Abstract
Deep-sea sediments are vast microbial habitats that cover almost two-thirds of the planet’s surface. Particularly, sediments in hydrothermal vents and oxygen minimum zones (OMZ) represent emblematic, and poorly understood extreme niches that pose strong selective pressures to life, representing untapped reservoirs of a unique microbial diversity. Nonetheless, the mycobiota in these systems remains relatively unknown. Here, we explored fungal diversity and community structure in deep-sea sediments collected from low- and high-temperature vent systems (Pescadero Basin, Pescadero Transform Fault, and Alarcón Rise) and an OMZ (Alfonso Basin) in the southern Gulf of California, by using high-throughput Illumina sequencing of the ITS1 region. We identified 102 fungal amplicon sequence variants (ASVs), principally affiliated to the Ascomycota and Basidiomycota. Our results also evidenced a high proportion of widely distributed, uncultured phylotypes (e.g., unknown clades closely related to the Basidiomycota such asFungisp. 18 and 19 formerly reported from deep-sea), evidencing the copious occurrence of novel fungal lineages with limited distribution to deep-sea sediments. Overall, the largest number of ASVs was recovered from high-temperature vent systems, corroborating these as diversity hotspots. In addition, clustering patterns across samples and the FUNGuild analysis revealed characteristic assemblages in each ecosystem, which could be linked to site-specific processes. This study provides baseline data paving the way for a better understanding of deep-sea fungal diversity, evidencing its potential importance in ecosystem functioning.
Highlights
Deep-sea seafloor covers around 95% of Earth’s surface, representing the largest biome (Danovaro et al, 2014, 2017)
We report the first ITS rRNA survey of fungal diversity in deep-sea sediments collected in Pescadero Basin (PB), Pescadero Transform Fault (PTF), Alarcón Rise (AR), and Alfonso Basin (AB), in the southern Gulf of California, Mexico
Overall we obtained 184,466 reads from the analyzed sediment samples collected in high-temperature hydrothermal vent fields in the Pescadero Basin (47,917 reads) and the Alarcón Rise (32,941 reads), low-temperature hydrothermal vent fields in the Pescadero Transform Fault (61,106 reads), and oxygen minimum zones (OMZ) in Alfonso Basin (42,502 reads) (Supplementary Table 1)
Summary
Deep-sea seafloor (below 200 m depth) covers around 95% of Earth’s surface, representing the largest biome (Danovaro et al, 2014, 2017). Hydrothermal vents are extreme environments where fluids that are geothermally heated and enriched in reduced compounds and trace metals exit to the seafloor reaching temperatures from 330 to 400◦C (Van Dover, 2014) They host complex biological communities where primary production is fundamentally driven by sulfur-based chemosynthesis, as fluids provide free-living and endosymbiotic bacteria with chemical energy. OMZ are steady-state low-oxygen layers at mid-water depths (Diaz et al, 2013) that are widespread in the northeast subarctic Pacific, the northern Indian Ocean, and the Eastern Tropical Pacific (Paulmier and Ruiz-Pino, 2009) They are formed in areas of high primary production in the surface waters and poor circulation, where the biological degradation of the sinking organic matter results in oxygen depletion (Rogers, 2000; Levin, 2003). About 1,150,000 km of the seafloor is exposed to oxygen concentrations
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