The effects of the diarrhetic shellfish poisoning toxins, okadaic acid and dinophysistoxin-1, on the growth of microalgae

The diarrhetic shellfish poisoning toxins okadaic acid (OA) and dinophysistoxin-1 (DTX-1) are potent phosphatase inhibitors produced by certain species of marine dinoflagellates. OA can cause hyperphosphorylation of a broad range of animal and higherpalnt proteins, but little is known regarding the effects of the DSP toxins on marine organisms or their biological function. A variety of microalgae, including a clone ofProrocentrum lima known to produce both OA and DTX-1, were incubated with solutions of OA and in one case DTX-1 or a combination of OA and DTX-1. OA inhibited the growth of all non-DSP-producing test species at micromolar concentrations, butP. lima was not affected even at much higher levels. This differential activity of OA suggests that the DSP toxins may play an allelopathic role and raises questions regarding the strategies adopted by DSP-producing dinoflagellates such asP. lima to avoid autotoxicity. The effects of DTX-1 on microalgal growth were found to be equivalentt to those of OA, and the effects of both toxins in combination were simply additive.