New stage of the study on domoic acid-producing diatoms : A finding of Nitzschia navis-varingica that produces domoic acid derivatives as major toxin components

We reported Nitzschia navis-varingica as a new domoic acid (DA)-producing diatom, and furthermore reported its wide distribution in Asian waters. However the surveys were performed only in limited area of each country. In order to obtain more detailed information, screening of N. navis-varingica was primarily performed in the Philippines. During the survey, we confirmed that all strains of N. navis-varingica isolated from Bulacan, Manila Bay did not produce DA, but did produce isodomoic acids A (IA) and B (IB). The confirmation of IA and IB was done by the analyses of UV-spectra, LC-MS/MS, proton NMR and ^<13>C NMR. Re-observation of the toxin composition including IA and IB simultaneously with DA was performed on the former chromatograms. All the strains positive for DA and/or its derivatives isolated from estuary areas of Bacoor, Tanauan and San Roque, were confirmed to produced DA and IB, indicating that there is a local difference in toxin composition in the Philippines. All of the toxic strains were identified as N. navis-varingica. This is the first report of pennate diatom that produces IA and IB instead of DA as major toxin component. This finding might be a useful step in pursuing the DA production mechanism. Additionally fourty one Pseudo-nitzschia strains isolated from offshore areas of above mentioned estuaries were tested for DA, but all of them did not show any sign of DA production.