Analysis of the production of compounds of biomedical interest from symbiont microalgae cultures

Abstract

The genus Zoanthus has been studied over the years due to new incorporations of bioactive compounds with great pharmacological potential, such as the zoanthaminealkaloid family, secondary metabolites with a novel chemical structure. The complexity of the biosynthesis of these compounds may be due to the peculiar relationship that the coral establishes especially with the genus Symbiodinium sp. To evaluate the capacity of the symbiont zooxanthellae ad bacterial to biosynthesise alkaloids, the chemical profiles of the extracts from the coral Z. pulchellus and the dinoflagellate Symbiodinium sp. isolated from it, as well as extracts from the laboratory culture enriched with different carbon sources (glucose, glycerol, and sodium acetate) of Symbiodinium sp., were analysed by HPLC-UV/DAD. The result was the isolated and identification of two major compounds, zoanthamine and norzoanthamine only in Symbiodinium sp. cells isolated from field-collected coral and from the zoanthid itself. We observed a change in the behaviour of the symbiont reflected in the chemical composition of the profiles when it is cultured in the laboratory, including in cultures enriched with carbon sources, without successfully achieving the presence of the desired alkaloids and cell growth. To rule out any involvement of other symbiont organisms, 3 bacterial colonies of zooxanthellae, identified as Marinobacter sp., Pseudoalteromonas sp., Labrenzia sp. were isolated, cultured, and co-cultured. These were negative for the presence of alkaloid, but in comparison, changes in chemical profiles suggested by the interaction of zooxanthellae with bacteria in co-culture were also observed. The analyses were supported by H-RMN and Dragendorff revealed TLC tests that qualitatively reflected the existence of alkaloids in the enriched Symbiodinium sp. cultures, although no target metabolite was isolated. Therefore, it is possible that these symbiotic microalgae may have a precursor role in the biosynthesis of future metabolites. Ultimately, this study provides information on the scarce literature covering the unresolved debate: the real involvement of symbiotic organisms in marine natural products and to shed light on the origin of zoanthamine alkaloids.