Bioassays of APONIN-3 and -4 with rabbit erythrocytes

Rabbit erythrocytes in methanolic phosphate medium were used to bioassay the activity of authentic samples of methyl stearate and methyl palmitate (in 10% methanol:90% water, v/v), which had been identified as apparent oceanic naturally occurring cytolins (APONIN-3 and -4) produced by Nannochloris oculata. The two natural products are notable for cytolytic activity toward the unarmoured dinoflagellate, Gymnodinium breve Davis, an organism responsible for red tides consisting of harmful algal blooms in the Gulf of Mexico and along the eastern coast of the United States. Bioassays were done with heparinized rabbit blood. The absorbance at 540 nm was observed for 15 min in comparison with a sample treated with haemolysing agent. The results indicated that at reasonable concentrations of 1-10 ppm, neither was a haemolysin, although such concentrations caused cytolysis of G. breve cultures.