Ascomycete phylotypes recovered from a Gulf of Mexico methane seep are identical to an uncultured deep-sea fungal clade from the Pacific

Deep-sea endemic fungi are one component of an under-sampled invisible biosphere whose contribution to benthic ecosystems is not yet understood. In the last decade, molecular techniques have facilitated the discovery of several new deep-sea fungal groups, especially in habitats such as hydrothermal vents and methane seeps. We assessed fungal diversity at a methane seep in the Gulf of Mexico by sequencing partial ITS and LSU gene regions from environmental DNA recovered from microoxic and anoxic sediment. While most phylotypes were closely allied with common fungal species, the dominant phylotype did not match any known terrestrial species and aligned with an uncultured deep-sea fungus found in oxygen-depleted sediment at multiple sites in the Pacific Ocean. Despite its apparently broad distribution and frequent occurrence in oxygen-depleted sediment, the ecological role of this phylotype is not yet known.