The cellular localization of dercitamide in the Palauan sponge Oceanapia sagittaria

The isolation of a class of bioactive aromatic alkaloid compounds known as pyridoacridines from members of four phyla (Porifera, Chordata-Subphylum Tu nicata, Mollusca and Cnidaria) caused some to speculate that they were prod uced by associated symbionts. We tested this hypothesis by localizing speci fic metabolites in cells using a combination of visualization methods, incl uding laser-scanning confocal, epifluorescence, and transmission electron m icroscopy, as well as cell-separation techniques, and chemical analysis. Th is study demonstrates that large quantities of the pyridoacridine alkaloid dercitamide (= Kuanoniamine C) are localized exclusively in bacteria-free s ponge cells irk the marine sponge Oceanapia sagittaria (Sollas), and are pr obably not produced by intracellular symbiotic organisms. We hypothesize th at it is unlikely that the pyridoacridines are produced by extracellular ba cteria and then transferred to specific sponge cells. The localization of d ercitamide in significant concentrations in specific cells throughout the s ponge suggests important biological and ecological functions, such as chemi cal defense against predators and possibly microbial pathogens. If pyridoac ridines are produced by the host organism in other phyla, this may be a cas e of convergent evolution of an efficient and useful biosynthetic pathway.