Characterisation of Saxitoxins Produced by the Cyanobacterial Genus Anabaena in Australia

This report was produced for the Urban Water Research Association of Australia, a now discontinued research program.

Back to the Urban Water Research Association of Australia catalogue

Characterisation of Saxitoxins Produced by the Cyanobacterial Genus Anabaena in Australia

Report no. UWRAA 135

1998

Synopsis

Anabaena circinalis is one of the major bloom-forming of cyanobacteria in Australian rivers and water storages. This species can impair the quality of water used for drinking, domestic supplies, agriculture, and recreation by the production of neurotoxins, which have been identified as saxitoxins (STXs).

In this study, geographic patterns of occurrence and composition of STXs were investigated by screening both naturally occurring field samples and isolates Of Anabaena and Aphanizomenon cultivated under identical growth conditions. STXs were detected by High Performance Liquid Chromatography (HPLC) in approximately 60% Of all field samples and strains Of A. circinalis. A maximum total STX concentration of approximately 4500 pg g-l dly wt. cellular material and a maximum relative STX concentration of 723 pg STX equivalents dry wt. cellular material was detected.

The major components of positive samples were the C-toxins (Cl and C2) and the gonyautoxins (GTX2 and GTX3), while saxitoxin (STX), GTX5 and the decarbamoyl gonyautoxins (dcGTX2 and dcGTX3) were present as minor constituents. Apart from the unique toxin profile found in a geographically isolated strain originating from Western Australia, there were no recognisable differences in toxin composition throughout Australia’s major drainage divisions. Temporal changes in toxin levels and composition in both natural samples and cultured strains would appear to account for the observed variability in all samples. The hydroxy toxins GTXI and GTX4 and neo STX, previously identified in marine dinoflagellates, were not detected in any sample or cultured strain of Anabaena.

No concluding evidence was found to suggest that other species of Anabaena or Aphanizomenon spp. in Australia produce STXs. The neurotoxin anatoxin-a and hepatotoxin microcystin were not detected in species of Anabaena in Australia. Experimental studies with a single strain of A. circinalis were undertaken in the laboratory to examine the effect of different nitrogen sources and concentrations of nitrate on growth and STX levels. A linear relationship between cell density and total STX concentrations (intracellular + extracellular) was demonstrated in all experiments. The proportion of extracellular toxin increased as cultures aged. Treatment with ammonium and high nitrate levels promoted toxin release into the medium. Total toxin content and relative toxin content of A. circinalis cells may vary with the nitrogen source, nitrate concentration and with the age of the culture.

Back to the Urban Water Research Association of Australia catalogue