Nika Pende (@nikapende.bsky.social)

Active virus-host system in a Lokiarchaeon culture Asgard archaea are considered the closest prokaryotic relatives of eukaryotes and having a crucial role in eukaryogenesis. Only few organisms have been cultivated from this group and their viruses were previously described only through metagenomic reconstructions. Here, we report the first successful cultivation of an Asgard archaeal virus infecting a novel strain of Ca. Lokiarchaeum ossiferum B36. The 16 kbp integrated provirus is capable to excise and replicate independently leading to the formation of virus particles. Network analysis of shared protein clusters with other archaeal viruses places it in a new family, Fylgjaviridae . The host encodes a distinctive repertoire of antiviral defense systems, including Septu, Wadjet, and type II CBASS system, all different from the defense systems of the related strain Ca. L. ossiferum B35. Our cultures provide the first opportunity to study interactions of a virus-host system in Asgards and hold significant potential for developing genetic tools. ### Competing Interest Statement The authors have declared no competing interest. FWF Austrian Science Fund, 10.55776/EFP25, Z437 European Research Council, Advanced Grant #695192: TACKLE Max Planck Society, https://ror.org/01hhn8329 https://www.biorxiv.org/content/10.64898/2026.02.13.705702v1