For better or for worse, every organism on earth has viruses in its DNA. Just like all organisms these viruses maximize their own success and sometimes this means increasing the success of their hosts. Sulfolobus spindle-shaped virus infects Sulfolobus cells, a single-celled member of the Archaeal Domain. This virus does not kill the cells it infects but instead turns its host cell into a killing machine. This study will identify the conditions in which virus infection leading to killer-archaea makes sense for host, virus, and host-virus pairs. This work will provide a new outlook on host-virus interactions that will better shape understanding of viral infections. Through the ProjectMicrobe curriculum and Illinois Extension network at the University of Illinois this proposal will expand scientific literacy about viruses and their positive and negative impacts on the intimately interconnected human, plant, animal, and microbial worlds.
Virus-host interactions fundamentally shape the course of evolution across the tree of life. These interactions are governed by the evolutionary rules of symbiosis, where viruses are most often considered antagonistic to hosts. The research team will investigate a symbiosis between the model archaeon Sulfolobus islandicus and its chronic virus SSV9. They hypothesize that a killing trait conferred by the virus to infected host cells establishes a conditional mutualism that is dependent on CRISPR-cas immunity, resistance, and the prevalence of infection. They will test this hypothesis using comparative genomics to identify the genetic basis of key symbiosis traits, genetic tools to modify these traits in virus and host strains, quantitative competitive fitness assays for both virus and host, and experimental evolution in the Sulfolobus model system following the evolution and coevolution of host and virus over time. This conditional mutualism provides potent, unexpected outcomes of virus-host interactions that broaden the role of viruses in complex individual-level competitive interactions that are ubiquitous in the natural world.