Antibacterial activity of the sponge Ircinia ramosa: Importance of its surface-associated bacteria

Variations in the antibacterial activity of the sponge Ircinia ramosa were evaluated during two collection periods (January and May) against vicinity fouling bacteria (VFB) and sponge surface-associated bacteria (SAB). The de nsity of fouling bacteria in the water column, as well as epibacterial abun dance on the sponge surface, was enumerated during both collections, and bo th increased in the warmer month of May. The extracts obtained from SAB wer e also tested for their role in antibacterial activity of the host. Sponge- associated bacteria are capable of producing antibacterial metabolites. The antibacterial activity that originated from polar fractions in the cooler month of January shifted towards the nonpolar fractions in May. Nonpolar fr actions were more useful for the sponge when threatened with increased bact erial density. Thus, the chemical nature and production of antibacterial co mpounds produced by sponge or its associated bacteria appears to be governe d by the environment. An inverse relationship was observed between the epib acterial abundance over the sponge surface in nature and the antibacterial activity displayed by the sponge extracts in laboratory bioassays. This inv estigation reveals the importance of collection period as well as the role of associated bacteria in the evaluation of antibacterial activity.