Lipid biomarkers for algal resistance to viral infection in the ocean.

Abstract

Marine viruses play a key role in regulating phytoplankton populations, greatly affecting the biogeochemical cycling of major nutrients in the ocean. Resistance to viral infection has been reported for various phytoplankton species under laboratory conditions. Nevertheless, the occurrence of resistant cells in natural populations is underexplored due to the lack of sensitive tools to detect these rare phenotypes. Consequently, our current understanding of the ecological importance of resistance and its underlying mechanisms is limited. Here, we sought to identify lipid biomarkers for the resistance of the bloom-forming alga <i>Emiliania huxleyi</i> to its specific virus, <i>E. huxleyi</i> virus (EhV). By applying an untargeted lipidomics approach, we identified a group of glycosphingolipid (GSL) biomarkers that characterize resistant <i>E. huxleyi</i> strains and were thus termed resistance-specific GSLs (resGSLs). Further, we detected these lipid biomarkers in <i>E. huxleyi</i> isolates collected from induced <i>E. huxleyi</i> blooms and in samples collected during an open-ocean <i>E. huxleyi</i> bloom, indicating that resistant cells predominantly occur during the demise phase of the bloom. Last, we show that the GSL composition of <i>E. huxleyi</i> cultures that recover following infection and gain resistance to the virus resembles that of resistant strains. These findings highlight the metabolic plasticity and coevolution of the GSL biosynthetic pathway and underscore its central part in this host-virus arms race.