The localization of bioactive secondary metabolites in sponges, ascidians and their associated symbionts

The focus of this dissertation is twofold: the secondary metabolites of sponges and ascidians, and the localization of bioactive compounds in invertebrates and their associated symbionts. Although many marine secondary metabolites isolated from invertebrates are attributed to production by associated microbes, this has rarely been demonstrated. One method of studying the biosynthetic sources of natural products is to localize compounds in specific cells of the host or symbiont. Knowledge of the location of bioactive metabolites may help future culturing efforts of the invertebrates and/or symbionts to provide a more efficient source of compounds. This knowledge can also help increase our understanding of the potential biological and ecological roles of secondary metabolites in symbiotic associations.; The first chapter introduces the chemistry of sponges and ascidians that has been ascribed to symbionts and reviews literature examples of localization studies. Chapter 2 describes the relative and absolute stereochemistry of the unusual heptaprenoid compounds didemnaketals A and B isolated from an ascidian. Chapter 3 reports the isolation and structure elucidation of a new pyridoacridine from the sponge Oceanapia sagittaria.; The second section of the thesis begins with early projects that involved physical methods to localize compounds and progresses to recent studies incorporating molecular approaches. Chapters 4 and 5 describe the localization of secondary metabolites in the sponge Oceanapia sagittaria and ascidian Lissoclinum patella using chemical techniques. In both studies, the secondary metabolites were located in host cells and tissues and not in associated microbes. The work in chapters 6 and 7 involved a combination of physical methods and molecular techniques to localize compounds in ascidian larvae and sponges, to search for potential symbiotic sources and to examine the microbial diversity of the invertebrates. The overall conclusion of the localization studies is that general hypotheses regarding symbiont production of secondary metabolites are often unfounded and that each case requires an individual study. The combination of physical and chemical techniques together with molecular approaches are necessary to determine the biosynthetic source of metabolites and to gain a better understanding of the microbial diversity of invertebrates and the potential ecological and biological roles of compounds in symbiotic associations.