Screening of diatoms that produce ASP toxins in Southernmost Asian waters

In order to explore the detailed distribution of N. navis-varingica that produces ASP toxins in Asian waters, a screening was made in four areas of Indonesia and a part of Malaysia. Diatom samples were collected by a plankton net. Nitzschia-like di- atoms were isolated from crude pre-cultures and cultured in f/2 medium followed by HPLC-fluorescence analysis. Unlike other Asian countries, Nitzschia navis-varingica-like diatoms were rare in Indonesian and Malaysian samples, which is partly attributa- ble to the extreme pH and salinity at some of the localities. Fifteen, six and eleven isolates were obtained from South Sulawesi, Lampung and Sangihe Island in Indonesia, respectively, none from Jakarta Bay, Indonesia and eight strains from Kota Kinabalu, Malaysia. All of the fifteen strains from South Sulawesi (Panyula) produced toxins. They produced on average 2.7 pg toxin cell �1 with the toxin profile of DA : IB (98 : 2) similar to results on strains from Thailand and northern Japan. This toxin production was confirmed by LC-MS/MS analysis. These toxin-producing strains were identified as N. navis-varingica. Eleven sub-strains of a single parental strain showed the same toxin profile (on average 1.1 pg toxin cell �1 , DA : IB�94 : 6). The remaining Nitzschia strains did not produce ASP toxins. Twenty isolates of Pseudo-nitzschia from Lampung Bay were not found to produce ASP toxins.