Abstract: Phages are master manipulators of bacteria and a potential source of new solutions for engineering gut microbiomes. To investigate the dynamics of phage outbreaks, my lab developed “Phollow”—an in vivo tagging strategy that enables direct visualization of phage replication and spread within living systems. Phollow allows rapid, multiscale screening of conditions that trigger temperate phage lytic replication using live imaging. A unique feature of Phollow is its ability to color-code phages based on their most recent bacterial host, making it possible to track their transmission across microbial communities. When paired with optically transparent zebrafish, Phollow enables single-virion resolution imaging of phage activity in live animals. Our initial studies have uncovered previously hidden spatial and temporal dimensions of phage ecology within the gut. In my seminar, I will present new findings on regulators of phage induction, interbacterial transmission within the gut, and interactions between phage particles and host tissues.