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Abstract

The chemodiversity and cultivable bacterial diversity of temperate calcareous sponges were investigated in a time series of collection of two sponges, Leuconia johnstoni (Baerida, Calcaronea) collected from the northeastern Atlantic Ocean and Clathrina clathrus (Clathrinida, Calcinea) collected from the northwestern Mediterranean Sea, using combined chemical and microbiological approaches. Bacteria were visualized in tissue sections of these sponges with Gram staining and in situ hybridization. The sponge crude extracts revealed annually persistent biological activities against reference human pathogen strains: L. johnstoni extracts displayed antimicrobial activity against a Gram positive Staphylococcus aureus strain; C. clathrus extracts displayed a broad spectrum of antimicrobial activities against Gram positive S. aureus and Gram negative Escherichia coli strains as well as against the yeast Candida albicans. In order to determine the sponge or bacterial origin of the secondary metabolites isolated from the sponge holobiont, sponge cells and bacteria were separated via differential centrifugation of dissociated sponge suspensions and each fraction was screened for biological activity. The aerobic cultivable bacteria associated with these calcareous sponges were isolated, amounting to about 105 − 5 × 106 bacteria per sponge wet weight. Based on 16S rRNA sequence comparison, the bacterial community was found in both species to be composed mostly of Gammaproteobacteria (60-80%) and Alpha-proteobacteria (15%), with a few Firmicutes, Actinobacteria and Bacteroidetes. A range of biologically active compounds were purified from crude extracts of sponge or from culture broths of bacterial isolates. Ecological implications for the host sponge are being discussed based on localization and abundance of the producing bacteria in situ in the sponge tissue and on the co-detection of the chemical fingerprint of the bacterial metabolites in the host extracts. Some bacterial compounds were shown to have a role as chemical mediators of interactions within the sponge-associated bacterial compartment.

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