yet these congeners, contributing to the risk of CP, are required for the establishment of effective food safety monitoring programs. An evaluation of six extraction/purification protocols, performed with CTX3C spiked on fish flesh and a neuroblastoma cell-based assay (CBA-N2a), revealed recoveries from 6 to 45%. This led to the development of an optimized 3-day protocol designed for a large number of samples, with CTX1B and CTX3C eluting in a single fraction and showing recoveries of 73% and 70%, respectively. In addition, a reduction in adverse matrix effects in the CBA-N2a analyses was demonstrated with naturally contaminated specimens, increasing the sensitivity of the method, which now meets the very low guidance level recommended by international agencies. However, efforts are still required to reduce the signal suppression observed in LC-MS/MS analysis. This optimized protocol contributes to the technological advancement of detection methods, promoting food safety and improving CP risk assessment in marine products.

The genus Gambierdiscus produces an array of bioactive hydrophilic and lipophilic secondary metabolites that range in mode of action and toxicity. In this study, the metabolite fingerprint was mapped for thirteen Gambierdiscus, five Coolia and two Fukuyoa species (34 isolates) by assessing the production of 56 characterised secondary metabolites. Gambierdiscus polynesiensis was the only species to produce Pacific-ciguatoxin-3B (P-CTX3B), P-CTX3C, iso-P-CTX3B/C, P-CTX4A, P-CTX4B and iso-P-CTX4A/B. G. australes produced maitotoxin-1 (MTX-1) and MTX-5, G. cheloniae produced MTX-6 and G. honu produced MTX-7. Ubiquitous production of 44-methylgambierone was observed amongst all the Gambierdiscus isolates, with nine species also producing gambierone. Additional gambierone analogues, including anhydrogambierone (tentatively described herein), were also detected in all Gambierdiscus species, two Coolia and two Fukuyoa species. Gambieroxide was detected in G. lewisii and G. pacificus and gambieric acid A was detected in ten Gambierdiscus species, with G. australes (CAWD381) being the only isolate to produce gambieric acids A–D. This study has demonstrated that the isolates tested to date produce the known CTXs or MTXs, but not both, and highlighted several species that produced ‘unknown’ compounds displaying characteristics of cyclic polyethers, which will be the focus of future compound discovery efforts.

This study reports the development of a class of eco-friendlyantifoulingbiocides based on a cyclic dipeptide scaffold, 2,5-diketopiperazine(2,5-DKP). The lead compound cyclo(N-Bip-l-Arg-N-Bip-l-Arg) (1) wassynthesized in gram amounts and used to assess the compatibility withan ablation/hydration coating, efficacy against biofouling, and biodegradation.Leaching of 1 from the coating into seawater was assessedvia a rotating drum method, revealing relatively stable and predictableleaching rates under dynamic shear stress conditions (36.1 +/- 19.7 to 25.2 +/- 9.1 ng(-1) cm(-2) day(-1)) but low or no leaching under static conditions.The coatings were further analyzed using time-of-flight secondaryion mass spectrometry (ToF-SIMS), with 1 seen to localizeat the surface of the coating in a surfactant-like fashion. When coatingswere deployed in the ocean, detectable reductions in biofouling developmentwere measured for up to 11 weeks. After this time, biofouling overwhelmedthe performance of the coating, consistent with leaching kinetics.Biodegradation of 1 in seawater was assessed using theoreticaloxygen demand and analytical quantification. Masking effects wereobserved at higher concentrations of 1 due to antimicrobialproperties, but half-lives were calculated ranging from 13.4 to 16.2days. The results can rationally inform future development towardcommercial antifouling products.