Message in a bubble – communication via extracellular vesicles shapes algal-virus dynamics in the ocean

Communication between microorganisms in the marine environment has immense ecological impact by mediating trophic-level interactions and thus determining community structure. Extracellular vesicles (EVs) are produced by all cell types and can mediate pathogenicity or act as vectors for intracellular communication. However, little is known about the involvement of EVs in microbial interactions in the marine environment. Here we investigated the signaling role of EVs produced during the interaction between the bloom-forming alga Emiliania huxleyi and its specific virus, EhV, which leads to demise of these large-scale oceanic blooms. We found that production of EVs is elevated during viral infection or when cells are exposed to infochemicals derived from infected cells. These vesicles have a unique lipid composition that differs from that of viruses and their infected host cells. Their cargo is composed of specific small RNAs that are predicted to target sphingolipid metabolism and cell-cycle pathways. In both lab and field experiments we demonstrated that treatment with EVs leads to a faster viral infection dynamic. Furthermore, EVs can prolong the half-life of both isolated and natural EhV virions. We propose that extracellular vesicles are exploited by viruses to sustain efficient infectivity and propagation across E. huxleyi blooms. Since these blooms impact the cycling of carbon and other nutrients, this mode of cell-cell communication may influence the fate of the blooms and therefore the composition and flow of nutrients in marine microbial food webs.