Animal metagenomes enriched for circular DNA viruses

Viruses are ubiquitous agents of disease in humans and other animals, and they are drivers of change in all biological systems. With no 'marker gene' shared amongst all viruses which might allow simple querying of biological samples, detection and identification of viral genomes in metagenomic samples has proven difficult. Further, the vast 'sequence space' of the virosphere is currently undersampled, making homology detection by primary sequence alignment of limited use. In this study, powerful viral genome enrichment tools (ultracentrifugation in an iodixanol gradient and rolling circle amplifaction) have been applied to numerous human and animal tissues, focusing on circular DNA viruses. The novel viral genomes assembled from these sequencing reads help expand the viral sequence space, opening the door to better disease association between viruses and their hosts.