Assessment of the growth and toxicity of different strains of Gambierdiscus sp.

Abstract: Microalgae of the genus Gambierdiscus are producers of precursors of ciguatoxins (CTXs), which bioaccumulate in the marine trophic chain and are responsible for ciguatera fish poisoning in humans. Ciguatera is a foodborne illness typically known as a tropical disease, but ciguatera cases are being increasingly reported in the North-Eastern Atlantic. The appearance of fish contaminated with CTXs has become more and more common in areas such as the Canary Islands, but the mechanisms underlying the bioaccumulation and biotransformation of the CTXs in this region are still poorly discerned (Soliño & Costa, 2020).

The study presented here is part of the European project “Ciguarisk” and has the objective to assess cell growth and toxin production of two Gambierdiscus strains from the Atlantic region selected for fish feeding experiments, i.e., G. excentricus IRTA-SMM-17-429 and G. carolineanus BEA1923. Cell growth was performed in culture flasks under the same culture conditions, using a semi-continuous batch approach. The culture method is aimed to harvest the highest biomass production possible for use in dietary exposure experiments in fish. Two culture media (L1 and F2) were evaluated for their influence on the growth of the strains. Both media were suitable for culturing Gambierdiscus, although some slight differences were observed in growth rates and cell behaviour. G. excentricus IRTA-SMM-17-429 presented slower growth with respect to G. carolineanus BEA1923 in all conditions tested. Ciguatoxins were extracted from fresh biomass samples and pre-purified using liquid-liquid partitioning. CTX-like toxicity of the strains was screened using the neuroblastoma neuro-2a assay (Caillaud et al., 2010). Preliminary data suggest that G. excentricus IRTA-SMM-17-429 is more toxic than G. carolineanus BEA1923.

These results presented in this study are in accordance with previous studies on other strains of G. carolinianus and G. excentricus (Pisapia et al., 2017). Further studies will focus on culture optimization and scale-up, quantitation of the toxic content, and micro-encapsulation of the biomass for the feeding experiments. The results obtained from this project will ultimately help to a better understanding of the bioaccumulation and biotransformation of CTXs in the food chain in the Atlantic region.