An Anaerobic World in Sponges

Abstract

Associated microorganisms have been described in numerous marine sponges. Their metabolic activity, however, has not yet been investigated in situ. We quantified for the first time microbial processes in a living sponge. Sulfate reduction rates of up to 1200 nmol cm⁻³d⁻¹ were measured in the cold-water bacteriosponge Geodia barretti . Oxygen profiles and chemical analysis of sponge tissue and canal water revealed steep oxygen gradients and a rapid turnover of oxygen and sulfide, dependent on the pumping activity of the sponge. Identification of the microbial community with fluorescently labelled oligonucleotide probes (FISH) indicates the presence of sulfate-reducing bacteria belonging to the Desulfoarculus/Desulfomonile/Syntrophus -cluster in the choanosome of this sponge. Analysis of lipid biomarkers indicates biomass transfer from associated sulfate-reducing bacteria or other anaerobic microbes to sponge cells. These results show the presence of an anoxic micro-ecosystem in the sponge G. barretti, and imply mutualistic interactions between sponge cells and anaerobic microbes. Understanding the importance of anaerobic processes within the sponge/microbe system may help to answer unsolved questions in sponge ecology and biotechnology.

Keywords:

• Geodia barretti
• microelectrodes
• oxygen profiles
• Porifera
• sponge associated microbes
• sulfate reduction rates
• SRR
• symbiosis

Acknowledgments

We thank the crews of R/V “Hans Brattstrøm” and the Marine Biological Station of Bergen University. Access to these two installations has been supported by the IHP (Improving Human Research Potential) program of the European Union through Contract No. HPRI-CT-1999-00056. This paper represents publication no. 37 of the research program BOSMAN (03F0358 C). Financial support was provided by the Bundesministerium für Bildung und Forschung (BMBF), Germany. We thank Ines Kaesler for counting total bacterial numbers, Wolfgang Dröse for preparation of histological sponge sections, and Tobias Zöller, Susanne Sölter, Sven Possner, Martin Blumenberg, Karsten Fehler, Michael Holzwarth, and Inge Gräber for assistance and company during field work.