DEFENSE METABOLITES FROM THE MARINE SPONGE VERONGIA-AEROPHOBA

The marine sponge Verongia aerophoba (syn. Aplysina aerophoba) accumul ates isofistularin-3 and aerophobin-2 as major brominated isoxazoline alkaloids. Following disrupture of the compartmentation (e.g. by wound ing) both isofistularin-3 and aerophobin-2 are enzymatically converted into aeroplysinin-1 which in turn gives rise to a dienone. Aeroplysin in-1 and dienone were shown to exhibit pronounced biological activitie s in various bioassays with marine organisms (bacteria, algae and moll uscs) whereas their biogenetic precursors isofistularin-3 and aerophob in-2 were either inactive or exhibited only marginal activity. In the agar plate diffusion assay, aeroplysinin-1 and dienone were antibiotic ally active against eight different Gram-positive or Gram-negative mar ine bacteria including Alteromonas, Moraxella and Vibrio spp. Towards the marine Photobacterium phosphoreum the EC(50)s Of aeroplysinin-1 an d dienone were 3.45 and 1.37 mu M, respectively. Both compounds inhibi ted also the growth of the marine microalgae Coscinodiscus wailesii an d Prorocentrum minimum. Towards the former, the EC(50)s of aeroplysini n-1 and dienone were 5.6 and 27.9 mu M, respectively. In addition to t heir growth inhibitory activity, aeroplysinin-1 and dienone were algic idal as evident by their damaging effects on the algal cellular membra nes. The polyphagous marine gastropod Littorina littorea was repelled when exposed to either aeroplysinin-1 or dienone that were added to se awater. The EC(50) of the most active compound aeroplysinin-1 was obse rved at 0.1 mM. It is suggested that the enzymatically catalysed conve rsion of brominated metabolites in V. aerophoba represents a wound-ind uced defense mechanism hitherto unreported from the marine environment .