Evolutionary and ecological consequences of chronic infection in Sulfolobus islandicus

Though not often considered from this perspective, virus-host interactions represent a symbiotic interaction that exists along a continuum from antagonistic to mutualistic. In microbial ecology and evolution, this relationship has mostly focused on antagonistic lytic viruses. Lytic viruses are horizontally transferred from one infected host to a new host via the release of viral particles through cell lysis and death. When increases in horizontal transmission increase the fitness of the virus, selection acts to favor traits that would, in turn, increase the virulence of the virus, therefore increasing the antagonism in the virus-host relationship. Recently, there has been a greater appreciation for viruses that follow other life cycles, such as persistent, chronic viruses or temperate viruses. These viruses have a long-term association with their hosts and can be transmitted vertically from mother to daughter cells. Because of this long-term association, viral fitness and host fitness are aligned, and selection acts to favor traits that are more mutualistic. In this thesis, I utilize the model system of the archaeal host Sulfolobus islandicus and its viruses, the Sulfolobus Spindle Shaped Viruses (SSVs), to better understand how chronic infection shapes these microbial populations. I show how chronic infection with SSVs gives the host a competitive benefit against uninfected cells. Using RNAseq and reverse genetics, I show that this competitive benefit is caused by a proteinaceous toxin encoded by the virus, the first of its kind identified in an archaeal system. This competitive phenotype is especially beneficial to the host and virus in the context of diverse natural populations living in the acidic hot spring system and supports the emergent mutualism that exists in this virus-host interaction.U of I OnlyAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD syste