Antifouling properties of 10β-formamidokalihinol-A and kalihinol A isolated from the marine sponge Acanthella cavernosa

Abstract

Many soft-bodied sessile marine invertebrates such as sponges and soft corals defend themselves against fouling directly through the production of antifouling compounds, or indirectly through regulating the epibiotic microbes that affect larval settlement. In this study, 10β-formamidokalihinol-A and kalihinol A were isolated and purified from the marine sponge Acanthella cavernosa (Dendy). The results indicated that both compounds inhibited the growth of bacteria isolated from the natural environment whereas kalihinol A suppressed larval settlement of a major fouling polychaete, Hydroides elegans with an EC₅₀ of 0.5 μg ml⁻¹. Kalihinol A was incorporated in Phytagel® that was exposed to the bacterial consortia in natural seawater for biofilm formation. Biofilms that developed on the Phytagel® surfaces were analysed for bacterial abundance and bacterial species composition using a DNA fingerprinting technique, terminal restriction fragment length polymorphism (T-RFLP). The results showed that kalihinol A only slightly reduced bacterial abundance (t-test, p = 0.0497), but modified the bacterial species composition of the biofilms. Inhibition of H. elegans larval settlement was observed when biofilms developed under the influence of kalihinol A were exposed to larvae, suggesting that compounds like kalihinol A from the sponge A. cavernosa may change bacterial community composition on the sponge surface, which in turn, modulates larval settlement of fouling organisms.

Keywords:

• Bacterial abundance
• bacterial diversity
• T-RFLP
• larval settlement
• sponge
• antifoulants

Acknowledgements

We would like to thank Professor Tadeusz F. Molinski from the Department of Chemistry at the University of California at Davis and Dr William F. Reynolds from the Department of Chemistry at the University of Toronto for their help in verifying the identity of the compounds, Mr J. H. Tang from the Sanya Joint Laboratory of Marine Sciences for his assistance in specimen collection, and Professor J. H. Li of the Institute of Oceanology, Chinese Academy of Sciences for identifying the sponges. We thank Ms Y. K. Tam and Ms M. Y. Tsoi (HKUST) for assistance in community fingerprint analysis, Drs T. Harder, S. Dobretsov and H.-U. Dahms (HKUST) for useful comments, and Dr V. Unkefer for proofreading the manuscript. This work was supported by grants (CAG04/05.SC01) from the Research Grants Council of the Hong Kong SAR Government and a Croucher Foundation Fund grant (CAS-CF03/04.SC01) to P. Y. Qian.