Viral infection of algal blooms leaves a unique metabolic footprint on the dissolved organic matter in the ocean

Algal blooms are hotspots of primary production in the ocean, forming the basis of the marine food web and fueling the dissolved organic matter (DOM) pool. Marine viruses are key players in controlling algal bloom demise, thereby diverting algal biomass from higher trophic levels to the DOM pool, a process termed the ‘viral shunt’. To decode the metabolic footprint of the ‘viral shunt’ in the marine environment, we induced a bloom of Emiliania huxleyi and followed its succession using an untargeted exometabolomics approach. Here, we show that algal bloom succession induces dynamic changes in the exometabolic landscape. We discovered a set of novel chlorine-iodine-containing metabolites that were induced by viral infection and released during bloom demise. These metabolites were further detected in virus-infected oceanic E. huxleyi blooms. Therefore, we propose that halogenation with both chlorine and iodine is a distinct hallmark of the virus-induced DOM of E. huxleyi, providing insights into the metabolic consequences of the ‘viral shunt’ for marine DOM.