Diversity, Toxicity, and Toxin Profiling of Gambierdiscus Strains from Cuba (Caribbean Sea) Reveal C-CTX5 Production in Gambierdiscus silvae

Abstract Ciguatera poisoning (CP) is the most widespread nonbacterial seafood-borne illness worldwide and is endemic in the Caribbean Sea, where it represents a frequent public health concern in Cuba. CP is caused by the consumption of fish contaminated with ciguatoxins (CTXs), which are produced by certain species of the benthic dinoflagellate genus Gambierdiscus and subsequently bioaccumulate through the marine food web. Despite the recognized diversity of Gambierdiscus in the Caribbean Sea, the identification of the species responsible for CTX production remains limited, due to the scarcity of chemical confirmation of these compounds. In this study, we investigated the diversity, toxicity, and toxin profiles of Gambierdiscus species from the coastal waters of Havana (Cuba, Caribbean Sea). Strains were cultured and identified through morphological and molecular analyses, revealing the presence of six species: Gambierdiscus caribaeus, Gambierdiscus carpenteri, Gambierdiscus carolinianus, Gambierdiscus belizeanus, Gambierdiscus australes, and Gambierdiscus silvae. The dominance of G. caribaeus confirms its ecological success in Caribbean reef environments, while the detection of G. australes represents its first report in Cuban and Caribbean waters. Toxicity assessment using the neuroblastoma cell-based assay (N2a CBA) showed limited evidence of CTX-like activity in most strains. In contrast, G. silvae exhibited a clear CTX-like response. Chemical analyses by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) and liquid chromatography coupled to high resolution mass spectrometry (LC-HRMS) revealed the widespread presence of 44-methylgambierone across most species, while gambierone was also detected but at lower concentrations. C-CTX5 was unequivocally detected in G. silvae by both MS techniques. These findings confirm the high diversity of Gambierdiscus in Cuban waters and support the role of G. silvae as a key source of CTXs in the Caribbean, emphasizing the need for combined molecular, functional, and chemical approaches to accurately assess CP risk.