ABSTRACT: 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 (Vibrio parahaemolyticus), 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 concentrations). Bioassay results revealed that 16 species (48%) exhibited antibiotic activity against at least 1 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 compressa, Amphimedon erina, Aplysina lacunosa, and Ptilocaulis spiculifera inhibited the largest numbers of test strains and exhibited the most potent antibiotic activities with values frequently exceeding those of a control antibiotic (gentamicin). The pattern of antimicrobial activity was different for 15 of 16 active sponge species, suggesting that diverse taxa do not produce similar antibacterial metabolites. Overall, only 23% of the extract/bacterial interactions exhibited antibacterial activity, indicating that, in general, conspicuous members of the Caribbean sponge community do not produce broad-spectrum antibacterial metabolites. 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 Axinella corrugata (= Teichaxinella morchella) known to deter feeding by predatory reef fishes, exhibited weak antimicrobial activity, suggesting that this potent feeding deterrent is not solely responsible for the antimicrobial activity detected in the crude sponge extract.

KEY WORDS: Chemical defense · Antimicrobial · Sponges · Secondary metabolites

Published in AME Vol. 19, No. 3 (1999) on October 27
ISSN: 0948-3055. Copyright © Inter-Research, Oldendorf/Luhe, 1999