The emergence of antibiotic resistance and viruses with high epidemic potential made unexplored marine environments an appealing target source for new metabolites. Marine fungi represent one of the most suitable sources for the discovery of new compounds. Thus, the aim of this work was (i) to isolate and identify fungi associated with the Atlantic sponge Grantia compressa; (ii) to study the fungal metabolites by applying the OSMAC approach (one strain; many compounds); (iii) to test fungal compounds for their antimicrobial activities. Twenty-one fungal strains (17 taxa) were isolated from G. compressa. The OSMAC approach revealed an astonishing metabolic diversity in the marine fungus Eurotium chevalieri MUT 2316, from which 10 compounds were extracted, isolated, and characterized. All metabolites were tested against viruses and bacteria (reference and multidrug-resistant strains). Dihydroauroglaucin completely inhibited the replication of influenza A virus; as for herpes simplex virus 1, total inhibition of replication was observed for both physcion and neoechinulin D. Six out of 10 compounds were active against Gram-positive bacteria with isodihydroauroglaucin being the most promising compound (minimal inhibitory concentration (MIC) 4–64 µg/mL) with bactericidal activity. Overall, G. compressa proved to be an outstanding source of fungal diversity. Marine fungi were capable of producing different metabolites; in particular, the compounds isolated from E. chevalieri showed promising bioactivity against well-known and emerging pathogens.

Algae-inhabiting marine fungi represent a taxonomically and ecologically interesting group of microorganisms still largely neglected, especially in temperate regions. The aim of this study was to isolate and to identify the culturable mycobiota associated with Flabellia petiolata, a green alga frequently retrieved in the Mediterranean basin. Twenty algal thalli were collected from two different sampling sites in the Mediterranean Sea (Elba Island, Italy). A polyphasic approach showed the presence of a relevant alga-associated mycobiota with 64 taxa identified. The fungal isolates belonged mainly to Ascomycota (61 taxa), while only three Basidiomycota were detected. The phylogenetic position of sterile mycelia and cryptic taxa, inferred on the basis of LSU partial region, highlighted the presence of putative new phylogenetic lineages within Dothideomycetes and Sordariomycetes. This work represents the first quali-quantitative analysis of the culturable mycobiota associated to a green alga in the Mediterranean Sea.

Summary: Fungi populate deep Oceans in extreme habitats characterized by high hydrostatic pressure, low temperature and absence of sunlight. Marine fungi are potential major contributors to biogeochemical events, critical for marine communities and food web equilibrium under climate change conditions and a valuable source of novel extremozymes and small molecules. Despite their ecophysiological and biotechnological relevance, fungal deep‐sea biodiversity has not yet been thoroughly characterized. In this study, we describe the culturable mycobiota associated with the deepest margin of the European Western Continental Shelf: sediments sampled at the Porcupine Bank and deep‐water corals and sponges sampled in the Whittard Canyon. Eighty‐seven strains were isolated, belonging to 43 taxa and mainly Ascomycota. Ten species and four genera were detected for the first time in the marine environment and a possible new species of Arachnomyces was isolated from sediments. The genera Cladosporium and Penicillium were the most frequent and detected on both substrates, followed by Candida and Emericellopsis . Our results showed two different fungal communities: sediment‐associated taxa which were predominantly saprotrophic and animal‐associated taxa which were predominantly symbiotic. This survey supports selective fungal biodiversity in the deep North Atlantic, encouraging further mycological studies on cold water coral gardens, often overexploited marine habitats.

Covering 70 % of Earth, oceans are at the same time the most common and the environment least studied by microbiologists. Considering the large gaps in our knowledge on the presence of marine fungi in the oceans, the aim of this research was to isolate and identify the culturable fungal community within three species of sponges, namely Dysidea fragilis, Pachymatisma johnstonia and Sycon ciliatum, collected in the Atlantic Ocean and never studied for their associated mycobiota. Applying different isolation methods, incubation temperatures and media, and attempting to mimic the marine and sponge environments, were fundamental to increase the number of cultivable taxa. Fungi were identified using a polyphasic approach, by means of morpho-physiological, molecular and phylogenetic techniques. The sponges revealed an astonishing fungal diversity represented by 87 fungal taxa. Each sponge hosted a specific fungal community with more than half of the associated fungi being exclusive of each invertebrate. Several species isolated and identified in this work, already known in terrestrial environment, were first reported in marine ecosystems (21 species) and in association with sponges (49 species), including the two new species Thelebolus balaustiformis and Thelebolus spongiae, demonstrating that oceans are an untapped source of biodiversity.