Onygenales from marine sediments: diversity, novel taxa, global distribution, and adaptability to the marine environment

The Onygenales represent a versatile group of fungi that primarily inhabit soils, degrading cellulose and / or keratin. While some are known human pathogens, others are osmotolerant or colonize chitin substrates such as insects. The marine environment, characterized by 3.5 % salinity and chitin as the dominant polysaccharide, represents an intriguing niche for these fungi.

However, fungal diversity in this environment remains poorly studied. This study investigated the culturable diversity of Onygenales in marine sediments, explored their global biogeography, and assessed their adaptability to marine conditions. Marine sediments were collected near river mouths and other coastal areas along the Catalan coast (Spain).

Identification was based on a polyphasic approach; global distribution patterns were assessed through the GlobalFungi database, and adaptability was evaluated through osmotolerance and substrate degradation assays (cellulose, chitin, keratin). We recovered 32 strains, of which 24 represented 16 known species distributed in Gymnascella, Gymnoascus, Narasimhella, and Sporendonema (Gymnoascaceae); Malbranchea (Malbrancheaceae); Myriodontium (Neoarthropsidaceae); and Aphanoascus and Byssoonygena (Onygenaceae).

The remaining eight strains were delineated as six novel species, including a new genus: Gymnoascoideus alboluteus sp. nov., Malbranchea parafilamentosa sp. nov., M. sedimenticola sp. nov., M. seminuda sp. nov., M. sexualis sp. nov., and Deilomyces minimus gen. et sp. nov. In addition, all strains degraded cellulose, and most tolerated up to 10 % NaCl. Only four species that also degraded chitin (Malbranchea parafilamentosa, M. sexualis, Myriodontium keratinophilum, and Sporendonema casei) could be considered facultative marine fungi.

This work evidences the great diversity of onygenalean fungi in marine sediments and underscores their metabolic adaptability to marine conditions.