**4. Conclusions**

We established that the Easter Island sea anemone *Gyractis sesere* contained two anthraquinones, Lupinacidin A (**1**) and Galvaquinone B (**2**), which were ultimately found to be produced by one of the Actinobacteria associated with this marine invertebrate, *Verrucosispora* sp. SN26\_14.1. The production of the identified metabolites by the bacterial isolate apparently follows a recently characterized PKS type II pathway with a Baeyer−Villiger type rearrangemen<sup>t</sup> assembly line. Our finding adds a new actinobacterial genus to the producers of these anthraquinones, implying that these metabolites are not exclusive to the genera *Streptomyces* and *Micromonospora*. It was demonstrated, that culture-based approaches remain as effective tools for the isolation of polyketide producing Actinobacteria as sources for secondary metabolites of potential use in drug discovery. Our study confirms that cnidarians, and in specific sea anemones, can be a source of such pharmacologically relevant microorganisms. Finally, these findings re-open the debate about the real producers of secondary metabolites in sea animals and add another example of associated bacteria as producers of substances present in sea animals. In addition, the study provides information on the chemistry harbored in biota of the geographically isolated and almost unstudied, Easter Island.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1660-3397/17/3/154/s1. Information on NMR spectra, HRLCMS data, and secondary metabolite gene cluster.

**Author Contributions:** I.S., J.F.I. and J.W. planned the experiments, I.S. performed the experiments, analyzed and evaluated the data and wrote the first draft of the publication. J.F.I., F.D.S. and J.W. supervised the work and revised the manuscript. S.K. sequenced the genome and supplied the genome data. M.L. and N.P. acquired LCMS and NMR data. F.D.S. acquired and analyzed NMR data.

**Funding:** We thank the Deutscher Akademischer Austauschdienst (DAAD) for financial support under the stipend # PKZ91564794. We acknowledge financial support by the Land Schleswig-Holstein within the funding programme Open Access Publikationsfonds.

**Acknowledgments:** We thank Marion Höftmann and Gitta Kohlmeyer-Yilmaz for her valuable help with the NMR data acquisition. We thank Ute Hentschel Humeida (GEOMAR Helmholtz Centre for Ocean Research Kiel) for her support. We also thank Philip A. Thomas (ImagesByPT@PhilipT.com), for providing high quality photography of the sea anemone *Gyractis sesere*. I.S. thanks Millaray Sierra for her support during the research. N.P. thanks the Deutsche Bundesstiftung Umwelt (German Federal Environmental Foundation) for a predoctoral fellowship.

**Conflicts of Interest:** The authors declare no conflict of interest.
