EVIDENCE FOR A SYMBIOSIS BETWEEN BACTERIA OF THE GENUS RHODOBACTER AND THE MARINE SPONGE HALICHONDRIA-PANICEA - HARBOR ALSO FOR PUTATIVELY TOXIC BACTERIA

Halichondria panicea (Pallas) is a marine sponge, abundantly occurring in the Adriatic Sea, North Sea, and Baltic Sea. It was the aim of the present study to investigate if this sponge species harbors bacteria. Cross sections through H. panicea were taken and inspected by electro n microscopy. The micrographs showed that this sponge species is colon ized by bacteria in its mesohyl compartment. To identify the bacteria, polymerase chain reaction (PCR) analysis of the 16S rRNA gene segment , typical for bacteria, was performed. DNA was isolated from sponge ma terial that had been collected near Rovinj (Adriatic Sea), Helgoland ( North Sea), and Kiel (Baltic Sea) and was amplified with bacterial pri mers by PCR. The data gathered indicate that in all samples bacteria b elonging to the genus Rhodobacter (Proteobacteria, subdivision alpha) are dominant, suggesting that these bacteria live in symbiotic relatio nship with the sponge. In addition, the results show that the differen t samples taken contain further bacterial species, some of them belong ing to the same genus even though found in sponges from different loca tions. The possibility of the presence of toxic bacteria was supported by the finding that organic extracts prepared from sponge samples dis played toxicity, when analyzed in vitro using leukemia cells.