Sponges (phylum Porifera) are basal metazoans originated more than 800 million years ago. One of its remarkable characteristics is the presence of several associated microorganisms. This association is fundamental for the survival of the holobiont, and the presence of an immune system, similar to those in higher organisms, indicates how intimately bound they are, not only physiologically, but also evolutionarily. An important event on this association must have occurred when sponges from marine origins and their associated microbiota began to occupy freshwater environments. However, there are no studies on how this process occurred. Thus, this project aims to investigate the relationships between bacteria present in freshwater sponges and their marine ancestral stock, analyzing the composition of the sponge associated bacteriome from both locations, along with the role of possible immunomodulators on the stability of this relationship and in what ways the host-microbiome complex has been modified during the process of colonization of continental water bodies.