Dr. Paul Kirchberger Department of Integrative Biology University of Texas at Austin Thursday, April 15, 2021 - 11:10am Online via Zoom Special Information: Please contact Nancy Perkins at firstname.lastname@example.org for Zoom link and passcode Type of Event: Department Seminars Abstract: Single-stranded DNA phages of the family Microviridae have fundamentally different evolutionary origins and dynamics than their more frequently studied double-stranded DNA counterparts. Despite their small size (generally <5kb), which imposes extreme constraints on genomic innovation, microviruses have adapted to become prominent components of viromes in numerous ecosystems and hold a dominant position among viruses in the human gut. Yet until recently, they were known almost exclusively from metagenomic sequence data. By in-vitro synthesizing and transforming their miniature genomes into an E. coli host, I develop an experimentally tractable host-virus system that allows their study in the laboratory. Through building microviruses with combinations of genomic segments from different phages (mimicking diversity observed in natural populations), their interactions with each other and with their hosts can be recreated. Using this approach, I discover the role of a hypervariable genomic region in prophages that defends their hosts against infection by other members of the microvirus population. By detecting microviruses in metagenomic and genomic datasets, I show that this hypervariable region has evolved multiple times independently in response to the preceding evolution of lysogenic ability. These results provide a rare insight into the biology of these elusive phages and emphasize the importance of virus-virus interactions in viral evolution in general. The establishment of a microviral model system also paves the way for gaining a more thorough understanding of the roles of microviruses in the larger ecosystem of the human gut and elsewhere.