Stimulators of Gambierdiscus toxicus (Dinophyceae) growth:: the possible role of gambieric acid-A as an endogenous growth enhancer

The effects on the growth of Gambierdiscus toxicus Adachi et Fukuyo (Dinophyceae) cultures by conditioned media from dense-growing cultures were examined and enhanced growth was observed. The increase in Gambierdiscus toxicus cell concentration with the addition of the conditioned media suggested the existence of endogenously produced growth enhancer(s). Gambieric acid-A, a polyether compound, is known to be excreted by G. toxicus, therefore we examined the effects of gambieric acid-A of G. toxicus growth. The growth of G. toxicus clones responded maximally at 1.89 nM gambieric acid-A. Gambierdiscus toxicus growth followed a dose-dependent saturation curve with inhibition at 18.9 nM gambieric acid-A. The results of this study strongly suggest the potential biological function of gambieric acid-A to be an endogenous growth enhancer of G. toxicus. To our knowledge, no endogenously produced factor(s) enhancing the growth of any dinoflagellate have been reported.