Toxicity to mice and sheep of a bloom of the cyanobacterium (blue-green alga) Anabaena circinalis

Saxitoxin, a toxic marine natural product that targets a multitude of receptors

Saxitoxin (STX) was discovered early last century and can contaminate seafood and drinking water, and over time has become an invaluable research tool and an internationally regulated chemical weapon. Among natural products, toxins obtain a unique reputation from their high affinity and selectivity for their target pharmacological receptor, which for STX has long been considered to only be the voltage gated sodium channel. In recent times however, STX has been discovered to also bind to calcium and potassium channels, neuronal nitric oxide synthase, STX metabolizing enzymes and two circulatory fluid proteins, namely a transferrin-like family of proteins and a unique protein found in the blood of pufferfish.

Toxin-Producing Anabaena flos-aquae Induces Settling of Chlamydomonas reinhardtii, a Competing Motile Alga

Toxin production is an adaptation that allows cyanobacteria in resource-limiting environments to ameliorate the effects of herbivory and competition with other phototrophs. We demonstrate that the cyanobacterial toxins anatoxin-a and microcystin-LR paralyze the motile green alga Chlamydomonas reinhardtii. In addition, both purified toxins and cyanobacterial extracellular products containing these toxins cause the alga to settle faster than in nontoxic media. In microcosm experiments, the presence of either the cyanobacterium or its extracellular products induce settling in the alga, similar to the response observed with the addition of both anatoxin-a and microcystin-LR. The cyanobacterial production of paralyzing toxins represents a novel mechanism for phytoplankton settling. This prokaryotic/eukaryotic chemical interaction may create a competitor-free zone for cyanobacteria in lake environments, predicating optimal conditions for a toxic cyanobacterial bloom.

The first evidence of paralytic shellfish toxins in the fresh water cyanobacterium Cylindrospermopsis raciborskii, isolated from Brazil

The blooms of toxic cyanobacteria (blue-green algae) are causing problems in many countries. During a screening of toxic freshwater cyanobacteria in Brazil, three strains isolated from the State of Sao Paulo were found toxic by the mouse bioassay. They all were identified as Cylindrospermopsis raciborskii by a close morphological examination. Extracts of cultured cells caused acute death to mice when injected intraperitoneally after developing neurotoxic symptoms which resembled to those caused by paralytic shellfish toxins. The analysis of the sample by HPLC-FLD postcolumn derivatization method for paralytic shellfish toxins resulted in the detection of several saxitoxin analogs. To avoid being misled by false peaks, the sample was reanalyzed after purification and also under the different postcolumn derivatizing conditions. Finally, the newly developed LC-MS method for paralytic shellfish toxins was applied to unambiguously identify the toxins. One isolate produced neosaxitoxin predominantly with saxitoxin as a minor component. The other two showed identical toxin profiles containing saxitoxin and gonyautoxins 2/3 isomers in the ratio of 1:9. This is the first evidence of paralytic shellfish toxins in this species and also the occurrence of the toxin producing cyanobacterium in South American countries.

The toxicity of cyanobacterial toxins in the mouse: I microcystin-LR

Blooms of cyanobacteria or blue-green algae are known to have caused poisoning in fish, waterfowl, animals and man. One of the toxins responsible for this is the hepatotoxin microcystin-LR which has been found to occur in blooms present intermittently in sources used for domestic water supplies. Three sets of experiments were undertaken to investigate the acute toxicity of microcystin-LR in mice and rats by the oral and intraperitoneal routes, the potential for effects on foetal development in the mouse, and the effects of repeated oral dosing over 13 weeks in the mouse. The results of this work were as follows: (1) Microcystin-LR is 30-100 times less toxic via oral ingestion than via intraperitoneal injection; (2) Microcystin-LR is not a selective developmental toxicant in the mouse. There was a No Observed Adverse Effect Level (NOAEL) of 600 microg kg(-1) bodyweight per day given on days 6-15 of pregnancy for any form of developmental toxicity; (3) There was a clear NOAEL for tissue damage in the liver of 40 microg kg(-1) bodyweight per day of microcystin-LR. Using this data, a value of 1 microg l(-1) microcystin-LR would be an appropriate guideline value for drinking water.

Sheep mortality associated with paralytic shellfish poisons from the cyanobacterium Anabaena circinalis

This is the first report of sheep mortalities associated with paralytic shellfish poisons (PSPs) from the cyanobacterium Anabaena circinalis Rabenhorst. Fourteen sheep died within 150 m of a farm dam containing a dense bloom of A. circinalis. Extracts from both the cyanobacterium and small intestine from a dead ewe were analysed by high-performance liquid chromtography (HPLC) and found to contain PSPs. The toxin profiles of the cyanobacterium contained a high proportion of C-toxins (70%), whereas toxins in the small intestine content were dominated by gonyautoxin 5 (87%). This observation could be explained by desulfation of the C-toxins in the gut of the sheep. The LD100 of bloom material calculated from HPLC data was consistent with mouse bioassay data (12-25 mg/kg). The symptoms of affected sheep, mouse bioassay data, coupled with HPLC analysis of toxins from the bloom samples and the intestine contents, and the absence of other cyanobacterial alkaloid toxins, indicate that PSPs were responsible for the deaths of the sheep.

Bioaccumulation of paralytic shellfish poisoning (PSP) toxins from the cyanobacterium Anabaena circinalis by the freshwater mussel Alathyria condola

The Australian freshwater mussel Alathyria condola accumulated high levels of paralytic shellfish poisoning (PSP) toxins when fed the neurotoxic cyanobacterium Anabaena circinalis, shown recently to contain high concentrations of C-toxins and gonyautoxins. Significant accumulation (>80 mu g/100 g of mussel flesh) was detected following 2-3 exposure to water containing 2 x 105 cells/ml A. circinalis. Only trace accumulation of PSP toxins was demonstrated over long-term (5 week) exposure at low concentration (c. 104 cells/ml). The relative abundance of C-toxins, gonyautoxins and saxitoxins in mussels generally matched the toxin profiles of the dietary A. circinalis, although there were differences in the GTX2/3 and C1/2 ratios with time, and an increase in abundance of decarbamoylgonyautoxins. Analysis of mussel tissues after 7 days, exposure to A. circinalis revealed that 96% of the toxins were accumulated in the viscera. As in marine waters, the bioaccumulation of PSP toxins in freshwater mussels may pose a health risk to humans and animals, especially in areas where seasonally decreasing water levels expose mussel beds to surface scums of toxic cyanobacteria.

Protein phosphatase activity in cyanobacteria: consequences for microcystin toxicity analysis

Hepatotoxic microcystin levels in cyanobacteria (blue-green algae) were assessed by an assay based on inhibition of protein phosphatases type 1 (PP1) and type 2A (PP2A) in crude chicken forebrain extracts using 32P-labelled glycogen phosphorylase as substrate. While cyanobacteria are reported to be devoid of phosphorylase phosphatase activity, two samples obtained from cyanobacterial scums, containing predominantly Anabaena circinalis, were found to contain high levels of a phosphorylase phosphatase activity which completely masked the presence of microcystin. Furthermore, samples containing predominantly Microcystis aeruginosa but increasing Anabaena circinalis contained sufficient phosphorylase phosphatase activity to cause a fourfold underestimation of microcystin levels. Thus, protocols for microcystin toxicity analysis should take into account the possible presence of endogenous phosphatase activity, thereby preventing underestimation of toxin levels.

Effect of route of exposure and repeated doses on the acute toxicity in mice of the cyanobacterial nicotinic alkaloid anatoxin-a

Anatoxin-a (ANTX-a) is a potent nicotinic cholinergic alkaloid produced by some toxigenic strains of cyanobacteria. We have examined i.p. and oral LD50 values of two ANTX-a producing Anabaena sp. and synthetic (+)-ANTX-a in outbred Swiss Webster mice. All three appeared equivalent by i.p. injection, but Anabaena flos-aquae NRC-44-1 was approximately twice as potent orally as the other two. Additionally, we were unable to demonstrate development of any biologically significant tolerance to acute ANTX-a exposure using two different repeated dose regimens.