Water blooms formed by potentially toxic species of cyanobacteria are a common phenomenon in the Baltic Sea in late summer. Twenty-five cyanobacterial bloom samples were collected from open and coastal waters of the Baltic Sea during 1985 to 1987, and their toxicity was determined by mouse bioassay. All of 5 bloom samples from the southern Baltic Sea, 6 of 6 from the open northern Baltic Sea (Gulf of Finland), and 7 of 14 Finnish coastal samples were found to contain hepatotoxic cyanobacteria. Nodularia spumigena and Aphanizomenon flos-aquae occurred together in high amounts in blooms from the open-sea areas. In addition, coastal samples contained the species Anabaena lemmermannii, Microcystis aeruginosa, and Oscillatoria agardhii. Eighteen hepatotoxic N. spumigena cultures were isolated from water bloom and open-sea water samples. High-pressure liquid chromatographic analysis of both hepatotoxic bloom samples and Nodularia strains showed a single toxic fraction. The toxin concentrations of the blooms were .2.4 mg/g of freeze-dried material, and those of laboratory-grown cultures were 2.5 to 8.0 mg/g of freeze-dried cells. A single toxin was isolated from three N. spumigena-containing bloom samples and three N. spumigena laboratory isolates. Amino acid analysis and lowand high-resolution fast-atom bombardment mass spectroscopy indicated that the toxin from all of the sources was a cyclic pentapeptide (molecular weight, 824) containing glutamic acid, I-methylaspartic acid, arginine, N-methyldehydrobutyrine, and 3-amino-9-methoxy-2,6,8-trimethyl-10-phenyl-4,6-decadienoic acid. This indicates that the Baltic Sea toxin is nodularin, the cyclic pentapeptide produced by field and laboratory-cultured N. spumigena previously reported from New Zealand brackish water lakes. The signs of poisoning by the pentapeptide were similar to those reported for the heptapeptide toxins from other cyanobacteria.
A bioassay for the detection of neuro‐ and hepatotoxins of cyanobacteria was developed. Larvae of a small shrimp, Artemia salina, were used as the test organism. Two pure toxins, 44 natural bloom samples, and 29 laboratory strains of cyanobacteria were studied. The toxicity of the samples had earlier been tested by mouse bioassay and in most cases by chemical analysis of the toxins. Moderate and high concentrations of toxins in bloom samples can be reliably detected by the Artemia salina method. Out of 29 toxic bloom samples, 4 were found nontoxic to Artemia. According to mouse bioassay, the toxicity of these samples was very low. The pure laboratory‐grown strains contained some compounds that were toxic to A. salina but nontoxic to mouse. Because of these compounds, 1 out of 15 nontoxic bloom samples was erroneously analyzed to be toxic. EC50 for hepatotoxin desmethyl 7‐microcystin‐RR was 5.0 μ/mL. Pure anatoxin‐a‐hydrochloride was not toxic to larvae, but when added to nontoxic cyanobacterial samples, anatoxin‐a was toxic.
To study toxicity of 76 laboratory‐grown strains of planktonic cyanobacteria to mosquito larvae, hydrophilic and lipophilic cell‐free extracts of cyanobacteria were incubated with larvae of the Aedes aegypti mosquito and death percentages were followed during 2 days. Toxicity was clearly associated with hepato ‐ and neurotoxins of the samples. A strain of Microcystis aeruginosa was most effective, and caused death of the larvae due to a single hepatotoxin. Pure mammalian neurotoxin, anatoxin‐a, was also toxic, and probably acted as a neurotoxin with the mosquito larvae.
It was found that Oscillatoria agardhii strain 27 produced compounds toxic against mosquito larvae (Aedes albopictus), therefore, these compounds were extracted and separated for insecticide development. Structural characterization of the toxic fraction by 1H‐NMR and GC‐MS showed that these compounds are not the neurotoxins or hepatotoxins conventionally produced by Oscillatoria, but it contained a mixture of unsaturated fatty acids, oleic, linoleic, and γ‐linolenic acids, as well as saturated fatty acids, myristic, palmitic, and stearic acids. In a bioassay developed for these hydrophobic compounds using mosquito larvae, authentic unsaturated fatty acids were shown to be toxic, whereas saturated ones were not active. The results suggested that it might be possible to use unsaturated fatty acids as environmentally safe and effective insecticides without the side effects of the chemically synthesized insecticides. © 2000 John Wiley & Sons, Inc. Environ Toxicol 15: 114–119, 2000
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