The oceanic igneous crust is a vast reservoir of microbial life that remains largely unexplored. Fungi are the only eukaryotes that have been found in this ecosystem, and there is increasing evidence that they are viable and transcriptionally active. Additionally, archaeal and bacterial viruses were previously detected by metagenomics in oceanic crustal fluids. Viruses play crucial roles in ecology, evolution, and biogeochemical cycling through host infection. However, until now, the diversity and impacts of fungal viruses in this environment had not been investigated. Here we report the discovery of two eukaryotic Nucleocytoviricota genomes in crustal fluids from the Juan de Fuca Ridge by sorting and sequencing single virions. The dominance of Ascomycota fungi as the main eukaryotes in the crustal fluids, the presence of eukaryotic tRNA genes in the two viral genomes, and the evidence of fungal genes acquired through horizontal gene transfer events point to these fungi as the putative hosts, making these the first putative fungi-Nucleocytoviricota specific association. Our study suggests active fungal-viral dynamics in the subsurface oceanic crust and raises important questions about the impact of viral infection on productivity and biogeochemical cycling in this ecosystem.

Primary Presenter: Joaquin Martinez Martinez, Bigelow Laboratory for Ocean Sciences (jmartinez@bigelow.org)

Authors:

Joaquín Martinez Martinez, Bigelow Laboratory for Ocean Sciences  (jmartinez@bigelow.org)

Ananda Bhattacharjee, University of California Riverside  (anandab@ucr.edu)

Frederik Schulz, US Department of Energy Joint Genome Institute  (fschulz@lbl.gov)

Tanja Woyke, US Department of Energy Joint Genome Institute  (twoyke@lbl.gov)

Beth Orcutt, Bigelow Laboratory for Ocean Sciences  (borcutt@bigelow.org)