Paralytic Shellfish Poisoning Toxins: Biochemistry and Origin

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.

Genomics Study of the Exposure Effect of Gymnodinium catenatum, a Paralyzing Toxin Producer, on Crassostrea gigas' Defense System and Detoxification Genes

“…The test-dinoflagellate doses (concentrations) were based on field HAB observations of G. catenatum cells [18], [22], [26], [27] and toxic-effect reports of PST producers ( Alexandrium and Gymnodinium genera) [1], [3], [7], [26], [27].…”

“…Saxitoxin (STX) is the representative compound that has a tricyclic guanidine linked to a hydromethyluracil group [2], [3]. PSTs exert their effect by binding reversibly to voltage-sensitive sodium channels on excitable cell membranes and blocking neurotransmission [1], [3]; Alexandrium, Pyrodinium , and Gymnodinium genera are the dominant sources of marine PSTs [7]. Consequently, bivalves' feeding physiology in the presence of toxic dinoflagellates is an important research topic especially on areas where HABs frequently occur.…”

“…Consequently, bivalves' feeding physiology in the presence of toxic dinoflagellates is an important research topic especially on areas where HABs frequently occur. Previous studies show that bivalves have variable feeding responses to toxic algae, which may be related to their HAB exposure history [1], [6], [7], toxin bioaccumulation [1], [3], [6], dinoflagellate toxicity [6], [8], exposure time, and bivalve mollusk species [1], [6], [9].…”

“…C. gigas was exposed to G. catenatum cells under experimental conditions: oysters were fed with the dinoflagellate, analyzed for acute (24 h) and sub-chronic (14 days) periods, and compared to those that received an innocuous microalga ( Isochrysis galbana ) as food; two dinoflagellate doses were tested: 3×10 3 and 30×10 3 cells mL −1 . Exposure to dinoflagellate PST-producers ( Alexandrium and Gymnodinium genera) at a cell density from 10 4 to 10 5 cells L −1 is reported as causative of toxic manifestations in wild mollusks [1], [3], [18].…”

Saxitoxins and okadaic acid group: accumulation and distribution in invertebrate marine vectors from Southern Chile

“…Up to now, 57 analogues have been ascribed to this STX-group, each of them possessing a different toxic capability (>carbamoyltoxins >decarbamoyltoxins > N-sulfocarbamoyltoxins (Ctoxins)) (Perez et al 2011). Among the most important STX-group congers, gonyautoxins (GTX), (GTX4/GTX1, GTX5 and GTX3/GTX2), neosaxitoxin (neoSTX) and saxitoxin (STX) stand out (Kodama 2010;Munday et al 2013). Molluscs, when filtering water, accumulate dinoflagellates and/or STX-group toxins, thereby acquiring high levels of toxins in their digestive glands, which can cause death when they are consumed by people.…”