Screening of cyclic imine and paralytic shellfish toxins in isolates of the genus Alexandrium (Dinophyceae) from Atlantic Canada.

The dinoflagellate genus Alexandrium Halim has frequently been associated with harmful algal blooms. Although a number of species from this genus are known to produce paralytic shellfish toxins (PST) and/or cyclic imines (CI), studies on comprehensive toxin profiling using techniques capable of detecting the full range of PST and CI analogues are limited. Isolates of Alexandrium spp. from Atlantic Canada were analyzed by targeted and untargeted liquid chromatography-tandem mass spectrometry (LC-MS). Results showed a number of distinct profiles and wide ranging cell quotas of PST and spirolides (SPX) in both A. catenella (Whedon & Kofoid) Balech and A. ostenfedii (Paulsen) Balech & Tangen. The concentration of PST in A. catenella ranged from 0.0029 to 54 fmol cell with the major components being C2 and GTX4. In addition, putative PST metabolites were confirmed for the first time in A. catenella by high resolution MS/MS. By comparison, A. ostenfeldii isolates showed much lower concentrations of PST (<LOD to 2 fmol cell) and high total levels of SPX (14 to 43 fmol cell). The SPX profile of the A. ostenfeldii strains mainly included 13-desmethyl SPX-C, SPX-C and 20-methyl SPX-G, with low levels of other SPX and gymnodimine-like analogues detected by untargeted -high-resolution LC-MS. This work demonstrates the importance of using screening methods capable of detecting the full suite of PST and CI compounds when analyzing Alexandrium isolates for toxin production and adds further complexity to the known toxin profiles of this genus.