Pseudopterosin biosynthesis in Symbiodinium sp., the dinoflagellate symbiont of Pseudopterogiorgia elisabethae

Investigations are reported that identify the biosynthetic source and origins of the pseudopterosins, pharmacologically important diterpene glycosides, in the gorgonian coral Pseudopterogorgia elisabethae. We report here the isolation of physiologically significant levels of endogenous; pseudopterosins A, B, C, and D from purified symbionts identified as the dinoflagellate Symbiodinium sp. Biosynthetic studies in photosynthesizing symbiont isolates utilizing C-14-labeled inorganic carbon and the tritiated intermediate geranylgeranyl diphosphate yielded radiochemically pure pseudopterosins A through D and the first committed intermediate, elisabethatriene. The (CO2)-C-14 uptake into the pseudopterosin pathway occurred at low levels compared to the (CO2)-C-14 uptake into total lipids, suggesting a large reserve pool of the compounds. These results reveal for the first time that pseudopterosin biosynthesis is occurring within the algal symbiont and suggests the physiological implications of this biosynthesis.