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