Surface bacterial community, fatty acid profile, and antifouling activity of two congeneric sponges from Hong Kong and the Bahamas

Bacterial communities on the surfaces of 2 congeneric sponges, Mycale adhaerens from Hong Kong and M. laxissima from the Bahamas, were compared using conventional cultivation techniques and terminal restriction fragment length polymorphism (TRFLP) analysis - a culture-independent DNA fingerprinting technique. The bacterial community on the Hong Kong sponge was more diverse, in terms of the number and type of species isolated, and different from that on the Bahamas sponge, as evident from distinct clusters formed in TRFLP analysis. Distinctive bacterial types (i.e. TRFs) were commonly found on both sponge surfaces, but none of their bacterial isolates were common. At tissue level concentration, extract of the Hong Kong sponge inhibited the growth of a wide range of bacteria isolated from the Hong Kong reference surface, but did not affect any of those isolated from the Bahamas reference surface, indicating highly specific antibacterial activity. Extracts of both sponges, when incorporated into hydrogels and exposed to the natural environment for bacterial film development, dramatically altered the bacterial community in the films, either by shifting the bacterial composition or decreasing bacterial density. Settlement assays of the resulting films using larvae of the polychaete Hydroides elegans showed that the filmed hydrogels with Hong Kong sponge extracts either inhibited larval settlement or were toxic to the larvae; however, those with the Bahamas sponge extracts had no observable effect. HPLC (high performance liquid chromatography) and GC-MS (gas chromatography-mass spectrometry) analyses revealed different chemical profiles in the extracts; the Hong Kong sponge had a more diverse fatty acid profile. Our results suggest that the 2 congeneric sponges from geographically separated regions have 'species-specific', surface-associated bacterial communities and antifouling activities, which might be due to the differences in the chemical and fatty acid compositions of the 2 sponges. Alternately, different sponge-associated bacterial communities may reflect habitat differences in sympatric bacterial and fouling communities.