Antibacterial and anti-diatom activity of Hong Kong sponges

In this study, we link laboratory results with field evidence of microbial settlement responses to crude extracts of several sponge species from Hong Kong waters, including Callyspongia sp. 1, Callyspongia sp. 2, C. pulvinata, Mycale adhaerens, Haliclona cymaeformis var. 1, H. cymaeformis var. 2 and Halichondria sp. (Porifera: Demospongiae). Laboratory experiments showed that 6 out of 7 sponge extracts inhibited growth and caused mortality of the pennate diatom Nitzschia paleacea at tissue-level concentration. In disk-diffusion bioassays, extracts of the sponge Halichondria sp. inhibited the growth of 4 bacterial strains out of 11 isolated from inanimate substrata; other sponge extracts inhibited growth of only 1 or 2 bacterial strains. For field experiments, sponge metabolites were immobilized in a Phytagel® matrix and exposed to natural microbial communities. After 2 d of exposure, bacterial densities on the gels with sponge extracts were lower than on control gels. Terminal restriction fragment length polymorphism (TRFLP) analysis of PCR-amplified bacterial community 16S rRNA genes obtained from these gels demonstrated that the communities were different between the sponge extracts and control gels. After 7 d of exposure, 6 (86%) extracts suppressed the recruitment of pennate diatoms and 3 (43%) sponge extracts suppressed the recruitment of bacteria. These results suggest that sponge extracts can modify the structure of bacterial communities and decrease the density of bacteria and diatoms in microfouling communities.