Differences between bacterial communities associated with the surface or tissue of Mediterranean sponge species

Bacterial communities associated with the surfaces of several Mediterranean sponge species (Agelas oroides, Chondrosia reniformis, Petrosia ficiformis, Geodia sp., Tethya sp., Axinella polypoides, Dysidea avara, and Oscarella lobularis) were compared to those associated with the mesohyl of sponges and other animate or inanimate reference surfaces as well as with those from bulk seawater. Denaturing gradient gel electrophoresis (DGGE) analysis of PCR-amplified bacterial 16S ribosomal RNA genes obtained from the surfaces and tissues of these sponges demonstrated that the bacterial communities were generally different from each other. The bacterial communities from sponges were different from those on reference surfaces or from bulk seawater. Additionally, clear distinctions in 16S rDNA fingerprint patterns between the bacterial communities from mesohyl samples of "high-microbial abundance (HMA) sponges" and "low-microbial abundance sponges" were revealed by DGGE and cluster analysis. A dominant occurrence of particularly GC-rich 16S ribosomal DNA (rDNA) fragments was found only in the DGGE banding pattern obtained from the mesohyl of HMA sponges. Furthermore, sequencing analysis of 16S rDNA fragments obtained from mesohyl samples of HMA sponges revealed a dominant occurrence of sponge-associated bacteria. The bacterial communities within the mesohyl of HMA sponges showed a close relationship to each other and seem to be sponge-specific.