Gonyaulax monilata: population growth and development of toxicity in cultures

Unknown Extracellular and Bioactive Metabolites of the Genus Alexandrium: A Review of Overlooked Toxins

Various species of Alexandrium can produce a number of bioactive compounds, e.g., paralytic shellfish toxins (PSTs), spirolides, gymnodimines, goniodomins, and also uncharacterised bioactive extracellular compounds (BECs). The latter metabolites are released into the environment and affect a large range of organisms (from protists to fishes and mammalian cell lines). These compounds mediate allelochemical interactions, have anti-grazing and anti-parasitic activities, and have a potentially strong structuring role for the dynamic of Alexandrium blooms. In many studies evaluating the effects of Alexandrium on marine organisms, only the classical toxins were reported and the involvement of BECs was not considered. A lack of information on the presence/absence of BECs in experimental strains is likely the cause of contrasting results in the literature that render impossible a distinction between PSTs and BECs effects. We review the knowledge on Alexandrium BEC, (i.e., producing species, target cells, physiological effects, detection methods and molecular candidates). Overall, we highlight the need to identify the nature of Alexandrium BECs and urge further research on the chemical interactions according to their ecological importance in the planktonic chemical warfare and due to their potential collateral damage to a wide range of organisms.

Grazer cues induce stealth behavior in marine dinoflagellates

Chain formation is common among phytoplankton organisms but the underlying reasons and consequences are poorly understood. Here we show that chain formation is strongly impaired by waterborne cues from copepod grazers in the dinoflagellate Alexandrium tamarense. Chains of Alexandrium cells exposed to copepod cues responded by splitting into single cells or shorter chains. Motion analysis revealed significantly lower swimming velocities for single cells compared with chains, with two- to fivefold higher simulated predator encounter rates for two- and four-cell chains, respectively. In addition, the few remaining two-cell chains in grazed treatments were swimming at approximately half the speed of two-cell chains in treatments without grazers, which reduced encounter rates with grazers to values similar to that of single cells. Chain length plasticity and swimming behavior constitute unique mechanisms to reduce encounters with grazers. We argue that dinoflagellates can regulate the balance between motility and predator avoidance by adjusting chain length. The high predator encounter rate for motile chains may have contributed to the low prevalence of chain formation in motile phytoplankton compared with in nonmotile phytoplankton where chain formation is more common.

Kinetic properties of saxitoxin in Atlantic salmon (Salmo salar) and Atlantic cod (Gadus morhua)

The disposition of STX in Atlantic salmon (Salmo salar) and Atlantic cod (Gadus morhua) was studied after intraperitoneal (IP) injection (5 microg STX/kg bm and 3.43 microg (3)H-STXeq/kg bw respectively), intravenous (IV) injection (5 microg STX/kg bm, only salmon) and waterborne exposure (50 microg STXeq/L, only salmon). Plasma concentrations in salmon were quantified using a receptor binding assay and cod tissues were analyzed using scintillation counting of tissue extracts and autoradiography of whole fish slices. The estimated elimination half-life (T(1/2)) after IV administration of STX in salmon was 102.6 min. The volume of distribution (Vz) was observed to be 467.2 mL/kg and the total body clearance (Cl(T)) was 3.2 mL/min/kg. Waterborne exposure clearly showed that salmon absorbed PSP toxins directly from the water. In cod, (3)H-STX was observed in gills, muscle, brain, liver and posterior kidney from 30 to 480 min. The lowest concentrations of (3)H-STX were found in brain and muscle, whereas posterior kidney contained the majority of the toxin. Autoradiograms confirmed the high levels of (3)H-STX in the kidneys, indicating that renal excretion was the main elimination route. Buildup of harmful levels in edible tissue is not very likely due to the low concentrations accumulated in muscle tissue and rapid excretion.

Associated bacterial flora, growth, and toxicity of cultured benthic dinoflagellates Ostreopsis lenticularis and Gambierdiscus toxicus

The growth, toxicity, and associated bacterial flora of 10 clonal cultures of the toxic benthic dinoflagellates Ostreopsis lenticularis and Gambierdiscus toxicus isolated from the coastal waters of southwest Puerto Rico have been examined. Clonal cultures of O. lenticularis grew more rapidly and at broader temperature ranges than those of G. toxicus. All five Ostreopsis clones were toxic, while only one of the five Gambierdiscus clones was poisonous. The degree of toxicity among poisonous clones was highly variable. The number of associated bacterial genera and their frequency of occurrence were quite variable among clones of both dinoflagellate genera. Bacterial isolates represented six genera (Nocardia, Pseudomonas, Vibrio, Aeromonas, Flavobacterium, and Moraxella) in addition to coryneform bacteria. Extracts of dinoflagellate-associated bacteria grown in pure culture were not toxic. Gambierdiscus clones were characterized by the frequent presence of Pseudomonas spp. (four of five clones) and the absence of coryneforms. In O. lenticularis, only one of five clones showed the presence of Pseudomonas spp., and Moraxella sp. was absent altogether. Detailed analyses of toxicity and associated microflora in a selected Ostreopsis clone, repeatedly cultivated (four times) over a period of 160 days, showed that peak cell toxicities developed in the late static and early negative culture growth phases. Peak Ostreopsis cell toxicities in the stationary phase of culture growth were correlated with significant increases in the percent total bacteria directly associated with these cells. Changes in the quantity of bacteria directly associated with microalgal cell surfaces and extracellular matrices during culture growth may be related to variability and degree of toxicity in these laboratory-cultured benthic dinoflagellates.

Acute toxic effects in mice of an extract from the marine algae Gonyaulax monilata

Unialgal cultures of Gonyaulax monilata were cultured and harvested. A modified Westphall procedure was used to prepare an extract which did not contain saxitoxin, the gonyautoxins and structurally related toxins. The extract was administered i.p. to young adult, male CD-1 mice and produced: sedation, abdominal constriction, fecal clumping in the perianal area, ataxia, tremors, cyanosis, loss of reflexes, convulsions and death (LD50 = 2.28 mg/kg). Gross and microscopic pathology in the treated mice included: acute active hyperemia of the viscera, multifocal areas of necrosis of the musculature of the intestinal wall and diaphragm and the presence of cytoplasmic vacuoles in the peripheral margins of the acinar portion of the pancreas. Clinical pathology of the mice which survived 24 hr included significant elevation in the levels of serum lactic dehydrogenase, glutamic pyruvic and glutamic oxaloacetic transaminases. Some of these mice also had significantly decreased white blood cell counts. The extract administered orally produced similar signs without the abdominal constriction and convulsions (median lethal oral dose = 6.73 mg/kg). Gross pathology findings included extensive and severe congestion of the abdominal visceral organs. Vehicle control mice were normal. In conclusion, G. monilata, previously reported as nontoxic in homeotherms, yields an extract which contains a water soluble glycosidic substance(s) which is lethal to mice.