Fungal diversity in the deep-sea hadal sediments of the Yap Trench by cultivation and high throughput sequencing methods based on ITS rRNA gene

The hadal zone is among the least studied habitats on the planet, and the composition, distribution and variations of the biological communities in the hadal zone are poorly understood. Recent explorations of the ocean trenches have revealed distinctive metabolic and functional microbial communities in the hadal biosphere. Compared to bacteria and archaea, fungal community in hadal trenches is poorly documented. In this study, we present, for the first time, results of a comparative survey of the sediment-associated fungal communities at the Yap Trench by using high-throughput sequencing and culture-based techniques. The fungal diversity obtained from these techniques were different, with 11.1% of the fungal genera shared between both techniques. Through ITS2 (internal transcribed spacer 2 of the rDNA) metabarcode sequencing from 42 sediment samples, 890 fungal operational taxonomic units (OTUs) were found based on clustering at a 97% sequence similarity cutoff level. Of these OTUs, 98 OTUs belonged to Ascomycota, 52 OTUs to Basidiomycota, 1 OTU to Chytridiomycota, 4 OTUs to Mortierellomycota, 19 OTUs to Mucoromycota and 2 OTUs to Rozellomycota, whereas 714 OTUs could not be assigned to any fungal phylum. The Ascomycota and the Basidiomycota comprised 49.74% and 5.84% of the total sequences, respectively t. Eurotiomycetes was identified as the most dominant fungal class. The culture-based technique also revealed Eurotiomycetes as the most abundant class, but some classes, such as Endogonomycetes and Umbelopsidomycetes, were not detected by the culture-based technique. Altogether, our findings provide valuable information for the understanding of fungal distribution and potential ecological roles of fungi in deep-sea hadal trenches.