Screening of diatoms producing domoic acid and its derivatives in the Philippines

Domoic acid is the known causative agent responsible for amnesic shellfish poisoning (ASP). Although there is only one documented ASP case in the world, there is a potential of its occurrence in Southeast Asian countries. However, limited information on domoic acid producing diatoms is available except for Nitzschia navis-varingica, which is known to produce significant levels of domoic acid. In order to obtain fundamental data on domoic acid producing diatoms, screening of Pseudo-nitzschia and Nitzschia species were primarily performed in the Philippines. Two source areas, i.e. Manila Bay and Iba estuary of Luzon Island, were selected for observation of these diatoms. Fifty eight isolates of Pseudo-nitzscia and 18 isolates of Nitzschia-like diatoms were prepared from Manila Bay and Iba estuary, respectively. These isolates were cultured and tested for the production of domoic acid and its derivatives. Pseudo-nitzscia strains did not show any signs of domoic acid production. Five out of 18 Nitzschia isolates were confirmed to produce isodomoic acids A and B. Comparison of sonication and boiling in water bath as extraction methods was investigated and results showed that both methods yielded comparable amounts of domoic acid. Stability of domoic acid extracted by boiling was also investigated and was found out to be stable at room temperature for ten days. Results implied an advantageous and convenient way of sample preparation and preservation for international transport

Two new ASP toxin production types in strains of Nitzschia navis-varingica from the Philippines

Nitzschia navis-varingica, a diatom widely distributed in brackish waters of Japan and Southeast Asia, was found to produce domoic acid (DA) and its derivatives isodomoic acids A (IA) and B (IB) as the major toxin components. The toxin composition of N. navis-varingica has previously been classified into three types namely DA type (produces DA and IB with an IB ratio of less than 10%), DA-IB type (the IB ratio is 20-80%) and IA-IB type (produces no DA). In the latter type, the ratio of IB tends to be higher in southern areas. In order to investigate more detailed distribution of ASP toxin types of N. navis-varingica, a screening was performed in three localities on Luzon Island, the Philippines. All isolates from one locality, Bulacan, were the DA-IB type. Isolates from the other two localities, Alaminos and Cavite, were found to make up two different and never described toxin composition types, the IB and the DA-IA-IB types, respectively. Sub-strains established from a representative parent of each new toxin composition type showed the same toxin composition as the parental strains. These results suggest that ASP toxin composition types of N. navis-varingica are more complex than previously reported.Proceedings of the Horiba International Conference "New Direction of Ocean Research in the Western Pacific" : Past, Present and Future of UNESCO/IOC/WESTPAC Activity for 50 years and the JSPS Project "Coastal Marine Science"Section I: Research Articles/Harmful microalga

Two new ASP toxin production types in strains of Nitzschia navis-varingica from the Philippines

Nitzschia navis-varingica, a diatom widely distributed in brackish waters of Japan and Southeast Asia, was found to produce domoic acid (DA) and its derivatives isodomoic acids A (IA) and B (IB) as the major toxin components. The toxin composition of N. navis-varingica has previously been classified into three types namely DA type (produces DA and IB with an IB ratio of less than 10%), DA-IB type (the IB ratio is 20-80%) and IA-IB type (produces no DA). In the latter type, the ratio of IB tends to be higher in southern areas. In order to investigate more detailed distribution of ASP toxin types of N. navis-varingica, a screening was performed in three localities on Luzon Island, the Philippines. All isolates from one locality, Bulacan, were the DA-IB type. Isolates from the other two localities, Alaminos and Cavite, were found to make up two different and never described toxin composition types, the IB and the DA-IA-IB types, respectively. Sub-strains established from a representative parent of each new toxin composition type showed the same toxin composition as the parental strains. These results suggest that ASP toxin composition types of N. navis-varingica are more complex than previously reported.Proceedings of the Horiba International Conference "New Direction of Ocean Research in the Western Pacific" : Past, Present and Future of UNESCO/IOC/WESTPAC Activity for 50 years and the JSPS Project "Coastal Marine Science"Section I: Research Articles/Harmful microalga

ISOLATION OF ASP TOXIN-PRODUCING NITZSCHIA FROM THAILAND

Nitzschia navis-varingica is recognized as the major ASP toxin producer other than Pseudo-nitzschia species. Surveys on the distribution and the toxin production of this diatom has been conducted in a few countries in eastern Asia and expanded to Thailand. Eighteen isolates from Thailand showed the positive result for the ASP toxin production is DA and IB, although the ratio of IB was much lower than those of the isolates from southern countries including Okinawa, Japan, the Philippines and Vietnam

Screening of diatoms producing domoic acid and its derivatives in the Philippines

Domoic acid is the known causative agent responsible for amnesic shellfish poisoning (ASP). Although there is only one documented ASP case in the world, there is a potential of its occurrence in Southeast Asian countries. However, limited information on domoic acid producing diatoms is available except for Nitzschia navis-varingica, which is known to produce significant levels of domoic acid. In order to obtain fundamental data on domoic acid producing diatoms, screening of Pseudo-nitzschia and Nitzschia species were primarily performed in the Philippines. Two source areas, i.e. Manila Bay and Iba estuary of Luzon Island, were selected for observation of these diatoms. Fifty eight isolates of Pseudo-nitzscia and 18 isolates of Nitzschia-like diatoms were prepared from Manila Bay and Iba estuary, respectively. These isolates were cultured and tested for the production of domoic acid and its derivatives. Pseudo-nitzscia strains did not show any signs of domoic acid production. Five out of 18 Nitzschia isolates were confirmed to produce isodomoic acids A and B. Comparison of sonication and boiling in water bath as extraction methods was investigated and results showed that both methods yielded comparable amounts of domoic acid. Stability of domoic acid extracted by boiling was also investigated and was found out to be stable at room temperature for ten days. Results implied an advantageous and convenient way of sample preparation and preservation for international transport