%0 Journal Article %J mSphere %D 2021 %T Bacterial Quorum-Sensing Signal Arrests Phytoplankton Cell Division and Impacts Virus-Induced Mortality %A Pollara, Scott B. %A Becker, Jamie W. %A Nunn, Brook L. %A Boiteau, Rene %A Repeta, Daniel %A Mudge, Miranda C. %A Downing, Grayton %A Chase, Davis %A Harvey, Elizabeth L. %A Whalen, Kristen E. %E McMahon, Katherine %K rcc1731 %X Interactions between phytoplankton and heterotrophic bacteria fundamentally shape marine ecosystems by controlling primary production, structuring marine food webs, mediating carbon export, and influencing global climate. Phytoplankton-bacterium interactions are facilitated by secreted compounds; however, linking these chemical signals, their mechanisms of action, and their resultant ecological consequences remains a fundamental challenge. The bacterial quorumsensing signal 2-heptyl-4-quinolone (HHQ) induces immediate, yet reversible, cellular stasis (no cell division or mortality) in the coccolithophore Emiliania huxleyi; however, the mechanism responsible remains unknown. Using transcriptomic and proteomic approaches in combination with diagnostic biochemical and fluorescent cell-based assays, we show that HHQ exposure leads to prolonged S-phase arrest in phytoplankton coincident with the accumulation of DNA damage and a lack of repair despite the induction of the DNA damage response (DDR). While this effect is reversible, HHQ-exposed phytoplankton were also protected from viral mortality, ascribing a new role of quorum-sensing signals in regulating multitrophic interactions. Furthermore, our data demonstrate that in situ measurements of HHQ coincide with areas of enhanced micro- and nanoplankton biomass. Our results suggest bacterial communication signals as emerging players that may be one of the contributing factors that help structure complex microbial communities throughout the ocean. %B mSphere %V 6 %P e00009–21, /msphere/6/3/mSph.00009–21.atom %G eng %U https://msphere.asm.org/content/6/3/e00009-21 %R 10.1128/mSphere.00009-21