This study reports the discovery of two eukaryotic Nucleocytoviricota genomes from subsurface oceanic crustal fluids. Both genomes possess a tRNA Tyr gene with an intron, a feature common in eukaryotic and archaeal tRNA genes, and fungal genes acquired through horizontal gene transfer (HGT). The dominance of Ascomycota fungi in crustal fluids and the evidence for HGT suggest these fungi as the putative hosts, representing the first putative fungi-Nucleocytoviricota association. The findings suggest active host-viral dynamics within this ecosystem and raise questions about the impact of viral infection on productivity and biogeochemical cycling.

Ananda S. Bhattacharjee, Frederik Schulz, Tanja Woyke, Beth N. Orcutt, Joaquín Martínez Martínez