To kill or to piggyback: Switching of viral lysis-lysogeny strategies depending on host dynamics.

Viruses wield significant influence over microbial communities and ecosystem function in marine environments. However, the selection of viral life strategies and their impacts on microbial communities remains enigmatic. In this study, we utilized a large-scale macrocosm, established using water samples from a marine coastal region, to enable community-level investigation. Through a prolonged incubation experiment, we aimed to clarify the ramifications of lytic and lysogenic viral activities on microbial community dynamics. We observed a continuous succession in bacterial abundance, growth rate, and community diversity, tightly linked with time series switching between viral lysis and lysogeny. Elevated lytic viral production notably fostered greater bacterial diversity, whereas increased lysogenic viral production corresponded to bacterial communities characterized by heightened abundance and growth rate but reduced diversity. Moreover, discernible shifts in bacterial community compositions, associated with different abundant bacterial taxa, were synchronized with pronounced transitions between viral lysis and lysogeny. Notably, the switch from lysogeny to lysis facilitated the proliferation of initially rare bacterial populations. Our findings suggest that the Kill-the-Winner and Piggyback-the-Winner hypotheses, both elucidating dynamic patterns in virus-host interactions, can synergistically demonstrate the pivotal role of viruses in regulating microbial communities via the lysis-lysogeny switch in marine environments.