Human microbiome studies have lead to a better understanding of the human body and the role of microbes in defining healthy and diseased individuals. Although great strides have been made toward better understanding the complex microbial interactions inside humans, the majority of studies published focus on bacteria, while most studies have ignored the role of phages in the microbiome.

We identified the human gut phage, crAssphage, a bacteriophage that resides in roughly half of the human population across the globe. Despite crAssphage being highly abundant, its role in humans is still unknown. The phage has only been found computationally and has never been isolated in the lab. Experiments in mouse intestines suggest that the host maybe one of fifteen strains of bacteria, and bioinformatics analysis predicted that the host is probably a Bacteroidetes. We have shown that crAssphage is highly abundant in raw sewage influent. Plaque- and PCR-based assays have been used to identify crAssphage’s host – the first step in dissecting its role in human health and disease.