Biological context modulates virus-host dynamics and diversification
Virus-host interactions are fundamental to microbial ecology and evolution, yet they are often studied in simplified systems. To assess the impact of biological complexity, we examined the halophilic bacterium Salinibacter ruber strain M1 and the EM1 virus, a bacteriophage that infects M1, in the presence of additional strains and viruses. In the short term, the presence of a biotic background delayed population-level lysis and reduced EM1 production. In the long term, both M1 and EM1 persisted across all conditions, but their evolutionary trajectories diverged. The virus accumulated many mutations, showed reduced infectivity against its native host, and expanded its host range in the presence of other viruses, highlighting a role of virus-virus interactions in promoting diversification. In contrast, the host accumulated more mutations when evolving with other bacterial strains. Taken together, these findings demonstrate that biological complexity shapes both the ecological dynamics and evolutionary trajectories of virus-host interactions.