Monitoring microbial diversity and natural product profiles of the sponge Aplysina cavernicola following transplantation Received: 4 June 2002 / Accepted: 25 November 2002 / Published online: 4 February 2003 Ó Springer-Verlag 2003 Abstract In order to assess the stability of the microbial community of the sponge Aplysina cavernicola under in situ conditions, sponges were transplanted from their original location (>40 m depth) to shallower, more light-exposed sites (7–15 m depth). Transmission elec- tron microscopy revealed that the microbial community remained visually unchanged and free of cyanobacteria over the experimental time period of 3 months. Dena- turing gradient gel electrophoresis (DGGE) of PCR- amplified partial 16S rRNA gene sequences allowed a distinction between the variable and permanent fraction of the bacterial community. Comparative sequence analysis of four variable DGGE bands revealed high sequence similarity to representatives of the Alpha- and Gammaproteobacteria and the phylum Bacteroidetes, which have been recovered previously from Mediterra- nean seawater as clone sequences or by cultivation. Seven (out of 12) permanent DGGE bands showed high sequence similarity to a sponge-specific, monophyletic 16S rRNA gene sequence cluster within the Acidobac- teria division, and to a sequence cluster of uncertain affiliation. These sequence clusters represent members of a common microbial community that is shared among distantly related sponges from different, non-overlap- ping geographic regions. Four additional permanent DGGE bands showed high sequence similarity to a Betaproteobacterium, Burkholderia cepacia, which is not typically known as a marine bacterium. High-perfor- mance liquid chromatography analyses of sponge tissues revealed no changes in metabolite pattern, indicating that these compounds are expressed constitutively irre- spective of the variations resulting from the transplan- tation experiment. Introduction Microorganisms play an important role in the diet of sponges (Porifera). As filter feeders, they pump large volumes of seawater (up to 24 m 3 kg )1 sponge day )1 ) through a specialized canal system that permeates the sponge body (Vogel 1977). Microorganisms are filtered out in the choanocyte chambers and transferred into the sponge matrix, termed the mesohyl. The filtration capacities of sponges are remarkable considering that typical seawater contains 1–5·10 6 bacteria ml )1 and that the expelled seawater is essentially sterile (Reiswig 1974; Pile 1997; Wehrl 2001). Once inside the mesohyl matrix, microorganisms are physically separated from the sur- rounding seawater by contiguous host membranes. Bacteria are digested via phagocytosis by amoeboid sponge cells, termed archaeocytes (van Soest 1996). There is, however, compelling evidence that a large fraction of mesohyl-associated bacteria may be resistant to digestion. Electron microscopical observations reveal that the abundant bacterial morphotypes in sponges contain slime capsules, enlarged periplasms and addi- tional membranes, which probably serve as shields and barriers to prevent digestion (Wilkinson et al. 1981; Friedrich et al. 1999). The occurrence of large amounts of bacteria is typical for some demosponges (Vacelet and Donadey 1977; Wilkinson 1987; Willenz and Hartman 1989). In fact, sponges often profit from bacteria-specific traits, such as autotrophy, nitrogen fixation and nitrification Marine Biology (2003) 142: 685–692 DOI 10.1007/s00227-002-1000-9 C. Thoms Æ M. Horn Æ M. Wagner Æ U. Hentschel P. Proksch Communicated by O. Kinne, Oldendorf/Luhe C. Thoms Æ P. Proksch Institut fu¨r Pharmazeutische Biologie, Universita¨t Du¨sseldorf, Universita¨ tsstrasse 1, Geb. 26.23, 40225 Du¨sseldorf, Germany M. Horn Æ M. Wagner Lehrstuhl fu¨r Mikrobiologie, Technische Universita¨t Mu¨nchen, Am Hochanger 4, 85350 Freising, Germany U. Hentschel (&) Institut fu¨r Molekulare Infektionsbiologie, Universita¨t Wu¨rzburg, Ro¨ntgenring 11, 97070 Wu¨rzburg, Germany E-mail: ute.hentschel@mail.uni-wuerzburg.de Tel.: +49-931-312588 Fax: +49-931-312578