Monitoring microbial community composition by fluorescence in situ hybridization during cultivation of the marine cold-water sponge Geodia barretti.

To determine the stability and specificity of microbes associated with the marine cold-water sponge Geodia barretti during cultivation, we compared the microbial community of freshly retrieved specimens to that of cultivated explants by fluorescence in situ hybridization (FISH). G. barretti hosts a specific homogeneous microbial community in its mesohyl, which is maintained during a cultivation period of 8 months. In 10-day-old explants, bright colonies of unusually large bacterial cells, located predominantly at canal walls, were observed in addition to the common bacteria. Bacteria of the aberrant type included both lineages present in whole sponges and foreign ones, notably numerous genera of sulfate-reducing bacteria. We assume that these represent infectious bacteria that eluded the innate immune system of the sponge. Explants that resist these microbial attacks during the critical phase of cultivation eliminate infectious bacteria. The intrinsic microbial community of G. barretti is not affected by these infections and remains persistent over a cultivation period of at least several months.