Among all the microbes living in the human gut, viruses also lurk. The University of Pennsylvania School of Medicine's Frederic Bushman and his colleagues characterized that fraction — the virome — in a PNAS paper published online in late February. He and his team examined sequence variability in DNA viruses in the human gut and described the regions of hypervariability they found. Genome Technology's Ciara Curtin recently spoke with Bushman about the virome. What follows is an excerpt of their conversation, edited for space.