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Deep-sea hydrotherrnal ecosystems are considered as the hotspots of microbial diversity on the seafloor.An amazingly rich diversity of bacteria and archaea has been described from deep-sea hydrothermal vent ecosystems,while investigation on fungi has been overlooked.In the present study,the composition and abundance of fungal community in a hydrothermal vent site at the Mid-Atlantic Ridge of the South Atlantic Ocean were investigated based on culture-dependent and-independent methods.A total of 145 fungal strains were isolated from 5 rock samples of the hydrothermal vent sites.These fungi are affiliated to 14 genera,in which Penicillium is the dominant genus.Two new fungal species were obtained,which showed low ITS sequence similarities(about 90%sequence similarity)with known fungal strains from the genera of Acremonium and Graphostroma,respectively.In addition,a total of 1,129 intemal transcribed spacer(ITS)regions of fungal rRNA gene clones were recovered from 5 hydrothermal vent rock samples using three different fungal ITS primer sets.24,31,and 10 different operational taxonomic units(OTUs)were identified from fungal-universal,Aseomycota-,and Basidiomycota-specific clone libraries,respectively.The multiple primer approach totally identified 28 phylotypes showing low similarities(≤ 97%)with available fungal sequences in the GenBank,in which 9 phylotypes showed less than 90%of sequence similarity with the reference sequences.Our results also recovered high fungal LSU rRNA gene copy numbers(5.88×105 to 6.77×106 copies/g wet rock)in the hydrothermal vent samples,suggesting that the fungi might be involved in important ecological functions in the hydrothermal vent ecosystems.