Edited by James L. Van Etten, University of Nebraska, Lincoln, NE, and approved February 1, 2021 (received for review October 15, 2020)Despite years of research in aquatic virology, we remain unable to estimate viral-induced mortality in the ocean and, consequently, to resolve viral impact on nutrient fluxes and microbial dynamics. Here, we assess active infection in algal single cells by subcellular visualization of virus and host transcripts, revealing the coexistence of infected and noninfected subpopulations. We revisit major assumptions of a giant virus’ life cycle: cells can produce...…Edited by James L. Van Etten, University of Nebraska, Lincoln, NE, and approved February 1, 2021 (received for review October 15, 2020)Despite years of research in aquatic virology, we remain unable to estimate viral-induced mortality in the ocean and, consequently, to resolve viral impact on nutrient fluxes and microbial dynamics. Here, we assess active infection in algal single cells by subcellular visualization of virus and host transcripts, revealing the coexistence of infected and noninfected subpopulations. We revisit major assumptions of a giant virus’ life cycle: cells can produce...WW…