Reversible inhibition of viral life cycle in response to elevated temperature in a bloom-forming alga

Ocean warming is expected to reshape microbial interactions and community composition, with profound consequences for marine biogeochemical cycles. Host–virus dynamics are central to these processes, yet their response to elevated temperature remains poorly understood. Here, using the bloom-forming alga Gephyrocapsa huxleyi and its specific large dsDNA virus, Emiliania huxleyi virus (EhV), we show that elevated temperature withheld virion production and abolished distinct stages of the viral life cycle. Viral adsorption and early transcription remained active, whereas viral DNA replication and late gene expression were arrested, leading to an intracellular inhibition of infection. Intriguingly, this arrested infection state was reversible following prolonged heatwave conditions. Single-cell analyses revealed that reversibility of infection inhibition occurred both within a small fraction of infected cells and by reinfection by extracellular virions that remained viable during heat exposure in the extracellular milieu. Furthermore, we detected variability in infection inhibition by temperature across several host-virus pairs, suggesting that the effect of temperature is strain-specific. Our findings uncover a temperature-sensitive checkpoint in the viral life cycle, providing a mechanistic framework for understanding how marine heatwaves may reshape virus-driven mortality and carbon cycling in the ocean.