Structure and replication cycle of a virus infecting climate-modulating alga <i>Emiliania huxleyi</i>.

Abstract

The globally distributed marine alga <i>Emiliania huxleyi</i> has cooling effect on the Earth's climate. The population density of <i>E. huxleyi</i> is restricted by <i>Nucleocytoviricota</i> viruses, including <i>E. huxleyi</i> virus 201 (EhV-201). Despite the impact of <i>E. huxleyi</i> viruses on the climate, there is limited information about their structure and replication. Here, we show that the dsDNA genome inside the EhV-201 virion is protected by an inner membrane, capsid, and outer membrane. EhV-201 virions infect <i>E. huxleyi</i> by using fivefold vertices to bind to and fuse the virus' inner membrane with the cell plasma membrane. Progeny virions assemble in the cytoplasm at the surface of endoplasmic reticulum-derived membrane segments. Genome packaging initiates synchronously with the capsid assembly and completes through an aperture in the forming capsid. The genome-filled capsids acquire an outer membrane by budding into intracellular vesicles. EhV-201 infection induces a loss of surface protective layers from <i>E. huxleyi</i> cells, which enables the continuous release of virions by exocytosis.