Abstract Description

Symbiotic relationships between marine sponges and prokaryotes have been an area of interest for several decades. As one of the oldest living eukaryotic organisms, sponges have developed intricate relationships with microbial symbionts that have allowed them to co-evolve and shape modern sponge taxa. These symbionts, often bacterial, can be either acquired either via vertical transmission from parent to progeny, or through filtration of surrounding seawater. These symbionts can be maintained in the sponge host due to roles in nutrient uptake and cycling, waste and metabolic byproduct recycling, amino acid production, skeletal support and providing chemical defence against pathogens and predators through the production of bioactive secondary metabolites. Although the mechanisms by which the sponges distinguish between ‘food, friend and foe’ bacteria are unknown, it is likely that the composition and structure of cellular components such as lipopolysaccharides, peptidoglycans and flagella allow the host to distinguish between the three and establish symbiotic relationships. The taxonomic and functional diversity of LMA sponge-bacterial symbionts is generally host-specific and distinct from the surrounding seawater. However, there are several ubiquitous or broad-host range symbionts such as the Poribacteria, Sponge-associated unclassified lineages (SAUL) and the newly discovered Tethybacterales symbionts that associate with phylogenetically distinct hosts. Previous work shows that the Tethybacterales symbionts represent an older order of sponge symbionts in the Latrunculiidae family acquired approximately 0.6*rate million years ago. Through the characterization of metagenome-assembled genomes (MAGs) from sponge representatives of the Latrunculiidae, Irciniidae and Chaliniidae families we have established the evolutionary and functional profiles of these three symbiont lineages using comparative metagenomics.