Cultivation-Independent Analysis of the Bacterial Community Associated With the Calcareous Sponge and Isolation of Gen. Nov., Sp. Nov., Belonging to the Barely Studied Class in the Phylum .

Marine ecosystems serve as global carbon sinks and nutrient source or breeding ground for aquatic animals. Sponges are ancient parts of these important ecosystems and can be found in caves, the deep-sea, clear waters, or more turbid environments. Here, we studied the bacterial community composition of the calcareous sponge sampled close to the island Corsica in the Mediterranean Sea with an emphasis on planctomycetes. We show that the phylum accounts for 9% of the -associated bacterial community, a 5-fold enrichment compared to the surrounding seawater. Indeed, the use of as a yet untapped source of novel planctomycetal strains led to the isolation of strain KS4. The strain represents a novel genus and species within the class in the phylum and displays interesting cell biological features, such as formation of outer membrane vesicles and an unexpected mode of cell division.