Antifouling activity and microbial diversity of two congeneric sponges Callyspongia spp. from Hong Kong and the Bahamas

Microbial communities of the sponges Callyspongia sp. from Hong Kong and Callyspongia plicifera (Porifera: Demospongia) from the Bahamas were compared with each other and with those from reference substrata using a terminal restriction fragment length polymorphism (T-RFLP) analysis. The least number of bacterial ribotypes and bacterial isolates were retrieved from Bahamas reference and sponge surfaces, while the bacterial communities from Hong Kong Callyspongia sp. and reference surfaces were more diverse. Microbial communities from the 2 sponges were different from each other and from reference substrata. Gas chromatographic-mass spectrometric (GC-MS) analysis of dichloromethane extracts revealed that more than 60% of the compounds were similar in the 2 species Callyspongia sp. and C, plicifera, compared to the compounds of Halichondria spp. At tissue level (TL) concentrations, both sponge extracts predominantly inhibited the growth of bacteria from reference substrata. Multifactor ANOVA revealed that the source of bacteria (sponge surface, interior, or reference substrata), the geographic location of isolates (Hong Kong or the Bahamas), the sponge extract (from Callyspongia sp. or from C. plicifera), and combinations of these factors contributed significant effects in disc diffusion assay experiments. Sponge extracts at both TL concentrations and 10x dilutions were toxic to larvae of the polychaete Hydroides elegans and the barnacle Balanus amphitrite. Our results suggest that the 2 congeneric sponges Callyspongia spp. from different biogeographic regions have different bacterial associates, while producing relatively similar secondary metabolites. It remains to be explored whether differences in sponge-associated bacterial communities will also hold for other congeneric sponge species from different regions.