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 Tunicata, Mollusca and Cnidaria) caused some to speculate that they were produced by associated symbionts. We tested this hypothesis by localizing specific metabolites in cells using a combination of visualization methods, including laser-scanning confocal, epifluorescence, and transmission electron microscopy, as well as cell-separation techniques, and chemical analysis. This study demonstrates that large quantities of the pyridoacridine alkaloid dercitamide (=Kuanoniamine C) are localized exclusively in bacteria-free sponge cells in the marine sponge Oceanapia sagittaria (Sollas), and are probably not produced by intracellular symbiotic organisms. We hypothesize that it is unlikely that the pyridoacridines are produced by extracellular bacteria and then transferred to specific sponge cells. The localization of dercitamide in significant concentrations in specific cells throughout the sponge suggests important biological and ecological functions, such as chemical defense against predators and possibly microbial pathogens. If pyridoacridines are produced by the host organism in other phyla, this may be a case of convergent evolution of an efficient and useful biosynthetic pathway.