Microb. Ecol. 7:13-21 (1981) IYIICI BI IL ECOI.OGV Specificity of Bacterial Symbionts in Mediterranean and Great Barrier Reef Sponges* Clive R, Wilkinson, 7,, Madeleine Nowak, i Brian Austin, 2.** and Rita R. Colwell 2 1 Laboratoire d'Histologie et BiologieTissulaire,Universit6 ClaudeBernard,Villeurbanne69622, France;and 2Departmentof Microbiology,University of Maryland, CollegePark, Maryland20742, USA Abstract. Bacteria were isolated from marine sponges from the Mediterranean and the Great Barrier Reef and characterized using numerical taxonomy techniques. A similar sponge-specific bacterial symbiont was found in 9 of 10 sponges examined from both geographic regions. This symbiont occurred in sponges of two classes and seven orders, and it probably has been associated with sponges over a long geological time scale. Another symbiont apparently specific to the sponge Verongia aerophoba was found. This sponge is yellow-orange, similar in color to the bacterial symbiont. These symbionts are two of a large mixed bacterial population present in many sponges. Bacterial symbionts are common within many marine sponges. The granular material observed in the intercellular collagenous matrix (the mesohyl) of sponges was proved to be bacteria by Levi and Levi (7) using an electron microscope. Additional electron microscope studies have been made on the morphology of these bacteria and their relationship to sponge cells (13, 14, 17). The common conclusion drawn from these studies was that there 'are many morphologically different bacteria in the mesohyl of marine sponges. In two previous studies on bacteria isolated from temperate water sponges, no bacteria specific to the host sponges were detected; moreover, the bacteria isolated were similar to those in the ambient water (1, 10). These studies were limited in that the bacteria were characterized using several diagnostic tests only, and in one of the studies the bacterial populations in the sponge and particularly the ambient water were unrealistically low (10), During a study of four coral reef sponges, Wilkinson (16) isolated large numbers of bacteria from the sponges and the ambient water and characterized them by numerical taxonomy methods. In three of the sponges there was a common facultative anaerobic *This paperconstitutes No. V in the seriesMicrobialAssociationsin Sponges. **Present address: Australian Instituteof Marine Science, PMB 3, Townsville,M.S.O., Queensland, 4810, Australia. ***Presentaddress: Fish DiseasesLaboratory, Weymouth,DorsetDT4 8UB, England, 0095-3628/81/0007-0013 $01.80 1981 Springer-Vcrlag New YorkInc.