Studies on the production of bioactive metabolites by marine microalgae

A free-swimming dinoflagellate, Amphidinium operculatum var. gibbosum, strain S1-36-5, was previously reported to produce a series of antitumor metabolites, amphidinolides. In this dissertation research, the chemical profiles of the cells from different cultures were examined. The results showed that large amounts of amphidinolide B were found only in the older cells (17 days old). However, relatively large amounts of caribenolide 1, the most potent antitumor macrolide found in this species, were also found in the younger cells (7 days old). This result indicated that caribenolide I can be produced in a more efficient way (e.g. continuous culture). Four major cytotoxic compounds, amphidinolides B, G, H and caribenolide I, were isolated from the cells harvested from a semi-continuous culture by chromatography and characterized by spectroscopic techniques. Amphidinolide G was isolated for the first time from A. operculatum var. gibbosum . In contrast, no amphidinolide was isolated from the cells of a 15,000 liter culture. Two lipid compounds were isolated from the second batch of culture, and their bioactivity is under investigation. The low content of the secondary metabolites in 15,000 liter culture was thought to be due to the culture conditions, such as the light deficiency and the nutrient composition changes caused by the contaminants. Studies on the production of extracellular metabolites of Pseudo-nitzschia multiseries indicated that the production of domoic acid depended on the age of the culture. The organism in the older culture seemed to release more domoic acid into the medium rather than keeping it in the cells. A novel extracellular metabolite, bacillariolide III, was isolated from the culture medium, and the structure was determined by NMR, IR, MS and UV-vis. The structure of bacillariolide III was related to bacillariolide I, a phospholipase A 2 inhibitor, previously isolated from the cells of the same organism. The biosynthetic relationship of the two metabolites was proposed. A preliminary experiment indicated that bacillariolide III seemed to stimulate the growth of another diatom Skeletonema costatum. In addition, experiments were carried out as part of the ongoing studies on the biosynthesis of amphidinolides and domoic acid, and the results were discussed