Can sponges differentiate between microbial friend or foe?

The recognition that all higher organisms live in symbiotic association with microorganisms has opened new perspectives in biology. Marine sponges (phylum Porifera) are prominent examples of such host-microbe interactions, because many species harbour enormously dense and diverse symbiotic microbial consortia within their mesohyl matrix. Their characteristic, filter-feeding lifestyle poses the need for sponges to distinguish between three categories of bacteria: food to digest, symbionts to incorporate, and pathogens to eliminate. If and how sponges discriminate between these categories is still largely unknown. This presentation will focus on recent functional insights into sponge-microbe cross talk and it will report on our efforts to move sponges from an exploratory science to one where sponges are used as experimental models for marine host-microbe symbioses.