Isolation and characterisation of photoactive haemolytic toxin from Heterocapsa circularisquama

Abstract

Red tides of Heterocapsa circularisquama, identified as a new species of dinoflagellate a few years ago, have frequently caused mass mortality of several species of bivalve in Japan, whereas no harmful effects on fish have been reported so far. We found that cell-free methanol extract from H. circularisquama caused haemolysis of rabbit erythrocytes and showed cytotoxic effects on HeLa cells and on the rotifer Brachionus plicatilis in a dose- and time-dependent manner. Interestingly, the haemolytic activity and cytotoxic effects of the extract were completely dependent on the presence of light, and no such bioactivities were observed in the dark even at very high concentrations of the extract. The maximum activity was attained at 420nm. These results suggest that H. circularisquama has a photosensitising haemolytic toxin. Highly purified toxin was obtained after several purification procedures including gel-filtration, thin-layer chromatography and reverse-phase high-performance liquid chromatography. The absorption spectrum of this purified toxin in dimethyl sulfoxide showed peaks at 450nm, 590nm and 640nm.

Keywords:

• CYTOTOXICITY
• HAEMOLYTIC TOXIN
• HETEROCAPSA CIRCULARISQUAMA
• PHOTOSENSITISER
• RED TIDE