Effects of Caribbean sponge extracts on bacterial attachment

Attachment is one of the first steps in bacterial colonization. By inhibiting bacterial attachment on surface cells, sponges may not only prevent infection, but also the process of biofouling. Crude organic extracts from 26 species of Caribbean sponges were assayed for their ability to inhibit bacterial attachment. Bacterial attachment was tested using Vibrio harveyi, a motile marine bacterium, isolated from seawater collected above one of the reefs from which sponges were sampled. Extracts were incorporated into agar blocks at concentrations volumetrically equivalent to whole sponge tissue. Extracts from 21 of 26 species (81%) resulted in bacterial attachment on treated blocks that was <40% of attachment on controls. Of these extracts, 9 were particularly active, with mean levels of attachment <8% of controls (Agelas conifera, Ailochroia crassa, Aka coralliphagum, Amphimedon compressa, Aplysina fulva, Erylus formosus, Plakortis halichondroides, Ptilocaulis spiculifera, Verongula gigantea). Extracts from 4 species (Ailochroia crassa, Chondrilla nucula, Ectyoplasia ferox, and Iotrochota birotulata) inhibited bacterial attachment in this assay but were not found to inhibit bacterial growth in a previous study. Purified compounds that deterred feeding of predatory fishes in a prior study were also tested for their effects on bacterial attachment; they were: oroidin, 4,5-dibromopyrrole-2-carboxylic acid and sceptrin from Agelas species, amphitoxin from A. compressa, aeroplysinin-1 and dibromocyclohexadienone from Aplysina species, steroidal glycosides from E. ferox, and formoside from E. formosus. Of these, all but the steroidal glycosides from E. ferox deterred bacterial attachment at natural concentrations, providing evidence that sponge secondary metabolites may have multiple ecological functions.