Ostreopsis cf. ovata from the Mediterranean area. Variability in toxin profiles and structural elucidation of unknowns through LC-HRMSn

Ostreopsis spp. once confined to tropical and subtropical areas have recently spread to temperate regions such as the Mediterranean and the Southern-Atlantic coasts of Europe with relevant negative impact on human health through skin contact and inhalation of toxic aerosols. Following Ostreopsis-related outbreaks, we developed a liquid chromatography-high resolution mass spectrometry (LC-HRMS) method for the analysis of algal samples. Our studies characterized O. cf. ovata as producer of palytoxin congeners, including a putative palytoxin and ovatoxins. Toxin profiles of different algal strains appear sometimes different both qualitatively and quantitatively and the presence of further new ovatoxins is emerging. Herein we report on a systematic study of over 40 Mediterranean strains of O. cf. ovata. All of them showed to produce ovatoxins although at different levels. Four types of toxin profiles were identified. Most of the strains produced ovatoxin-a as major component of the toxin profile while a significant number of strains did not produce ovatoxin-b and -c. Unique toxin profiles were found in a strain from the Adriatic coast of Italy, in which ovatoxin-f was the dominant toxin, and in a strain from the French Mediterranean coast, which produced only ovatoxin-b and c. On a per cell basis, toxin contents were in the range 5-230 pg/cell. In light of the structural complexity of ovatoxins, a LC-HRMSn based approach was employed to gain structural insights on known and unknown components of toxin profiles that could be available in too small amounts to be studied by NMR.