Marine sponges as models for commensal microbe-host interactions

In nature, multiple-species rather than single-species microbial associations with plant or animal (including human) hosts are the rule more than the exception. Prominent examples are the microbial consortia of vertebrate intestines and cattle rumen. As many demosponges are associated with enormous amounts of microorganisms, contributing up to 40-60% of the sponge biomass, they are excellent models for marine multi-species, microbe-host associations. Representatives of at least eight different phyla, many of which contain few or no cultivated representatives, have been identified as specific members of the sponge-associated microbiota. Recent studies show that vertical transmission of symbionts through the larval stages rather than horizontal acquisition from seawater appears to be an important mechanism by which the complex and possibly ancient microbial consortia of sponges are formed