Ascidian-associated photosymbionts from Manado, Indonesia: secondary metabolites, bioactivity simulation, and biosynthetic insight

This research work aimed at investigating the chemistry and biosynthetic potential of ascidian-associated symbionts that originated from Manado Bay, North Sulawesi. We initially enriched the symbiotic cells associated with the Manadonese ascidian Lissoclinum patella . Subsequently we identified the presence of Prochloron didemni in both unenriched and salt-enriched samples by examining the 16S rRNA gene and the chlorophyll A oxygenase (CAO) gene. Investigation of the secondary metabolites by HPLC, LCMS/MS, and NMR showed the presence of ulithiacyclamide along with patellamide E in the unenriched symbiotic cells. Interestingly, ulithiacyclamide was detected in the enriched cells from the same Ascidian specimen. Molecular docking showed the high binding affinity of both compounds to estrogen receptor beta (ER-β) protein. This is a subtype of the nuclear receptor superfamily expressed abnormally in ovarian cancer cells. Furthermore, we isolated a patE gene variant encoding for a precursor with patellamide E (VTVCITFC) and ulithiacyclamide (CTLCCTLC) core peptides from the enriched cells. This represents a new core peptide combination. The outcome of this work provides a basis for producing useful cyclic peptides, in sustainable way, through symbiont cultivation. This could become a platform for bioengineering to generate diverse compound analogues.