Abstract
In order to isolate dinoflagellate growth inhibitor (DGI) which was indicated to distributes broadly in the sediments of Ariake and Hakata Bays, the acetone extract was prepared form the sediment of the most eutrophicated point in Hakata Bay. The extract was separated into two fractions of tar and sulfur. The tar was fractionated into nine fractions by TLC and the sulfur into ether solubles and insolubles. The mortal effects of these fractionated compounds were checked by bioassay employing five species of dinoflagellates. Among nine fractions, the fifth fraction showed the lowest lethal concentrations to be 2 and 8ppm for Peridinium trochoideum and Peridinium sp., the sixth fraction to be 1ppm for Gymnodinium breve and the third fraction to be 0.25 and 0.03ppm for Gymnodinium nagasakiense and Heterocapsa triquetra, respectively. In order to know the distribution of DGI in these nine fractions, quotients were obtained by divid-ing their yields with their lowest lethal concentrations for every species of dinoflagellates used and expressed as percentage to that of the original acetone extract applied. DGI was revealed to be most abundant in the fifth fraction. Then, DGI was isolated from the fifth fraction. The fifth fraction was purified by subjecting it to columnchromatography. Then, DGI was isolated. Thes DGI killed Chattonella antiqua at 0.0625ppm, Chattonella marina at 0.5ppm, Gymnodinium breve at 0.25ppm, Gymnodinium nagasakiense at I ppm, and Peridinum trochoideum at 0.25 ppm. These results together with the distribution of DGI in the sediments as shown in the previous paper tell us that DGI might control the emergence of phytoflagellate red tides in Ariake Bay.