A Review on Deep-sea Fungi: Occurrence, Diversity and Adaptations

The few studies that have been carried out on deep-sea fungi in recent years either by culturing or molecular signatures, have provided evidence about their presence. A majority of culture-dependent and culture-independent fungi recovered showed homology to species reported in the terrestrial environment indicating their possible arrival in deep sea either with wind or terrestrial runoffs. However, presence of novel fungal sequences with less than 97 % similarity to previously identified fungal sequences in public databases has also been reported. Several filamentous fungi and yeasts recovered from deep-sea sediments of the Central Indian Basin from a depth of ~5000 m showed growth under hydrostatic pressures of 20-40 MPa and 5C. Some of these fungi showed unusual morphology during the initial culturing and also when grown at 20 MPa/5C. Direct detection of fungal hyphae in deep-sea sediments is a daunting task as they are present in low abundance. We demonstrated the presence of fungal hyphae in deep-sea sediments by direct staining of the sediments with Calcofluor, a fluorescent optical brightener. This review presents data on the occurrence, diversity and adaptations of fungi to various deep-sea habitats, with a special emphasis on their possible ecological role under these extreme environmental conditions.