Chemical and biological studies of the symbiosis between a marine sponge and a cyanobacterium

Chapter 1 of this dissertation is an introduction to the biology of sponges and in particular to the phenomenon of symbiosis in marine sponges. The secondary metabolism of the tropical dictyoceratid sponge Dysidea herbacea (Keller) is reviewed.; Chapter 2 of this dissertation describes the isolation and structural elucidation of a series of new polychlorinated compounds, the dysideathiazoles (53-55, 61, and 62) and dysideapyrrolidone (63), from D. herbacea. The absolute configuration of the dysideathiazoles was determined by single-crystal X-ray diffraction analysis of a bromophenylcarbamate derivative to be S at all chiral centers.; The dominant prokaryotic symbiont of Dysidea herbacea is the filamentous cyanobacterium Oscillatoria spongeliae (Schulze). Chapters 3 and 4 of this dissertation experimentally address the question of whether the cyanobacterium plays a role in the biosynthesis of the polychlorinated or polybrominated secondary metabolites that can be isolated from the intact sponge-cyanobacterial association. This research was based on the rationale that, if a compound is shown to be localized exclusively in a single cell type, then it is highly likely to have been produced by that cell.; This was tested on a glutaraldehyde-fixed cell preparation from a specimen of Dysidea herbacea containing both sesquiterpenes and polychlorinated metabolites. The cyanobacterium was separated from the sponge cells by flow cytometry, using phycoerythrin fluorescence as the sorting parameter. Chemical analysis of the different cell populations demonstrated conclusively that the polychlorinated metabolite 13-demethylisodysidenin (29) was limited to the cyanobacterial filaments, whereas the accompanying sesquiterpenes herbadysidolide (1) and spirodysin (2) were found exclusively in the sponge cells.; A similar study involved a specimen of Dysidea herbacea that contained a polybrominated biphenyl ether and no sesquiterpenes. The brominated metabolite, which made up 6% of the sponge's dry weight, was found to accumulate as crystalline material in the sponge tissue. Flow cytometric sorting followed by chemical analysis demonstrated that the brominated compound was also localized in the cyanobacterial filaments.; The experiments described in Chapters 3 and 4 provide the first experimental evidence that a microbial symbiont is responsible for the biosynthesis of secondary metabolites found in a sponge. Chapter 5 summarizes the distribution of secondary metabolites in Dysidea herbacea, and discusses other cases of circumstantial evidence for symbiont biosynthesis of natural products isolated from marine sponges.