Sequestration and Cyanobacterial Diet Preferences in the Opisthobranch Molluscs Dolabrifera nicaraguana and Stylocheilus rickettsi

Abstract

A multidisciplinary approach was used to assess chemical ecological dietary interactions between marine organisms as a tool to isolate novel ecologically relevant compounds with biotechnological potential. First, laboratory-based feeding preference assays of the sea hareDolabrifera nicaraguana(previously known asD. dolabrifera), an anaspidean mollusc, were conducted by simultaneously offering six food options collected from nearby tidal pools in the Coiba National Park in the Tropical Eastern Pacific of Panama. An evaluation of preferred dietary repertoire revealedD. nicaraguanasignificantly preferred cf.Lyngbyasp. over the cyanobacteriumSymplocasp., green algaChaetomorphasp., and red algaSpyridiasp. A no-choice feeding assay using cf.Lyngbyasp. or green algaCladophorasp. supported this finding. Secondly, we conducted bioactivity-guided fractionation using the preferred food source ofD. nicaraguana, the ‘hair-like” cf.Lyngbyasp. from which we also isolated and elucidated two new depsipeptide compounds, veraguamide M (1) and veraguamide N (2). Veraguamides M (1) and N (2) showedin vitroactivity toward the malaria-causing parasitePlasmodium falciparumwith GI50values of 4.2 and 4.3 μM, respectively, and therapeutic windows of 7.0–8.0 (based on moderate cytotoxicities to mammalian Vero cells with GI50values of 29.3 and 34.1 μM, respectively). Veraguamide N (2) was also active againstLeishmania donovani, the causative agent of visceral leishmaniasis, with a GI50value of 6.9 μM. We then evaluated sequestration of these new compounds byD. nicaraguanaused in the feeding assays and found trace amounts of the dietary sequestered compounds. Finally, we evaluated sequestration of these new compounds by the sea hareStylocheilus rickettsi(previously known asS. striatus) that were grazing on the cf.Lyngbyasp. used in the feeding assays and found both to be sequestered. This study is the first example whereby compounds with significant activity against tropical parasites have been found in both the sea hareS. rickettsiand its cyanobacterial food source. These results suggest that chemical ecological studies involving sea hares and cyanobacteria continue to provide a diverse source of bioactive compounds with biotechnological potential.