Project Summary / Abstract The gut microbiome is linked to human health through diverse mechanisms including immune system priming, colonization resistance, and metabolic functions. Bacteriophages (phages) are a numerically dominant component of this microbial community, but remain challenging to study especially in microbially rich and diverse contexts such as the conventionally-colonized mammalian gut. The overarching research goal of my laboratory is to characterize the causal role of phages in the gut microbiome. In this project, we propose to study two areas in which temperate and virulent phage can influence the gut microbiota. In the first area, we will characterize the relationship between temperate phage l and its cognate bacteria, E. coli, in the conventionally-colonized murine gut. We will then study the significance of specific prophage-encoded functions that are competitively advantageous within the gut microbiome. In the second area, we will develop a methodology to deplete virulent phage from the murine gut and investigate their significance to the gut microbiome, metabolome, and mammalian host during dietary and antibiotic disruption. The completion of this project will produce important insight into the mechanisms by which phage can impact the gut microbiome.