Sponges form close relationships with bacteria, and a remarkable phylogenetic diversity of yet-uncultured bacteria has been identified from sponges using molecular methods. In this study, we use a comparative metagenomic analysis of the bacterial community in the model sponge Cymbastela concentrica and in the surrounding seawater to identify previously unrecognized genomic signatures and functions for sponge bacteria. We observed a surprisingly large number of transposable insertion elements, a feature also observed in other symbiotic bacteria, as well as a set of predicted mechanisms that may defend the sponge community against the introduction of foreign DNA and hence contribute to its genetic resilience. Moreover, several shared metabolic interactions between bacteria and host include vitamin production, nutrient transport and utilization, and redox sensing and response. Finally, an abundance of protein-protein interactions mediated through ankyrin and tetratricopeptide repeat proteins could represent a mechanism for the sponge to discriminate between food and resident bacteria. These data provide new insight into the evolution of symbiotic diversity, microbial metabolism and host-microbe interactions in sponges.

Persistence of the opportunistic bacterial pathogen Vibrio cholerae in aquatic environments is the principal cause for seasonal occurrence of cholera epidemics. This causality has been explained by postulating that V. cholerae forms biofilms in association with animate and inanimate surfaces. Alternatively, it has been proposed that bacterial pathogens are an integral part of the natural microbial food web and thus their survival is constrained by protozoan predation. Here, we report that both explanations are interrelated. Our data show that biofilms are the protective agent enabling V. cholerae to survive protozoan grazing while their planktonic counterparts are eliminated. Grazing on planktonic V. cholerae was found to select for the biofilm-enhancing rugose phase variant, which is adapted to the surface-associated niche by the production of exopolymers. Interestingly, grazing resistance in V. cholerae biofilms was not attained by exopolymer production alone but was accomplished by the secretion of an antiprotozoal factor that inhibits protozoan feeding activity. We identified that the cell density-dependent regulator hapR controls the production of this factor in biofilms. The inhibitory effect of V. cholerae biofilms was found to be widespread among toxigenic and nontoxigenic isolates. Our results provide a mechanistic explanation for the adaptive advantage of surface-associated growth in the environmental persistence of V. cholerae and suggest an important contribution of protozoan predation in the selective enrichment of biofilm-forming strains in the out-of-host environment.grazing ͉ resistance ͉ protozoa ͉ quorum sensing E pidemics of cholera, an acute intestinal infection caused by toxigenic strains of the facultative pathogen Vibrio cholerae, are a major public health problem in developing countries around the globe. Both toxigenic and nontoxigenic strains of V. cholerae are natural inhabitants of a wide range of aquatic ecosystems, including estuarine and coastal waters, that provide the environmental reservoir of virulent V. cholerae strains (1). The fact that many environmental nontoxigenic strains carry virulence genes (2, 3) and that the occurrence of epidemics coincides with the increased prevalence of the causative V. cholerae strain in the aquatic environment (4, 5) supports the notion of an environmental origin of toxigenic V. cholerae clones. This view has led to the hypothesis that cholera epidemics are triggered by environmental factors and selective forces governing aquatic microbial communities. In recent years, studies on the ecology of V. cholerae have considerably increased our understanding of physical and biological parameters that influence the persistence of V. cholerae in the environment and hold the potential to predict the outbreak of cholera epidemics (6).As a member of the natural bacterioplankton community, V. cholerae is an integral part of the pelagic microbial food web and is thus constrained in its growth and survival by the predatory action of bacterivorous protists, so...

The functional metagenomic screening of the microbial communities associated with a temperate marine sponge and a green alga identified three novel hydrolytic enzymes with antibacterial activities. The results suggest that uncultured alpha-and gammaproteobacteria contain new classes of proteins that may be a source of antibacterial agents.