Marine Mycobiomes Colonize Mediterranean Sponge Hosts in a Random Fashion

Marine sponges are widespread, sessile, filter-feeding animals, known for living in association with complex prokaryotic communities structured by host species. Though marine fungi are ubiquitous across marine environments, little is known about sponge-associated fungal communities (mycobiome). Indeed, aside from a few studies based on the isolation of fungal strains for biotechnological purposes, little information is available to understand the diversity and structure of sponge mycobiome. Here, a metabarcoding approach based on the ITS1 marker was applied to examine the structure and composition of fungal communities associated with four Mediterranean sponges. The species: Petrosia ficiformis, Chondrosia reniformis, Crambe crambe, and Chondrilla nucula were analyzed along with the surrounding seawater, revealing Aspergillus (1-56%), Cladosporium (1-75%), Malassezia (1-38.5%), and Pennicillium (1.5-36%) as the most represented fungal genera. Our data showed high intra-specific variability and no clear core mycobiome within each of the sponge species host, suggesting stochastic and perhaps transient community membership. This study sheds light on one of the most abundant yet least understood components of the marine ecosystem. Unraveling the dynamics of fungal interactions within sponge holobionts is essential to advance our understanding of their ecological roles and functions. By addressing the enigmatic nature of sponge-associated fungi, this research opens new avenues for exploring their contributions to marine ecosystems and resolving the many unanswered questions in this field.