Morphological and molecular characterization of Pseudo-nitzschia species from the Levantine Basin (Northeastern Mediterranean) and assessment of domoic acid production

Domoic acid (DA) is a water-soluble neurotoxin mainly produced by the diatom genus Pseudo-nitzschia. While several potentially toxic species of Pseudo-nitzschia have been reported in Turkish coastal waters, toxicity studies have remained localized to the Sea of Marmara. In this study, three Pseudo-nitzschia species; P. arenysensis (non-toxic), P. brasiliana, and P. galaxiae (both potentially toxic), were isolated from the Levantine Basin of the northeastern Mediterranean Sea. Species identification was confirmed using scanning electron microscopy and molecular phylogeny based on 18S ribosomal RNA (rRNA) and rbcL plastid DNA. The rbcL topology in particular revealed high sequence identity between the newly sequenced Mediterranean strains and existing global database references. Specific growth rates (μ) reached 0.87 d−1 for P. arenysensis, 0.90 d−1 for P. brasiliana, and 0.98 d−1 for P. galaxiae, with all cultures transitioning to the stationary phase between days 7 and 9. Following cultivation, DA production was screened using ELISA and HPLC-DAD during the stationary phase of the growth. No detectable levels of DA were found in any of the isolated strains. These results provide the first integrated morphological, molecular, and toxicological data for these species in the region, contributing to harmful algal bloom (HAB) monitoring efforts in the northeastern Mediterranean.