Antimicrobial activity of Caribbean sponge extracts

Marine sponges produce a diversity of unusual chemical compounds, but the ecological functions of these metabolites remain largely unknown. To determine if sponge secondary metabolites have ecologically significant antimicrobial effects, organic extracts from 33 species of Caribbean sponges were assayed for antibiotic activity against a test panel of marine bacteria. The test panel consisted of 8 strains representing 6 genera of marine bacteria and included an opportunistic pathogen ( Vibnoparahaemolyticus), a common fouling bacterium (Deleya marina), and strains isolated from seawater and healthy and necrotic Caribbean sponges. Extracts were tested for antibiotic activity at concentrations that were volumetrically equivalent to those found in sponge tissues (whole-tissue concentratlons). Bioassay results revealed that 16 species (48%) exhibited antibiotic activity against at least l bacterial isolate and that the 2 bacteria isolated from necrotic sponge tissues were the most sensitive test strains (inhibited by 40% of the extracts). Extracts from Amphimedon cornpressa, Amphimedon erina, Aplysina lacunosa, and Ptdocaulis spicuhfera inhibited the largest numbers of test stralns and exhibited the most potent antibiotic activities with values frequently exceeding those of a control antibiotic (gentarnicin). The pattern of antimicrobial activity was different for 15 of 16 active sponge specles, suggesting that diverse taxa do not produce similar antibacterial metabohtes. Overall, only 23 % of the extract/bacterial interactions exhibited antibactenal activity, indicating that, in general, conspicuous members of the Caribbean sponge community do not produce broad-spectrum anttbacterial metabolltes. All of the species yielding antibacterial extracts also deterred feeding by reef fishes in a previous study, suggesting that some secondary metabolites may have evolved multiple defensive functions Stevensine, a compound from Axnella corrugata (= Teichaxinella morchella) known to deter feed~ng by predatory reef fishes, exhibited weak antimicrobial activity, suggesting that this potent feedlng deterrent is not solely responsible for the antimicrobial activity detected in the crude sponge extract. KEY WORDSChemical defense . Antimicrobial . Sponges . Secondary metabolites