AME 43:55-65 (2006)  -  doi:10.3354/ame043055

ABSTRACT: It has long been hypothesized that sponges can produce bioactive compounds to modulate bacterial communities on their body surfaces and that the modulated bacterial communities can protect the sponge host from being colonized by other invertebrates. Conventionally, testing of this hypothesis has relied on bioassays involving bacteria isolated from ecologically relevant sites. However, this approach generally suffers from the fact that only <1% of the total bacterial population in the natural environment is culturable using existing techniques. In this study, a bacterial culture-independent method was employed to investigate if the metabolites of the sponge Mycale adhaerens could render surface-colonizing bacterial communities inhibitive to larval settlement of Hydroides elegans, a polychaete worm that co-exists with M. adhaerens in Hong Kong waters. Organic extracts of the sponge tissue were immobilized in hydrogels and then exposed to a continuous flow of natural seawater for the development of microbial films. Epifluorescence microscopy and DNA fingerprinting analysis of bacterial community in the microbial films revealed that the extracts drastically altered bacterial community composition on the hydrogel surfaces. Subsequently, these microbial films demonstrated either an anti-settlement or toxic effect on the larvae of H. elegans. These results suggested that sponge extracts can potentially prevent epibiosis via the modulation of spongeassociated bacterial communities.

KEY WORDS: Mycale adhaerens · Hydroides elegans · Surface bacterial community · Bioactive compounds · Bacterial density · Culture-independent method · Hydrogels