Marine sponges acquire nutrients by filtering and eating bacteria from the seawater, but they also at the same time harbour a remarkable diversity of bacterial symbionts that don’t get digested. We are characterising this sponge symbiont diversity on a global scale as part of the Earth Microbiome Project and with a large network of collaborators. Using high-throughput sequencing we have gained insight into the microbial diversity of 1000s of sponge samples and have defined evolutionary and ecological features that determine the structure and composition of symbiont communities. We have also recently discovered that the genomes of bacterial sponge symbionts carry a large number of proteins that are similar to eukaryotic proteins controlling phagocytosis and cytoskeletal formation (Fan et al. PNAS USA 2012, Nguyen et al. Molecular Ecology 2013). We hypothesise that symbionts use these protein to “manipulate” the sponge and currently analyse this with a range of phylogenetic, -omics based and molecular-biological approaches. The outcome of this project will provide important information on the evolution of microbe-host interactions. The work is supported by the Gordon and Betty Moore Foundation and research data can be found in the following link: https://cloudstor.aarnet.edu.au/plus/index.php/s/d3288d00b22fef86bd3e8988042e9ca2. For more information contact A/ Prof Torsten Thomas.