The gut virome: the 'missing link' between gut bacteria and host immunity?

The human gut virome includes a diverse collection of viruses that infect our own cells as well as other commensal organisms, directly impacting on our well-being. Despite its predominance, the virome remains one of the least understood components of the gut microbiota, with appropriate analysis toolkits still in development. Based on its interconnectivity with all living cells, it is clear that the virome cannot be studied in isolation. Here we review the current understanding of the human gut virome, specifically in relation to other constituents of the microbiome, its evolution and life-long association with its host, and our current understanding in the context of inflammatory bowel disease and associated therapies. We propose that the gut virome and the gut bacterial microbiome share similar trajectories and interact in both health and disease and that future microbiota studies should in parallel characterize the gut virome to uncover its role in health and disease.