Gambierdiscus polynesiensis from New Caledonia (South West Pacific Ocean): Morpho-molecular characterization, toxin profile and response to light intensity.

Gambierdiscus is known to produce neurotoxins associated with ciguatera poisoning (CP). In New Caledonia (NC), South West Pacific Ocean, there is currently a significant knowledge gap regarding CP and the microalgae linked to this foodborne illness. This study describes a new strain of Gambierdiscus polynesiensis, 19PV93, isolated from the west coast of NC. The strain was isolated and cultured for morpho-molecular characterization to determine its phylogenetic position. Toxic activity was assessed using a cell-based assay with neuroblastoma cells (CBA-N2a), and the toxin profile was characterized using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) to evaluate potential risks to human health. Regarding the toxin profile, G. polynesiensis was characterized by the presence of gambierone, 44-methylgambierone (44-MeG), and an atypical ciguatoxin profile consisting solely of ciguatoxin-4A (CTX4A) and -4B (CTX4B). This finding confirms intraspecific variations in toxin profiles between strains from different geographic origins. In culture, G. polynesiensis demonstrated a preference for relatively low irradiances (50 to 100 µmol photons m⁻² s⁻¹) compared to the higher light intensities often encountered in their natural environment. The impact of light on toxin concentrations was found to be inversely related to light intensity, with higher quotas observed at lower light levels. Gambierdiscus employed non-photochemical quenching as a photoprotective strategy to safeguard PSII from excessive light, particularly during both short-term and long-term exposure. However, this dissipation strategy alone appears insufficient, as photoinhibition was consistently observed, and the electron transfer rate and yield along the electron transfer chain rapidly declined with increasing light intensity.