|Vol. 3 (No. 1), pp. 1-38, 2010||doi:10.5047/absm.2010.00301.0001|
Laboratory of Marine Biochemistry, Department of Aquatic Biosciences, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo 113-8657, Japan
(Received on September 8, 2009; Accepted on October 13, 2009; Published online on April 9, 2010)
Abstract: Plankton feeders such as bivalves often become toxic. Human consumption of the toxic bivalve causes severe food poisoning, including paralytic shellfish poisoning (PSP) which is the most dangerous because of the acuteness of the symptoms, high fatality and wide distribution throughout the world. Accumulation of PSP toxins in shellfish has posed serious problems to public health and fisheries industry. The causative organisms of PSP toxins are known to be species of dinoflagellates including those belonging to the genus Alexandrium, Gymnodinium catenatum and Pyrodinium bahamense var. compressum. Bivalves accumulate PSP toxins during a bloom of these dinoflagellates. Thus, the dinoflagellate toxins have been considered as being concentrated in bivalves through food web transfer. However, field studies on the toxin level of bivalves in association with the abundance of toxic dinoflagellates could not support the idea. A kinetics study on toxins by feeding experiments of cultured dinoflagellate cells to bivalves also showed similar results, indicating that toxin accumulation of bivalves is not caused by simple accumulation of toxins due to food-web transfer. Based on the discovery of toxin-producing bacterium in the cells of toxic dinoflagellates, this study suggests that PSP toxins in toxic dinoflagellates are catabolites of bacterial substance in dinoflagellate cells. On the other hand, tetrodotoxin (TTX), a puffer toxin, is reported to be produced by some species of bacteria. Thus, the origin of TTX of puffer is considered to be bacteria. However, the mechanism for puffer to possess TTX through bacteria is unknown. The present study revealed that organisms bearing either TTX or PSP toxins possess both toxins, although the proportion of both is different among the specimens. In fact, a significant level of TTX is detected in A. tamarense. In addition, TTX-like toxin-producing bacteria are found to be infected in the liver of toxic specimens of puffer. These findings strongly suggest that a similar mechanism between bacteria and toxic organisms is involved in the production of TTX and/or PSP toxins in toxic organisms.
Keywords: paralytic shellfish poisoning toxins, saxitoxin, gonyautoxin, tetrodotoxin, dinoflagellate, Alexandrium tamarense, bivalve, intracellular bacteria, bacterial infection
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