New insights into the microbiome of the deep-sea sponge Inflatella pellicula and the secondary metabolic potential of metagenome-assembled genomes and the wider microbiome

Marine sponges are found in all of the world's oceans, from the surface waters to the deepest abyssal zones. The marine sponge holobiont is a rich source of microbial and chemical diversity. Up to 63 bacterial phyla have been observed to be associated with sponges, and thousands of unique natural products have been extracted from sponges or their microbial symbionts. However, sponges from the deep sea and their associated microbial communities are relatively understudied, largely due to sampling-associated difficulties. Secondary metabolism biosynthetic gene clusters are phylogenetically distinct and hold the potential to produce novel chemistry with potential pharmacological or industrial utility. In order to gain further insights into the microbiome of the deep-sea sponge <i>Inflatella pellicula</i>, the metagenome of this sponge, sampled from a depth of 2,900 m, was sequenced. A large fraction of the sequence reads appeared to be 'biological dark matter' and could not be taxonomically classified. Further, unlike similar studies from different marine ecosystems, relatively few metagenome-assembled genomes (MAGs) could be assembled, and relatively few secondary metabolism biosynthetic gene clusters were identified. The identified clusters were, however, very dissimilar to known characterized clusters, but some shared similarities with clusters annotated in MAGs assembled from sponge metagenomes from disparate geographic locations. Therefore, renewed efforts to cultivate the hosts of these gene clusters may yield valuable small-molecule natural products.