Characterisationof Saxitoxins Produced by the Cyanobacterial Genus Anabaena in Australia
ReportNo WSAA 135
Inthis study, geographic patterns of occurrence and composition of STXs wereinvestigated by screening both naturally occurring field samples and isolatesof Anabaena and Aphanizomenon cultivated under identical growth conditions. STXswere detected by High Performance Liquid Chromatograph (HPLC) in approximately60% of all field samples and strains of A.circinalis. A maximum total STX concentration of approximately 4500
Themajor components of positive samples were the C-toxins (C1 and C2) and thegonyautoxins (GTX2 and GTX3), while saxitoxin (STX), GTX5 and the decarbomyolgonyautoxins (dcGTX2 and dcGTX3) were present as minor constituents. Apart fromthe unique toxin profile found in a geographically isolated strain originatingfrom Western Australia, there were no recognisable differences in toxincomposition throughout Australia’s major drainage divisions. Temporal changesin toxin levels and composition in both natural samples and cultured strainswould appear to account for the observed variability in all samples. Thehydroxy toxins GTX1 and GTX4 and neoSTX, previously identified in marinedinoflagellates, were not detected in any sample or cultured strain of Anabaena.
No concludingevidence was found to suggest that other species of Anabaena or Aphanizomenonspp. in Australia produce STXs. The neurotoxin anatoxin-a and hepatotoxinmicrocystin were not detected in species of Anabaenain Australia.
Experimentalstudies with a single strain of A.circinalis were undertaken in the laboratory to examine the effect ofdifferent nitrogen sources and concentrations of nitrate on growth and STXlevels. A linear relationship between cell density and total STX concentrations(intracellular + extracellular) was demonstrated in all experiments. Theproportion of extracellular toxin increased as cultures aged. Treatment withammonium and high nitrate levels promoted toxin release into the medium. Totaltoxin content and relative toxin content of A.circinalis cells may vary with the nitrogen source, nitrate concentrationand with the age of the culture.
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